U.S. patent application number 12/075354 was filed with the patent office on 2008-07-03 for black conductive thick film compositions, black electrodes, and methods of forming thereof.
Invention is credited to Michael F. Baker, Keiichiro Hayakawa, Hisashi Matsuno.
Application Number | 20080157033 12/075354 |
Document ID | / |
Family ID | 36675888 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080157033 |
Kind Code |
A1 |
Baker; Michael F. ; et
al. |
July 3, 2008 |
Black conductive thick film compositions, black electrodes, and
methods of forming thereof
Abstract
The present invention provides a method for forming a black
electrode by performing sintering at a temperature in the range of
500-600.degree. C. after applying a lead-free black conductive
composition to a substrate. The aforementioned black electrode
comprises a binder comprising a crystallized glass component. The
aforementioned black conductive composition comprises conductive
particles of black RuO.sub.2, lead-free black ruthenium-based
polyoxide, and mixtures thereof in an amount of 4-30 wt %, based on
the total weight of the composition, a lead-free non-conductive
black oxide in an amount of 0-30 wt %, based on the total weight of
the composition, and a lead-free bismuth-based glass binder in an
amount of 10-50 wt %, based on the total weight of the
composition.
Inventors: |
Baker; Michael F.; (Raleigh,
NC) ; Hayakawa; Keiichiro; (Tokyo, JP) ;
Matsuno; Hisashi; (Tokyo, JP) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1122B, 4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
36675888 |
Appl. No.: |
12/075354 |
Filed: |
March 10, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11369550 |
Mar 7, 2006 |
|
|
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12075354 |
|
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Current U.S.
Class: |
252/519.52 ;
427/77 |
Current CPC
Class: |
C03C 8/22 20130101; C03C
8/16 20130101; H01J 9/02 20130101; C03C 8/14 20130101; H01J
2211/225 20130101; C03C 8/18 20130101; C03C 17/04 20130101 |
Class at
Publication: |
252/519.52 ;
427/77 |
International
Class: |
H01B 1/08 20060101
H01B001/08; B05D 5/12 20060101 B05D005/12 |
Claims
1. A method of forming a lead-free black electrode comprising:
supplying a substrate; supplying a lead-free black conductive
composition comprising, based on the weight percent of the total
composition (a) 4-30 weight percent conductive metal oxides
selected from RuO.sub.2, one or more lead-free ruthenium-based
polyoxides, and mixtures thereof, (b) 10-50 weight percent
lead-free bismuth-based glass binder, wherein said glass binder
comprises Bi.sub.2O.sub.3; ZnO, and B.sub.2O.sub.3 and wherein
Bi.sub.2O.sub.3 is present in an amount of 70-90 weight percent,
based on the total weight of said glass binder; and (c) 0-30 weight
percent lead-free non-conductive black oxide selected from the
group consisting of Cr--Fe--Co type oxide. Cr--Cu--Co type oxide.
Cr--Cu--Mn type oxide, Co.sub.3O.sub.4, and mixtures thereof;
applying said black conductive composition onto said substrate; and
sintering at a temperature in the range of 500-600.degree. C. to
form a black electrode; and wherein said black electrode comprises
a crystallized glass component over the entire sintering range of
500.degree. C.-600.degree. C.
2-7. (canceled)
8. A black electrode formed by the method of claim 1.
9. A black electrode formed from a method comprising supplying a
substrate; supplying a lead-free black conductive composition
comprising, based on the weight percent of the total composition
(a) 4-30 weight percent conductive metal oxides selected from
RuO.sub.2, one or more lead-free ruthenium-based polyoxides, and
mixtures thereof. (b) 10-50 weight percent lead-free bismuth-based
glass binder, wherein said glass binder comprises, based on weight
percent total glass binder: 0-5% BaO, 2-15% B.sub.2O.sub.3, 0-3%
SiO.sub.2, 0-1% Al.sub.2O.sub.3, 8-20% ZnO, and 70-90%
Bi.sub.2O.sub.3; (c) 0-30 weight percent lead-free non-conductive
black oxide; and wherein the surface area to weight ratio of the
conductive metal oxides are in the range of 2-20 m.sup.2/g;
applying said black conductive composition onto said substrate, and
sintering at a temperature in the range of 500-600.degree. C. to
form a black electrode; and wherein said black electrode comprises
a crystallized glass component.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/659,839 filed Mar. 9, 2005.
FIELD OF THE INVENTION
[0002] The present invention is directed to black conductive
compositions, black electrodes made from such compositions and
methods of forming such electrodes, more specifically the present
invention is directed to the use of such compositions, electrodes,
and methods in flat panel display applications, including
alternating-current plasma display panel devices (AC PDP). The
invention is further directed to AC PDP devices themselves.
BACKGROUND OF THE INVENTION
[0003] While the background of the present invention is discussed
in terms of plasma display panel (PDP) applications, it is
understood that the present invention is useful in flat panel
display applications, in general.
[0004] The PDP typically comprises a pair of forward and backward
insulation substrates arranged in opposition to each other to form
a plurality of cells as display elements each defined by the
insulation substrates supported with a constant interval and cell
barriers arranged between the insulation substrates, two crossing
electrodes disposed on internal surfaces of the insulation
substrates with a dielectric layer interposed between the
electrodes which cause electric discharge in a plurality of cells
by application of an alternating current. Due to this application
of alternating current, phosphor screens formed on the wall surface
of the cell barrier emit light and display images which are passed
through the transparent insulation substrate (typically called the
front glass substrate or plate).
[0005] One area of concern for PDP manufacturers is display
contrast, which affects the ultimate picture viewed by the
consumer. To improve the display contrast, it is essential to
decrease the reflection of external light from the electrodes and
conductors arranged on the front glass substrate of the PDP device.
This reflection decrease can be accomplished by making the
electrodes and conductors black as viewed through the front plate
of the display.
[0006] Furthermore, another area of concern for PDP manufacturers
is environmental in nature and is the lead and cadmium contained in
the prior art black conductor compositions and black electrodes of
the PDP device. It is desirable to reduce and/or eliminate the lead
and cadmium contained in the black conductor compositions and
electrodes while still maintaining the required physical and
electrical properties of the compositions and electrodes.
[0007] For example, in Japanese Kokai Patent No. HEI 10[1998]-73233
and its division Japanese Kokai Patent No. 2004-158456,
light-forming black electrode compositions containing conductive
particles consisting of at least one substance chosen from
ruthenium oxide, ruthenium polyoxide, or their mixture and an
inorganic binder, black electrodes using such compositions, plasma
display panels using such black electrodes, and a method for making
such a plasma display panel are disclosed. These literature
references are not directed to lead-free black conductive
compositions. In these references, there are no descriptions on
lead-free black conductive compositions in terms of properties such
as the appearance and strength of black electrodes obtained by
sintering the compositions, electrical properties such as
resistance, and a balance of all the properties for PDP
electrodes.
[0008] Japanese Patent No. 3510761 discloses alkali-developable
photocurable conductive paste compositions for plasma display
panels, easily forming high-precision electrode circuits on large
areas by photolithography and firing below 600.degree. C. Such
compositions contain (A) copolymer resins obtained by the addition
of glycidyl acrylate and/or glycidyl methacrylate to copolymers of
methyl methacrylate and methacrylic acid and/or acrylic acid; (B)
photochemical polymerization initiator; (C) photopolymerizable
monomer; (D) at least one conductive metal powder selected from Au,
Ag, Ni, and Al; (E) glass frit; and (F) a phosphoric acid compound.
Particularly in this literature, a low-melting glass frit is
described using lead oxide as the preferred main component, while
there are no descriptions of lead-free conductive compositions,
especially black conductive compositions.
[0009] Japanese Patent No. 3541125 discloses alkali-developable
curable conductive paste compositions that have excellent adhesion
to the substrate after being fired, with adhesion between layers,
suppression of curling, easy formation of high-precision conductive
circuit patterns in large areas by photolithography, and are
especially useful for forming underlayer electrode circuits of bus
electrodes formed on the front substrate of plasma display panel.
These compositions consist of: (A) carboxy-group-containing resins;
(B) photopolymerizable monomer; (C) photochemical polymerization
initiator; (D) silanol-group-containing synthetic amorphous silica
fine powder; (E) conductive powder; and if needed (F)
heat-resistant black pigment; (G) glass frit; and (H) stabilizer.
In particular, this literature has a description of a low-melting
glass frit using lead oxide as the preferred main component, while
there are no descriptions of lead-free conductive compositions,
especially black conductive compositions.
[0010] Japanese Patent No. 3479463 discloses photocurable
conductive compositions providing excellent adhesion on a substrate
in steps involving drying, exposure, development and firing, and
resolution, satisfying the need for both a sufficient conductivity
and blackness after being fired and discloses plasma display panels
(PDP) with formation of the underlayer (black layer) electrode
circuit using such compositions. The basic first embodiment of the
compositions described in this literature contains (A) black
conductive microparticles having a surface area to weight ratio
larger than 20 m.sup.2/g and containing at least one substance
chosen from ruthenium oxide or other ruthenium compound,
copper-chromium black composite oxide and copper-iron black
composite oxide, (B) an organic binder, (C) a photopolymerizable
monomer, and (D) a photochemical polymerization initiator. The
second embodiment contains (E) inorganic fine particles in addition
to the above components. In this literature, with respect to this
composition, the inorganic fine particles (E) contain, as needed,
glass powder with a softening point of 400-600.degree. C.,
conductive powder, heat-resistant black pigment, silica powder,
etc. However, in the compositions of this literature, glass powder
is not an essential component, and even when a glass component is
added, lead oxide is described as the preferred main component,
with no disclosure of lead-free black conductive compositions.
[0011] Japanese Patent No. 3538387 discloses photocurable
conductive compositions having excellent storage stability,
providing excellent adhesion on substrates in the different steps
of drying, exposure, development and firing, and resolution, and
satisfying the need for both sufficient blackness after being
fired, and discloses plasma display panels (PDP) with the formation
of the underlayer (black layer) electrode circuit using such
compositions. The basic first embodiment of these photocurable
resin compositions contains (A) tricobalt tetroxide
(Co.sub.3O.sub.4) black microparticles, (B) organic binder, (C)
photopolymerizable monomer, and (D) photochemical polymerization
initiator. The second embodiment contains (E) inorganic
microparticles in addition to the above components. In this
literature, with respect to this composition, the inorganic fine
particles (E) contain, as needed, a glass powder with a softening
point of 400-600.degree. C., conductive powder, heat-resistant
black pigment, silica powder, etc. However, the compositions of
this literature do not contain conductive materials such as
ruthenium oxide, and glass powder is not an essential component.
Even when a glass component is added, lead oxide is described as
the preferred main component, with no disclosure of lead-free black
conductive compositions.
[0012] Japanese Patent No. 3538408 discloses photocurable
conductive compositions having excellent storage stability,
providing excellent adhesion on substrates in different steps of
drying, exposure, development and firing, and resolution, and
satisfying the need for both sufficient conductivity and blackness
after being fired, and discloses plasma display panels (PDP) with
the formation of the underlayer (black layer) electrode circuit
using such compositions. The basic first embodiment of these
photocurable resin compositions contains (A) black inorganic
microparticles such as inorganic binder-coated ruthenium oxide or
another ruthenium compound, copper-chromium black composite oxide,
copper-iron black composite oxide, cobalt oxide, etc., (B) organic
binder, (C) photopolymerizable monomer, and (D) photochemical
polymerization initiator. The photocurable compositions described
in this literature are characterized by containing inorganic
binder-coated black inorganic microparticles (A). The inorganic
binder-coated black inorganic microparticles (A) are obtained by
pulverizing molten materials of inorganic microparticles and an
inorganic binder, with an inorganic binder having a softening point
of 400-600.degree. C. and glass powder with lead oxide as the main
component being described as preferred, but with no disclosure of
lead-free black conductive compositions.
[0013] Japanese Kohyo Patent Application No. 2003-521092 (Thompson
plasma) disclosed a method for forming the face plate of a plasma
display panel having a step in which a paste containing a metal
powder and a mineral-based coupling agent is used to deposit an
electrode, as well as a step in which the deposited electrode is
sintered. This invention is characterized by the fact that the
composition of the mineral-based coupling agent and sintering
conditions are adjusted such that the coupling agent is
recrystallized after the deposited electrode is sintered. The
subject of this reference is not the lead-free coupling agent and
is characterized by the fact that the temperature for sintering the
electrode does not exceed 470.degree. C. Also, the purpose of this
reference is to eliminate the yellow color forming during the heat
treatment of the substrate.
[0014] Japanese Kokai Patent Application No. 2002-367518 disclosed
a type of electrode material used for an Ag electrode or black
stripe, which can prevent blisters during sintering by using a
crystallized glass frit that acts as a coupling agent. This
invention is characterized by using a fluorine-containing glass
frit, but the subject of this invention is not a lead-free glass
frit. Therefore, there is also no description regarding the
manufacturing method of a lead-free black electrode or the
lead-free black electrode itself. In particular, the manufacturing
method of a black electrode containing a lead-free crystalline
glass binder is not disclosed in these references.
[0015] Japanese Kokai Patent Application No. 2002-373592 disclosed
a type of electrode material used for an Ag electrode or black
stripe, which can prevent blisters during sintering by using a
crystallized glass frit that acts as a coupling agent. This
invention is characterized by using a lead-containing glass frit,
but the subject of this invention is not the lead-free glass frit.
Although a lead-free glass frit is mentioned in this reference,
there is no description regarding a lead-free black
electroconductive composition using a lead-free bismuth-based
crystallized glass frit or lead-free black electrode using the
aforementioned lead-free black electroconductive composition.
[0016] Japanese Kokai Patent Application No. 2003-223851 (patent
reference 11) disclosed a type of plasma display substrate
structural body and its manufacturing method. For this substrate
structural body of a plasma display with an electrode and
dielectric layer formed on a substrate, the dielectric layer is
formed by a glass layer with a low melting point, the electrode is
formed by a metal layer containing crystallized glass, and the
electrode and dielectric layer are sintered at the same time.
According to this reference, snaking, disconnection, and floating
of the bus electrode or black electrode can be prevented by
reducing the number of rounds of sintering and by using
crystallized glass. However, there is no detailed description
regarding the composition, content, etc. of the crystallized glass,
and the subject is not a lead-free glass composition. In addition,
although it is disclosed that the crystallization peak temperature
of the crystallized glass is lower than 560-590.degree. C., the
specific temperature is not disclosed at all.
[0017] The present inventors therefore desired to provide novel
black conductive compositions to be used in flat panel display
devices, for forming black electrodes having a desirable balance of
all the preferred electrode properties including electrode pattern
properties, blackness, resistance, etc. Furthermore, the present
inventors desired to provide such compositions and electrodes
formed therefrom which are lead-free. Still further, the present
inventors desired to provide flat panel display devices comprising
such electrodes.
BRIEF DESCRIPTION OF THE FIGURES
[0018] FIG. 1 is an expanded perspective diagram illustrating
schematics of the AC PDP device prepared according to one
embodiment of the present invention.
[0019] FIG. 2 is an explanatory diagram of a series of processes of
the method for making the bus electrode and interconnecting
electrodes positioned between said bus electrode and a transparent
electrode on the same glass substrate: (A) a step for applying the
photosensitive thick film composition layer for black electrode
formation; (B) a step for applying a photosensitive thick film
conductive composition for bus electrode formation; (C) a step for
setting an exposed electrode pattern; (D) development step; (E)
firing step.
[0020] FIG. 3 is an explanatory diagram of a series of processes of
the method for making the bus electrode and interconnecting
electrodes positioned between said bus electrode and transparent
electrode on the same glass substrate: (A) a step for applying the
photosensitive thick film composition layer for black electrode
formation; (B) a step for setting an exposed electrode pattern; (C)
development step (D) firing step (E) a step for applying a
photosensitive thick film conductive composition for bus electrode
formation; (F) a step for setting an electrode pattern by imagewise
exposure of the second bus electrode composition layer; (G)
development step; (H) firing step.
[0021] FIG. 4: This diagram shows an electrode pattern for
measuring the ohmic resistance.
EXPLANATION OF SYMBOLS USED IN THE FIGURES
[0022] 1 transparent electrode [0023] 2 address electrode [0024] 3
fluorescent material [0025] 4 cell barrier [0026] 5 front glass
substrate [0027] 6 rear glass substrate [0028] 7 bus conductor
electrode [0029] 7a exposed part [0030] 7b unexposed part [0031] 8
dielectric layer [0032] 9 protective MgO layer [0033] 10 black
electrode (photosensitive thick film electrode layer) [0034] 10a
exposed part [0035] 10b unexposed part [0036] 11 MgO layer [0037]
13 phototool (target)
SUMMARY OF THE INVENTION
[0038] The present invention is directed to methods of forming a
lead-free black electrode comprising: supplying a substrate;
supplying a lead-free black conductive composition comprising,
based on weight percent total composition (a) 4-30 weight percent
conductive metal oxides selected from RuO.sub.2, one or more
lead-free ruthenium-based polyoxides, and mixtures thereof, (b)
10-50 weight percent lead-free bismuth-based glass binder, and (c)
0-30 weight percent lead-free non-conductive black oxide; applying
said black conductive composition onto said substrate; and
sintering at a temperature in the range of 500-600.degree. C. to
form a black electrode; and wherein said black electrode comprises
a crystallized glass component over the entire sintering range of
500-600.degree. C. The present invention is further directed to
electrodes formed by such methods.
DETAILED DESCRIPTION OF THE INVENTION
[0039] The present inventors discovered a method for the
manufacture of a lead-free black electrode having excellent
characteristics using a black conductive composition comprising
conductive metal oxide particles of RuO.sub.2, a lead-free
ruthenium-based polyoxide or its mixture, a lead-free
non-conductive black oxide, and a specific lead-free glass binder
as the main components. That is, the present invention pertains to
a method for forming a black electrode by performing sintering at a
temperature in the range of 500-600.degree. C. after applying a
lead-free black conductive composition to a substrate. In this
method, the aforementioned black electrode contains a binder
comprising a crystallized glass component. The aforementioned black
conductive composition contains conductive metal oxide particles of
RuO.sub.2, a lead-free black ruthenium-based polyoxide, or their
mixture in an amount of 4-30 wt % based on the total weight of the
composition, a lead-free non-conductive black oxide in an amount of
0-30 wt % based on the total weight of the composition, and a
lead-free bismuth-based glass binder in an amount of 10-50 wt %
based on the total weight of the composition.
[0040] The lead-free bismuth-based glass binder of the present
invention comprises at least Bi.sub.2O.sub.3, ZnO, and
B.sub.2O.sub.3 as the main components, with Bi.sub.2O.sub.3 being
present in an amount of 70-90 weight percent, based on the total
weight of the glass component.
[0041] The glass composition of the aforementioned lead-free
bismuth-based glass binder used in the present invention is
preferably in the following range. [0042] BaO: 0-5 wt % [0043]
B.sub.2O.sub.3: 2-15 wt % [0044] SiO.sub.2: 0-3 wt % [0045]
Al.sub.2O.sub.3: 0-1 Wt % [0046] ZnO: 8-20 wt % [0047]
Bi.sub.2O.sub.3: 70-90 wt %.
[0048] The softening point of the aforementioned crystallized
bismuth-based glass binder is preferably in the range of
400-500.degree. C. Also, after firing anywhere in the range
500-600.degree. C., crystal phases must be present in the binder
phase.
[0049] In the present invention, the non conductive black oxide is
preferably a Cr--Fe--Co oxide, Cr--Cu--Co oxide, Cr--Cu--Mn oxide,
CO.sub.3O.sub.4, or their mixture. In the present invention, the
conductive black oxide is a ruthenium-based polyoxide, preferably
Bi.sub.2Ru.sub.2O.sub.7, CuxBi.sub.2-xRuO.sub.7,
GdBiRu.sub.2O.sub.7.
[0050] The present invention also includes the black electrode
manufactured using the black conductive composition.
[0051] The method of the present invention can provide a black
electrode with low contact resistance (ohmic resistance), good
blackness (low L* value), and good balance other electrode
characteristics.
[0052] The black electrode of the present invention comprises a
crystallized glass component. The crystallized component is one
whose crystalline structure can be identified by means of X-ray
diffraction. In the present invention, a bismuth-based glass forms
the crystallized glass component. The bismuth-based glass can be
partially crystallized. There is no need to fully crystallize said
bismuth-based glass.
[0053] The present invention involves the use of at least one
substrate, and the black electrodes are formed on the substrate. If
necessary, transparent electrodes made of ITO, etc., can also be
formed between the substrate and the black electrodes. Conductive
metal electrodes can also be formed on the black electrodes. The
substrate is a transparent glass substrate, such as the front glass
substrate of a PDP.
[0054] The composition used for the black electrodes is described
below.
(A) Conductive Metal Oxide Particles
[0055] The black conductive compositions of the present invention
comprise (a) conductive metal oxides (oxides with metallic
conductivity) (RuO.sub.2 and or ruthenium polyoxide as the
conductive component). The ruthenium polyoxide is a type of
pyrochlore, which is a multicomponent compound of Ru.sup.+4,
Ir.sup.+4, or their mixture (M'') represented by the general
formula shown below:
(M.sub.xBi.sub.2-x)(M'yM''.sub.2-y)O.sub.7-z
In the formula, M is selected from a group consisting of yttrium,
thallium, indium, cadmium, lead, copper, and rare earth materials;
M' is selected from a group consisting of platinum, titanium,
chromium, rhodium, and antimony; M'' is ruthenium, iridium, or
their mixture; x is 0-2, or x.ltoreq.1 with respect to monovalent
copper; y is 0-0.5 but when M' is rhodium or is more than 1 of
platinum, titanium, chromium, rhodium, or antimony, y is 0-1, and z
is 0-1 but when M is bivalent lead or cadmium, this is at least
equal to about x/2.
[0056] The above ruthenium-based pyrochlore oxide is described in
detail in U.S. Pat. No. 3,583,931, which is herein incorporated by
reference.
[0057] Lead containing ruthenium-based pyrochlore oxides may be
used in the present invention when a lead-containing system is
acceptable. Examples of such oxides include, lead ruthenate
Pb.sub.2Ru.sub.2O.sub.6, Pb.sub.1.5Bi.sub.0.5Ru.sub.2O.sub.6.5,
PbBiRu.sub.2O.sub.6.75. However, these lead containing oxides are
typically not desirable due to the effort to decrease lead content
in electrode compositions.
[0058] Preferred ruthenium polyoxides are lead-free and include
bismuth ruthenate Bi.sub.2Ru.sub.2O.sub.7,
Cu.sub.xBi.sub.2-xRuO.sub.7, GdBiRu.sub.2O.sub.7, and mixtures
thereof. These materials are readily available in purified form and
have no adverse effect on the glass binder. These materials are
also stable up to 1000.degree. C. in air and relatively stable even
under a reductive atmosphere.
[0059] Since the thick film composition of the present invention
utilizes a Bi-based glass frit, BiRu pyrochlore, as the conductive
oxide component, is particularly useful due to the chemical
compatibility of the oxide and frit and decreased expense of the
oxide component. For example, although RuO.sub.2 functions as a
black conductive oxide component, the Ru content in RuO.sub.2 is
about 70%, thus it is very expensive. BiRu pyrochlore has a Ru
content of about 30%, which is one half of RuO.sub.2, undergoes no
significant chemical reaction with Ag below 600.degree. C., and has
good wetting with glass compared with black pigments other than
RuO.sub.2 and Ru, therefore it is a preferred lead-free black
conductive oxide component.
[0060] The content of ruthenium oxide and/or ruthenium pyrochlore
oxide based on the overall composition weight is 3-50 wt %,
preferably 6-30 wt %, more preferably 8-25 wt %, and most
preferably 9-20 wt %.
[0061] The surface area to weight ratio of the conductive metal
oxide(s) of the present invention is in the range of 2 to 20
m.sup.2/g. In one embodiment, the range is 5 to 15 m.sup.2/g. In a
further embodiment, the range of surface area to weight ratio is 6
to 10 m.sup.2/g.
[0062] The black conductive compositions of the present invention
can be used for the black electrode layer in the two layer
structure of a bus electrode. Typically, a bus electrode comprises
a highly conductive metal layer and a black electrode as its under
layer (between the bus electrode and transparent substrate). The
compositions of the present invention are suitable for such
applications. The black electrode layer of the present invention
comprises the conductive metal oxides, as described in (A) above as
a necessary component. In addition to the conductive metal oxides
of (A) above, the black electrode layer may also, optionally
comprise the conductive metal particles described in (B) below.
When the black electrode layer comprises the conductive metal
particles of (B), a single layer structure can be used (i.e., the
highly conductive metal layer and black electrode layer are
combined in one layer).
(B) Conductive Metal Particles of the Black Conductive
Compositions
[0063] As noted above, the black composition of the present
invention may optionally, comprise precious metals including gold,
silver, platinum, palladium, copper and combinations thereof.
Virtually any shape metal powder, including spherical particles and
flakes (rods, cones, and plates) may be used in the compositions of
the present invention. The preferred metal powders are selected
from the group comprising gold, silver, palladium, platinum, copper
and combinations thereof. It is preferred that the particles be
spherical. It has been found that the dispersion of the invention
should not contain a significant amount of conductive metal solids
having a particle size of less than 0.2 .mu.m. When particles of
this small size are present, it is difficult to adequately obtain
complete burnout of the organic medium when the films or layers
thereof are fired to remove the organic medium and to effect
sintering of the inorganic binder and the metal solids. When the
dispersions are used to make thick film pastes, which are usually
applied by screen printing, the maximum particle size should not
exceed the thickness of the screen. It is preferred that at least
80 percent by weight of the conductive solids fall within the
0.5-10 .mu.m range.
[0064] In addition, it is preferred that the surface area to weight
ratio of the optional electrically conductive metal particles not
exceed 20 m.sup.2/g, preferably not exceed 10 m.sup.2/g and more
preferably not exceed 5 m.sup.2/g. When metal particles having a
surface area to weight ratio greater than 20 m.sup.2/g are used,
the sintering characteristics of the accompanying inorganic binder
are adversely affected. It is difficult to obtain adequate burnout
and blisters may appear.
[0065] Often although not required, copper oxide is added to
improve adhesion. The copper oxide should be present in the form of
finely divided particles, preferably ranging in size from about 0.1
to 5 microns. When present as Cu.sub.2O, the copper oxide comprises
from about 0.1 to about 3 percent by weight of the total
composition, and preferably from about 0.1 to 1.0 percent. Part or
all of the Cu.sub.2O may be replaced by molar equivalents of
CuO.
(C) Non-Conductive Oxide
[0066] It is also possible to add a non-conductive substance into
the black conductive composition used in the present invention.
Commercially available inorganic black pigments can be used as the
preferred non-conductive oxides. Examples include non-conductive
black oxides, such as Cr--Fe--Co oxide, Cr--Cu--Co oxide,
Cr--Cu--Mn oxide, Co.sub.3O.sub.4, or their mixture. In the present
invention, the shape of the non-conductive substance is not
important. When the dispersion is used to prepare a thick film
paste that is usually applied by means of screen printing, the
maximum particle size should not exceed the thickness of the
screen. It is preferred that at least 80 wt % of the non-conductive
solid have a particle size in the range of 0.1-1.0 .mu.m. The
content of the non-conductive solid in the total composition is in
the range of 0-30 wt %, preferably in the range of 0-15 wt %, based
on the total weight of the composition.
(D) Glass Binder
[0067] The glass binder (also known as "frit") used in the present
invention enhances sintering of the conductive and non conductive
particles. The glass binder used in the present invention is a
crystallized glass binder containing no lead.
[0068] The glass binder is a lead-free and cadmium-free Bi based
amorphous glass. Other lead-free, low-melting glasses are P based
or Zn--B based compositions. However, P based glass does not have
good water resistance, and Zn--B glass is difficult to obtain in
the amorphous state, hence Bi based glasses are preferred. Bi glass
can be made to have a relatively low melting point without adding
an alkali metal and has little problems in making a powder. In the
present invention, Bi-based glass, especially lead-free
crystallizable glass having the following specific composition, is
the most preferred.
(I) Glass Composition
[0069] BaO: 0-5 wt %
[0070] B.sub.2O.sub.3: 2-15 wt %
[0071] SiO.sub.2: 0-3 wt %
[0072] Al.sub.2O.sub.3: 0-1 wt %
[0073] ZnO: 8-20 wt %
[0074] Bi.sub.2O.sub.3: 70-90 wt %
(II) Softening Point
[0075] 400-500.degree. C.
[0076] In the specification of this patent application, the
softening point is measured by means of differential thermal
analysis (DTA).
(III) Crystallized Glass Component.
[0077] Crystallized glass phases must be present in the binder
after firing at temperatures in the range of 500-600.degree. C.
[0078] In the specification of this patent application, the
crystallized glass phases can be easily observed by X-ray
diffraction. When the Bi-based glass of the present invention is
sintered at a temperature in the range of 500-600.degree. C.,
crystals can be observed by means of X-ray diffraction.
[0079] In the present invention, the composition, softening point,
and crystallization behavior of the glass binder are all important
characteristics for ensuring that a good balance of properties of
the black electrode is achieved.
[0080] When the softening point is below 400.degree. C., melting of
the glass may occur while organic materials are decomposed,
allowing blisters to occur in the composition. Therefore it is
preferred that the softening point of the glass is >400.degree.
C. On the other hand, the glass must soften sufficiently at the
firing temperature employed, so the softening point should be
<500.degree. C., if the softening point exceeds 500.degree. C.
electrode peeling occurs at the corners and properties such as
resistance, etc., are affected, compromising the balance of the
electrode properties.
[0081] The glass binders used in the present invention preferably
have a D.sub.50 (i.e., the point at which 1/2 of the particles are
smaller than and 1/2 are larger than the specified size) of 0.1-10
.mu.m as measured by a Microtrac. More preferably, the glass
binders have a D.sub.50 of 0.5 to 1 .mu.m. Usually, in an
industrially desirable process, a glass binder is prepared by the
mixing and melting of raw materials such as oxides, hydroxides,
carbonates, etc., making into a cullet by quenching, mechanical
pulverization (wet, dry), then drying in the case of wet
pulverization. Thereafter, if needed, classification is carried out
to the desired size. It is desirable for the glass binder used in
the present invention to have an average particle diameter smaller
than the thickness of the black conductive layer to be formed
[0082] The content of the glass binder is preferably in the range
of 10-50 wt %, more preferably, in the range of 25-45 wt %, based
on the total weight of the composition. When the proportion of the
glass binder is reduced, the adhesion to the substrate is
weakened.
[0083] The composition of the present invention may contain organic
compounds. The organic compounds used in the present invention
include an organic polymeric binder, photopolymerization initiator,
photocurable monomer, organic medium, etc. They will be explained
below.
(E) Organic Polymeric Binder
[0084] The polymeric binder is important for use in the composition
of the present invention. The water-based development possibility
should be taken into consideration when selecting the polymeric
binder. A polymeric binder with high resolution must be selected.
The following binders satisfy these requirements. In other words,
these binders are comonomers or inter-polymers (mixed polymers)
prepared from (1) a non-acidic comonomer containing a
C.sub.1-C.sub.10 alkyl acrylate, C.sub.1-C.sub.10 alkyl
methacrylate, styrene, substituted styrene, or their combination
and (2) an acidic comonomer in an amount of at least 15 wt % of the
total weight of the polymer and having a component containing an
ethylenically unsaturated carboxylic acid.
[0085] The presence of the acidic comonomer component in the
composition is important to the technology of the present
invention. Depending on its acidic functional groups, development
becomes possible in an aqueous solution base, such as an aqueous
solution containing 0.4 wt % of sodium carbonate. If the content of
the acidic comonomer is less than 15%, the composition cannot be
completely scoured by the aqueous base. If the content of the
acidic comonomer is more than 30%, the stability of the composition
becomes poor under the development conditions, and only partial
development occurs in the image forming part. Examples of proper
acidic comonomers include acrylic acid, methacrylic acid, crotonic
acid, or other ethylenically unsaturated monocarboxylic acids,
fumaric acid, itaconic acid, citraconic acid, vinyl succinic acid,
maleic acid, or other ethylenically unsaturated dicarboxylic acids,
their hemiesters, and, in some cases, their anhydrides and their
mixtures. Methacryl polymers are more preferred than acryl polymers
since they can combust more cleanly in a low-oxygen atmosphere.
[0086] When the aforementioned non-acidic comonomer is the
aforementioned alkyl acrylate or acryl methacrylate, the content of
such a non-acidic comonomer is at least 50 wt %, preferably 70-75
wt %, of the polymeric binder. If the non-acidic comonomer is
styrene or substituted styrene, it is preferred that the content of
such an non-acidic comonomer be 50 wt % of [that of] the polymeric
binder, while the other 50 wt % is an acidic anhydride, such as the
hemiester of maleic anhydride. The preferred substituted styrene is
.alpha.-methylstyrene.
[0087] Although it is not preferred, the non-acidic part of the
polymeric binder may contain about 50 wt % or less of another
non-acidic comonomer to substitute the alkyl acryalte, alkyl
methacrylate, styrene, or substituted styrene of the polymer.
Examples include acrylonitrile, vinyl acetate, and acrylamide.
However, since complete combustion becomes more difficult in this
case, it is preferred to use such a monomer at less than about 25
wt % of the total amount of the polymeric binder. The binder can be
a single copolymer or a mixture of copolymers as long as the
aforementioned various conditions can be satisfied. It is also
possible to add a small amount of other polymeric binders in
addition to the aforementioned copolymer. Examples include
polyethylene, polypropylene, polybutylene, polyisobutylene,
ethylene-propylene copolymer, and other polyolefins as well as
polyethylene oxide and other lower alkylene oxide polymers.
[0088] These polymers can be manufactured by means of the solution
polymerization technology that is commonly used in the field of
acrylic ester polymerization.
[0089] Typically, the aforementioned acidic acrylic ester polymer
can be manufactured as follows. An .alpha.- or .beta.-ethylenically
unsaturated acid (acidic comonomer) is mixed with one or several
types of copolymerizable vinyl monomers (non-acidic comonomer) in
an organic solvent with a relatively low boiling point
(75-150.degree. C.) to obtain a 10-60% monomer mixture solution. A
polymerization catalyst is then added into the obtained monomer
mixture to perform polymerization. Next the obtained mixture is
heated to the reflux temperature of the solvent under normal
pressure. After the polymerization reaction is virtually finished,
the generated acidic polymer solution is cooled to room
temperature. A sample is recovered, and the viscosity, molecular
weight, and acid equivalent of the polymer are measured.
[0090] The aforementioned acid-containing polymeric binder is
preferably has molecular weight of less than 50,000.
[0091] When the aforementioned composition is coated by means of
screen printing, it is preferred that the Tg (glass transition
temperature) of the polymeric binder exceed 60.degree. C.
[0092] The content of the organic polymeric binder is usually in
the range of 5-45 wt % of the total amount of the dried
photopolymerizable layer.
(F) Photopolymerization Initiator
[0093] A desirable photopolymerization initiator is thermally
inactive but can generate free chemical groups when exposed to
chemical rays at a temperature of 185.degree. C. or lower. Such a
photopolymerization initiator includes a substituted or
non-substituted polynuclear quinone, which is a compound having two
intramolecular rings in a conjugated carbon ring. Examples include
9,10-anthraquinone, 2-methyl anthraquinone, 2-ethyl anthraquinone,
2-t-butyl anthraquinone, octamethyl anthraquinone,
1,4-naphthoquinone, 9,10-phenanthrenequinone,
benzo[a]anthracene-7,12-dione, 2,3-naphthacene-5,12-dione,
2-methyl-1,4-naphthoquinone, 1,4-dimethyl anthraquinone,
2,3-dimethyl anthraquinone, 2-phenyl anthraquinone, 2,3-diphenyl
anthraquinone, retene quinone,
7,8,9,10-tetrahydronaphthacene-5,12-dione, and
1,2,3,4-tetrahydrobenzo[a]anthracene-7,12-dione. Other useful
photopolymerization initiators are disclosed in U.S. Pat. No.
2,760,863 (however, several of them are thermally active even at a
low temperature of 85.degree. C.; they are vicinal ketaldonyl
alcohols, such as benzoin or pivaloin; methyl and ethyl ethers of
benzoin or other acyloin ethers; .alpha.-methyl benzoin,
.alpha.-allyl benzoin, .alpha.-phenyl benzoin, thioxanthone and its
derivatives, and hydrocarbon-substituted aromatic acyloins
containing hydrogen donors).
[0094] Photoreductive dyes and reducing agents can be used as the
initiator. Examples include those disclosed in U.S. Pat. No.
2,850,445, U.S. Pat. No. 2,875,047, U.S. Pat. No. 3,097,96 [sic],
U.S. Pat. No. 3,074,974, U.S. Pat. No. 3,097,097, and U.S. Pat. No.
3,145,104, phenazine, oxazine, and quinones, such as Michler's
ketone, ethyl Michler's ketone, benzophenone, etc., 2,4,5-triphenyl
imidazoyl dimer formed with a hydrogen donor containing a leuco
dye, and their mixtures (disclosed in U.S. Pat. No. 3,427,161, U.S.
Pat. No. 3,479,185, and U.S. Pat. No. 3,549,367). Also, the
sensitizer disclosed in U.S. Pat. No. 4,162,162 can be used
together with photopolymerization initiator and photopolymerization
inhibitor. The content of the photopolymerization initiator or
photopolymerization initiator system is in the range of 0.05-10 wt
% based on the total amount of the dried photopolymerizable
layer.
(G) Photocurable Monomer
[0095] The photocurable monomer component used in the present
invention contains at least one type of addition polymerizable
ethylenically unsaturated compound having at least one
polymerizable ethylene group.
[0096] Such a compound can cause the formation of the polymer,
depending on the presence of free groups, and a chain-extending
addition polymerization can take place. The monomer compound has a
non-gas form, that is, it has a boiling point higher than
100.degree. C. and can provide plasticity to the organic polymeric
binder.
[0097] Preferable monomers that can be used either alone or in
combination with other monomers include t-butyl (meth)acrylate,
1,5-pentanediol di(meth)acrylate, (N,N-dimethyl aminoethyl
(meth)acrylate, ethylene glycol di(meth)acrylate, 1,4-butanediol
di(meth)acrylate, diethylene glycol di(meth)acrylate, hexamethylene
glycol di(meth)acrylate, 1,3-propanediol di(meth)acrylate,
decamethylene glycol di(meth)acrylate, 1,4-cyclohexanediol
di(meth)acrylate, 2,2-dimethylolpropane di(meth)acrylate, glycerol
di(meth)acrylate, tripropylene glycerol di(meth)acrylate, glycerol
tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, compounds
disclosed in U.S. Pat. Nos. 3,380,381,
2,2-di(p-hydroxyphenyl)-propane di(meth)acrylate, pentaerythritol
tetra(meth)acrylate, triethylene glycol diacrylate,
polyoxyethyl-1,2-di-(p-hydroxyethyl) propane dimethacrylate,
bisphenol A di-[3-(meth)acryloxy-2-hydroxypropyl)ether, bisphenol A
di-[2-(meth)acryloxyethyle) ether, 1,4-butanediol
di-(3-methacryloxy-2-hydroxypropyl)ether, triethylene glycol
dimethacrylate, polyoxypropyl trimethyrol propane triacrylate,
butylene glycol di(meth)acrylate, 1,2,4-butanediol
tri(meth)acrylate, 2,2,4-trimethyl-1,3-pentanediol
di(meth)acrylate, 1-phenylethylene-1,2-dimethacrylate, diallyl
fumarate, styrene, 1,4-benzenediol dimethacrylate,
1,4-diisopropenyl benzene, and 1,3,5-triisopropenyl benzene (in
this case, "(meth)acrylate" includes both "acrylate and
methacrylate)".
[0098] Ethyleneiacally unsaturated compounds with a molecular
weight of at least 300 can also be used. Examples include
C.sub.2-C.sub.15 alkylene glycol or polyalkylene glycols having
1-10 ether bonds, or the compounds disclosed in U.S. Pat. No.
2,927,022, such as the alkylene or polyalkylene glycol acrylate
manufactured from compounds having addition polymerizable ethylene
bonds, especially when they are present as terminal groups.
[0099] Other useful monomers are disclosed in U.S. Pat. No.
5,032,490. Preferable monomers include polyoxyethylated
trimethylolpropane tri(meth)acrylate, ethylated pentaerythritol
acrylate, trimethylolpropanetri(meth)acrylate, dipentaerythritol
monohydroxy pentacrylate, and 1,10-decanediol dimethacrylate.
[0100] Other preferable monomers include
monohydroxypolycaprolactone monoacrylate, polyethylene glycol
diacrylate (molecular weight: about 200), and polyethylene glycol
dimethacrylate (molecular weight: about 400). The content of the
unsaturated monomer component is in the range of 1-20 wt % based on
the total weight of the dried photopolymerizable layer.
(H) Organic Medium
[0101] The main purpose of using an organic medium is so that the
dispersion of the finely pulverized solid content of the
aforementioned composition can be easily coated on ceramics or
other substrates. Consequently, first of all, the organic medium
must be able to disperse the solid content while maintaining the
proper stability. Secondly, the rheology characteristics of the
organic medium must provide the dispersion with a good coating
characteristic.
[0102] For the organic medium, the solvent component, which may
also be a solvent mixture, should be properly selected so that the
polymer and other organic components can be completely dissolved in
it. The selected solvent should be inactive (no reaction) with
other components in the paste composition. The selected solvent
should have very high volatility so that it can evaporate from the
dispersion even if coated at a relatively low temperature under
atmospheric pressure. The solvent should have such a volatility
that the paste can dry quickly on a screen at ordinary room
temperature during the printing operation. The preferable solvent
used for the paste composition has a normal-pressure boiling point
lower than 300.degree. C., preferably, lower than 250.degree. C.
Examples of such a solvent include aliphatic alcohols, acetic
esters, propionic esters, or the esters of the aforementioned
alcohols; pine resin, .alpha.- or .beta.-terpineol, or their
mixture, or other terpinenes; ethylene glycol, ethylene glycol
monobutyl ether, butyl Cellosolve acetate, or other esters of
ethylene glycols; butyl Carbitol, butyl Carbitol acetate, Carbitol
acetate, or other carbitol esters; Texanol
(2,2,4-trimethyl-1,3-pentanediol monoisobutyrate), and other
appropriate solvents.
[0103] In addition to the aforementioned components, the following
substances can also be added into the composition of the present
invention.
(I) Additional Components
[0104] Dispersants, stabilizers, plasticizers, mold releasing
agents, dispersants [sic], stripping agents, defoaming agents,
lubricants, and other additional components that are well known in
this field can also be added into the composition. General examples
of the proper substances are disclosed in U.S. Pat. No.
5,32,490.
Applications and Uses
[0105] If the aforementioned photosensitive material is added into
the black electroconductive composition, a photosensitive
composition can be prepared. The black electroconductive
photosensitive composition can be formed as a film using spinning,
dipping, or other film coating technology, or using screen
printing, chemical etching, or other conventional patterning
technology.
[0106] When the black electroconductive composition of the present
invention is used as an electroconductive material, that
composition can be formed on a dielectric layer or a glass
substrate (for example, a bare glass panel).
[0107] The black conductive compositions of the present invention
may also be utilized in processes for patterning thick film
electrically functional patterns using a photosensitive polymer
layer. For example, as described in Patent Publication WO 02/03766
A2 to Keusseyan herein incorporated by reference. Keusseyan
describes a process for forming a pattern having electrically
functional properties on a substrate comprising the steps of: (a)
providing a photosensitive layer having a tacky surface disposed on
a substrate; (b) providing a transfer sheet comprising a removable
support and at least one layer of a thick film composition disposed
on the support; (c) image-wise exposing the photosensitive tacky
surface to form an imaged layer having unexposed tacky and exposed
non-tacky areas; (d) applying the thick film composition of the
transfer sheet onto the imaged layer; (e) separating the transfer
sheet from the substrate wherein the thick film substantially
remains on the support in the exposed non-tacky areas to form a
patterned thick film composition; and (f) subjecting the patterned
thick film composition to heat thereby forming a patterned
article.
[0108] When the black conductive compositions of the present
invention are used as conductive materials, these compositions may
be formed on various substrates, including a dielectric layer or
glass substrate (e.g., bare glass panel).
[0109] The composition of the present invention may be patterned on
a transparent substrate, topped with a photosensitive material, and
exposed to UV, etc., from the transparent substrate (back side) to
form a photomask.
[0110] Flat Panel Display Applications
[0111] The present invention includes black electrodes formed from
the above black conductive compositions. The black electrodes of
the present invention can be favorably used in flat panel display
applications, particularly in alternating-current plasma display
panel devices. The black electrodes can be formed between the
device substrate and conductor electrode array.
[0112] In one embodiment, the electrode of the present invention is
used in AC PDP applications, as described below. It is understood
that the compositions and electrodes of the present invention may
be used in other flat panel display applications and their
description in AC PDP devices is not intended to be limiting. An
example of the black electrodes of the present invention used in an
alternating-current plasma display panel is explained below. This
description includes two-layer electrodes comprising a black
electrode between the substrate and conductor electrode (bus
electrode). Also, the method for making an alternating-current
plasma display panel device is outlined.
[0113] The alternating-current plasma display panel device consists
of front and back dielectric substrates with a gap and an electrode
array containing parallel first and second electrode composite
groups in a discharge space filled with ionizing gas. The first and
second electrode composite groups face each other perpendicularly
with the discharge space in the middle. A certain electrode pattern
is formed on the surface of the dielectric substrate, and a
dielectric material is coated on the electrode array on at least
one side of the dielectric substrate. In this device, at least the
electrode composite on the front dielectric substrate is fitted
with the conductor electrode array group connected to the bus
conductor on the same substrate, and with the black electrode of
the present invention formed between the above substrate and the
above conductor electrode array.
[0114] FIG. 1 illustrates the black electrode of the present
invention in an AC PDP. FIG. 1 shows the AC PDP using the black
electrode of the present invention. As shown in FIG. 1, the AC PDP
device has the following components: underlying transparent
electrode (1) formed on glass substrate (5); black electrode (10)
formed on the transparent electrode (1) (the black conductive
composition of the present invention is used for the black
electrode (10)); bus electrode (7) formed on the black electrode
(10) (bus electrode (7) is a photosensitive conductor composition
containing conductive metal particles from metals selected from Au,
Ag, Pd, Pt and Cu or combinations thereof (this is explained in
more detail below)). The black electrode (10) and bus conductor
electrode (7) are exposed imagewise by actinic radiation to form a
pattern, developed in a basic aqueous solution, and fired at an
elevated temperature to remove the organic components and to sinter
the inorganic material. The black electrode (10) and bus conductor
electrode (7) are patterned using an identical or very similar
image. The final result is a fired, highly conductive electrode
composite, which appears to be black on the surface of the
transparent electrode (1), and when placed on the front glass
substrate, reflection of external light is suppressed.
[0115] The word `black` used in this specification means a black
color with significant visual contrast against a white background.
Therefore, the term is not necessarily limited to black which
possesses the absence of color. The degree of "blackness" may be
measured with a colorimeter to determine an L-value. The L-value
represents lightness where 100 is pure white and 0 is pure black.
Although shown in FIG. 1, the transparent electrode described below
is not necessary in forming the plasma display device of the
present invention.
[0116] When a transparent electrode is used, SnO.sub.2 or ITO is
used for forming the transparent electrode (1), by chemical vapor
deposition or electro-deposition such as ion sputtering or ion
plating. The components of the transparent electrode and method for
its formation in the present invention are those of the
conventional AC PDP production technology, well known to those in
the art.
[0117] As shown in FIG. 1, the AC PDP device of the present
invention is based on a glass substrate having dielectric coating
layer (8) and MgO coating layer (11) over the patterned and fired
metallization.
[0118] The conductor lines are uniform in line width and are not
pitted or broken, have high conductivity, optical clarity and good
transparency between lines.
[0119] Next, a method for making both a bus electrode and black
electrode over the optional transparent electrode on the glass
substrate of the front plate of a PDP device is illustrated.
[0120] As shown in FIG. 2, the formation method of the one
embodiment of the present invention involves a series of processes
((A)-(E)).
[0121] (A) A process of applying a black electrode-forming
photosensitive thick film composition layer (10) on a transparent
electrode (1) formed using SnO.sub.2 or ITO according to a
conventional method known to those in the art, on the glass
substrate (5), then drying the thick film composition layer (10) in
a nitrogen or air atmosphere. The black electrode composition is a
lead-free black conductive composition of the present invention.
(FIG. 2(A)).
[0122] (B) Applying to the first applied black electrode
composition layer (10) a photosensitive thick film conductor
composition (7) for forming the bus electrodes, then drying the
thick film composition layer (7) in a nitrogen or air atmosphere.
The photosensitive thick film conductive composition is described
below. (FIG. 2(B)).
[0123] (C) Imagewise exposing the first applied black electrode
composition layer (10) and the second bus electrode composition
layer (7) to actinic radiation (typically a UV source) through a
phototool or target (13) having a shape corresponding to a pattern
of the black and bus electrodes arranged in correlation with the
transparent electrodes (1), using exposure conditions that yield
the correct electrode pattern after development. (FIG. 2(C))
[0124] (D) A process of developing the exposed parts (10a, 7a) of
the first black conductive composition layer (10) and the second
bus electrode composition layer (7) in a basic aqueous solution,
such as a 0.4 wt % sodium carbonate aqueous solution or other
alkali aqueous solution. This process removes the unexposed parts
(10b, 7b) of the layers (10, 7). The exposed parts (10a, 7a) remain
(FIG. 2 (D)). The developed product is then dried.
[0125] (E) After process, (D), the parts are then fired at a
temperature of 450-650.degree. C., depending upon the substrate
material, to sinter the inorganic binder and conductive components
(FIG. 2 (E)).
[0126] Black stripes can be used in the present invention. The
black stripes can be formed at the same time as the bus electrodes,
or formed separately from the bus electrodes. When the black
stripes are formed at the same time as the bus electrodes, said
black stripes are formed at the same time as the black
electrodes.
[0127] The formation method of the second embodiment of the present
invention is explained below with FIG. 3. For convenience, the
numbers assigned for each part of FIG. 3 are same as FIG. 2. The
method of the second embodiment involves a series of processes
(A'-H').
[0128] A'. A process of applying a black electrode-forming
photosensitive thick film composition layer (10) on a transparent
electrode (1) formed using SnO.sub.2 or ITO according to a
conventional method known to those in the art, on the glass
substrate (5), then drying the thick film composition layer (10) in
a nitrogen or air atmosphere. The black electrode composition is a
lead-free black conductive composition of the present invention.
(FIG. 3(A)).
[0129] B'. Imagewise exposing the first applied black electrode
composition layer (10) to actinic radiation (typically a UV source)
through a phototool or target (13) having a shape corresponding to
a pattern of the black electrodes arranged in correlation with the
transparent electrodes (1), using exposure conditions that yield
the correct black electrode pattern after development. (FIG.
3(B)).
[0130] C'. A process of developing the exposed part (10a) of the
first black conductive composition layer (10) in a basic aqueous
solution such as a 0.4 wt % sodium carbonate aqueous solution or
other alkali aqueous solution for removal of the unexposed parts
(10b) of the layers (10) (FIG. 3 (C)). The developed product is
then dried.
[0131] D'. After process, (C'), the parts are then fired at a
temperature of 450-650.degree. C., depending upon the substrate
material, to sinter the inorganic binder and conductive components
(FIG. 3(D)).
[0132] E'. A process of applying the bus electrode-forming
photosensitive thick film composition layer (7) to the black
electrode (10a) according to the fired and patterned part (10a) of
the first photosensitive thick film composition layer (10), then
drying in a nitrogen or air atmosphere (FIG. 3(E)). The
photosensitive thick film conductor composition is described
below.
[0133] F'. Imagewise exposing the second applied bus electrode
composition layer (7) to actinic radiation (typically a UV source)
through a phototool or target (13) having a shape corresponding to
a pattern of the bus electrodes arranged in correlation with the
transparent electrodes (1) and black electrode (10a), using
exposure conditions that yield the correct electrode pattern after
development. (FIG. 3(F)).
[0134] G'. A process of developing the exposed part (7a) of the
second bus conductive composition layer (7) in a basic aqueous
solution such as a 0.4 wt % sodium carbonate aqueous solution or
other alkali aqueous solution for removal of the unexposed parts
(7b) of the layers (7) (FIG. 3 (G)). The developed product is then
dried.
[0135] H'. After process, (G'), the parts are then fired at a
temperature of 450-650.degree. C., depending upon the substrate
material, to sinter the inorganic binder and conductive components
(FIG. 3 (H)).
[0136] The third embodiment (not shown) involves a series of
processes ((i)-(v)) shown below.
[0137] (i) The process of loading a black electrode composition on
a substrate. This black electrode composition is the black
conductive composition of the present invention described
above.
[0138] (ii) The process of loading a photosensitive conductive
composition on a substrate. This photosensitive conductive
composition is described below.
[0139] (iii) The process of setting an electrode pattern by
imagewise exposure of the black composition and conductive
composition by actinic radiation.
[0140] (iv) The process of developing the exposed black composition
and conductive composition by a basic aqueous solution for removal
of the area not exposed to actinic radiation.
[0141] (v) The process of firing the developed conductive
composition.
[0142] Next, an example of using the black electrode of the present
invention in an AC plasma display panel will be explained. The
following explanation is based on an example of a two-layer
electrode, with black electrodes formed between the substrate and
conductive metal electrodes (bus electrodes). Referring back to
FIG. 1, after forming the transparent electrode (1) in relation to
the black electrode (10) and bus electrode (7) on the front glass
substrate (5), the front glass substrate assembly is covered with
dielectric layer (8), then coated with MgO layer (11). Next, the
front glass substrate (5) is combined with rear glass substrate
(6). Cell barriers 4 are formed on rear glass substrate 6, with
fluorescent substance 3 being screen coated on the inside to
exhibit display cells. The electrode formed on the front substrate
assembly is perpendicular to the address electrode formed on the
rear glass substrate. The discharge space formed between the front
glass substrate (5) and rear glass substrate (6) is sealed with a
glass seal and at the same time a discharge gas mixture is sealed
into the space. The AC PDP device is thus assembled.
[0143] Next, bus conductive compositions for bus electrodes are
explained below.
[0144] The bus conductive compositions used in the present
invention may be photosensitive thick film conductive compositions
available commercially. As noted above, the bus conductive
composition comprises (a) conductive metal particles of at least
one metal selected from Au, Ag, Pd, Pt, and Cu and combinations
thereof; (b) at least one inorganic binder; (c) photoinitiator; and
(d) photocurable monomer. In one embodiment of the present
invention, the bus conductive composition comprises Ag.
[0145] The conductive phase is the main component of the above
composition, typically comprising silver particles with a particle
diameter within the range of 0.05-20 .mu.m (microns) in a random or
thin flake shape. The bus conductive composition is herein
described with reference to one embodiment comprising silver
particles, but is not intended to be limiting. When a
UV-polymerizable medium is used together with the composition, the
silver particles should have a particle diameter within the range
of 0.3-10.mu.. Preferred compositions should contain 65-75 wt % of
silver particles based on the overall thick film paste.
[0146] The silver conductive composition for forming a bus
electrode may also contain 0-10 wt % of a glass binder and/or 0-10
wt % of refractory materials that do not form glass or a precursor
as needed, in addition to Ag. Examples of the glass binder include
lead-free glass binders described in the Claims of the present
invention. Refractory materials that do not form glass and
precursors are, e.g., alumina, copper oxide, gadolinium oxide,
tantalum oxide, niobium oxide, titanium oxide, zirconium oxide,
cobalt iron chromium oxide, aluminum, copper, various commercially
available inorganic pigments, etc.
[0147] Objectives for adding the second, third, and more inorganic
additives in addition to such main components are for control of
the pattern shape, suppression or promotion of sintering during
firing, adhesive property retention, control of the main-metal
component diffusion, inhibition of discoloration near the bus
electrode, control of resistance, control of the thermal expansion
coefficient, mechanical strength retention, etc. The type and
amount are selected as needed within the range of having no
significant adverse effects on the basic performance.
[0148] Furthermore, the silver conductive compositions may also
contain 10-30 wt % of a photosensitive medium in which the above
particulate materials are dispersed. Such a photosensitive medium
may be polymethyl methacrylate and a polyfunctional monomer
solution. This monomer is selected from those with a low volatility
for minimizing evaporation during the silver conductive composition
paste preparation and printing/drying process before the UV curing.
The photosensitive medium also contains a solvent and UV initiator.
The preferred UV polymerizable medium includes a polymer based on
methyl methacrylate/ethyl acrylate in a 95/5 ratio (weight based).
The silver conductive composition described above has a viscosity
of 10-200 Pa-s, for a free-flowing paste.
[0149] Suitable solvents for such a medium are, but not limited to,
butyl Carbitol acetate, Texanol.RTM. and .beta.-terpineol.
Additional solvents that may be useful include those listed in
Section (G) Organic Medium, above. Such a medium may be treated
with dispersants, stabilizers, etc.
[0150] Preparation of Photosensitive Wet-Developable Pastes
(A) Preparation of Organic Materials
[0151] The solvent and acrylic polymer were mixed, stirred, and
heated to 100.degree. C. to complete dissolution of the binder
polymer. The resulting solution was cooled to 80.degree. C.,
treated with the remaining organic components, stirred to complete
the dissolution of all solids, passed through a 325-mesh filter
screen, and cooled.
(B) Preparation of Paste
[0152] The paste was prepared by mixing an organic carrier, one or
more monomers, and other organic components in a mixing vessel
under yellow light. The inorganic materials were then added to the
mixture of organic components. The entire composition was then
mixed until the inorganic particles were wetted with the organic
material. This mixture was roll-milled using a 3-roll mill. The
resulting paste was used as obtained or was passed through a
635-mesh filter screen. At this point, the paste viscosity was
adjusted by carriers or solvents to a viscosity most suitable for
optimum processing.
[0153] Care was taken to avoid dirt contamination in the process of
preparing paste compositions and in preparing parts, since such
contamination can lead to defects
(I) Preparation of 2-Layer Test Parts
(1) Formation of Black Electrodes
[0154] A glass substrate (glass substrate for PP8 display produced
by NEG) with a transparent electrode thin film ITO formed one side,
was cut to a size of 2.times.3 inch. The paste was screen printed
on its surface using a screen mask with a pattern of about 5.5-cm
square. The black conductive paste of the present invention was
applied onto the glass substrate, with the aforementioned
transparent electrode thin film ITO formed on it, by screen
printing, using a 380-mesh polyester screen. The product was dried
at 100.degree. C. in a warm-air circulating oven for 15 min. The
dry film thickness was in the range of 4-6 .mu.m.
(2) Formation of Conductive Metal Electrodes (Bus Electrodes)
[0155] Next, the photo-imageable Ag conductor paste was applied by
screen printing using a 380-mesh polyester screen. The
photo-imageable Ag conductor paste was a photosensitive Ag paste
containing 2 wt % of bismuth-based glass frit B and 65-75 wt % of
Ag powder (average particle size: 1.3-2.0 .mu.m).
[0156] The product was dried again at 100.degree. C. in a warm-air
circulating oven for 15 min. The dry film thickness was in the
range of 6-8 .mu.m. Consequently, the dry film thickness of the
two-layer structure was in the range of 10-14 .mu.m.
(3) UV Pattern Exposure
[0157] The part with the two-layer structure was then exposed,
through a phototool, to a collimated UV light source (small UV
exposure machine: I rays (365 nm)) (illuminance: 5-20 mW/cm.sup.2;
exposure energy: 200 mJ/cm.sup.2).
(4) Development
[0158] The exposed part was placed on a conveyor then led into a
spray developer containing a 0.4 wt % sodium carbonate aqueous
solution as the developer solution. The developer solution
temperature was maintained at 30.degree. C., and sprayed at 10-20
psi. The part was subjected to a development time of 1.5 times TTC
(Time to Clean). The developed part was dried by blowing off the
excess water in a forced air stream
(5) Firing
[0159] The dried product was fired in an air atmosphere using a
belt furnace (produced by Koyo Thermosystem Co., Ltd.) using a
trapezoidal firing profile having a total length of 1.5 h with a
peak temperature of 580.degree. C. (7 min) or in a 20-min box
profile.sup..dagger-dbl. at a prescribed temperature.
(II) Preparation Single Layer Test Parts.
(1) Printing and Drying Single Layer.
[0160] A glass substrate (glass substrate for PP8 display produced
by NEG) was cut into a size of 2.times.3 inch. The paste was screen
printed on its surface using a screen mask with a pattern of about
5.5-cm square. Screen printing was carried out using a 380-mesh
polyester screen. The part was dried at 100.degree. C. in a
warm-air circulating oven for 15 min. The dry film thickness was in
the range of 4-6 .mu.m.
(2) Firing
[0161] The dried product was fired in an air atmosphere using a
belt furnace (produced by Koyo Thermosystem Co., Ltd.) using a
trapezoidal firing profile having a total length of 1.5 h with a
peak temperature of 580.degree. C. (7 min) or in a 20-min box
profile.sup..dagger-dbl. at a prescribed temperature.
EXAMPLES
[0162] The amount of the constituent components will be expressed
in weight percent (wt %) for the following application examples and
controls unless specified otherwise.
Test Procedures
[0163] The following items were evaluated for the application
examples and controls.
Dried Black Thickness
[0164] The dry film thickness of the black electrode was measured
at four different points using a contact profilometer.
Dried Ag/Black Thickness
[0165] The Ag electrode was coated on the dried film of the black
electrode, then dried. The dry film thickness of the Ag/Black
composite layer was measured using the same method as black
electrode above.
L Value Ag/Black Two Layer
[0166] After firing, the blackness viewed from the back of the
glass substrate is measured mechanically. For blackness, the color
(L*) was measured using the optical sensor SZ and color measurement
system .SIGMA. 80 of Nippon Denshoku Kogyo with calibration using a
standard white plate, with 0 being pure black and 100 pure
white.
Contact Resistance
[0167] The contact resistance was measured as follows. The
electrode structure consisted of a first layer made of a
transparent electrode film (ITO), a second layer made of the black
conductive composition (black electrode), and a conductive metal
electrode (containing Ag as the main component) as the third layer,
as shown in FIG. 4. This electrode can be manufactured by following
the steps (1)-(5) of said (I). The resistance between electrodes A
and B in the pattern shown in FIG. 4 was measured. The resistance
was measured using the 4-terminal method and R6871E produced by the
ADVANTEST Corporation.
[0168] Since the specific resistance of the black electrode in the
second layer is higher than that of the transparent electrode in
the first layer and the conductive metal electrode in the third
layer, the resistance of the black electrode in the second layer is
essentially measured using this method. This resistance measurement
is an indication of how good the electrical connection is between
the transparent electrode layer and the conductive metal electrode
layer (via the black electrode layer). The resistance so measured
is called the "contact resistance".
X-Ray Diffraction Analysis
XRD Single Layer Test Part. (Black Only)
[0169] A glass substrate (glass substrate for PP8 display produced
by NEG) was cut a size of 2.times.3 inch. The black conductive
paste was screen printed on its surface using a screen mask with a
pattern of about 5.5-cm square. Screen printing was carried out
using a 380-mesh polyester screen. The part was dried at
100.degree. C. in a warm-air circulating oven for 15 min. The dry
film thickness was in the range of 4-6 .mu.m. The dried part was
first belt fired at 400.degree. C. to remove organic material, then
fired in a box furnace at 450.degree. C., 500.degree. C.,
550.degree. C. or 600.degree. C.
XRD 2 Layer Test Part. (Black+Ag)
[0170] A glass substrate (glass substrate for PP8 display produced
by NEG) was cut a size of 2.times.3 inch. The Ag conductive paste
was screen printed on its surface using a screen mask with a
pattern of about 5.5-cm square. Screen printing was carried out
using a 380-mesh polyester screen. The part was dried at
100.degree. C. in a warm-air circulating oven for 15 min.
[0171] The black conductive paste was then screen printed over the
dry Ag layer using a screen mask with a pattern of about 5.5-cm
square. Screen printing was carried out using a 380-mesh polyester
screen. The part was dried at 100.degree. C. in a warm-air
circulating oven for 15 min.
[0172] The dried 2-layer part was first belt fired at 400.degree.
C. to remove organic material, then fired in a box furnace at
450.degree. C., 500.degree. C., 550.degree. C. or 600.degree.
C.
[0173] After firing, the test parts were subjected to X-ray
diffraction analysis (Using Rigaku Corporation --RINT1500) to
identify the presence of crystal phases in the fired electrode
layer.
[0174] After eliminating those X-ray diffraction peaks assignable
to the conductive and non-conductive materials, the level of
crystallization in the binder phase was assessed as being either,
none, (i.e, no glass binder crystallization observed) low (i.e. a
low level of glass binder crystallization), medium (i.e. a moderate
level of glass binder crystallization) and high (i.e. a high level
of glass binder crystallization. Note, even at a high level of
binder crystallization, amorphous glass phase still remains.
[0175] Next, the application examples and comparative examples will
be explained. The manufacturing conditions of the electrodes are as
described in (I) (1)-(5) and (II), (1)-(2).
[0176] The components listed in the following Tables 1-6 were used
in the following application examples. Also, BiRu pyrochlore powder
(Ru mixture A; specific surface area: 11 m.sup.2/g) was used as the
ruthenium polyoxide, and a Cr--Fe--Co oxide was used as the black
powder A.
TABLE-US-00001 TABLE 1 Organic Binder Composition in Weight Percent
Total Organic Binder Composition wt % wt % Organic Binder Organic
Binder A Organic Binder B Solvent A Texanol [Transliteration] 46.50
55.10 Acrylic Resin A Acrylic resin (Carboset XPD1234) 34.80 36.20
Initiator A Photopolymerization initiator (Irgacure 651: ) 2.60
Initiator B Photopolymerization initiator (DETX: diethyloxysantone)
8.80 2.30 Initiator C Photopolymerization initiator (EDAB: Ethyl 4-
8.30 2.20 dimethylaminobenzoate) Inhibitor A Stabilizer (TAOBN)
0.06 0.07 Resin B PVP/VA copolymer of vinyl pyrrolidone and vinyl
acetate 1.50 1.50 Total 100.0 100.0
TABLE-US-00002 TABLE 2 Vehicle for Black paste Vehicle for Black
paste wt % Organic Binder A 18.00 Organic Binder B 18.00 Monomer A
TMPEOTA (trimethylolpropane ethoxy 7.90 triacrylate) Solvent A
Solvent Texanol 5.50 Organic Additive A Additive Malonic acid 1.00
Organic Additive B Additive BHT 0.20 Total 50.60
TABLE-US-00003 TABLE 3 Vehicle for Ag Paste Vehicle for Ag paste wt
% Organic Binder B 19.00 Monomer A TMPEOTA (trimethylolpropane
ethoxy 4.10 triacrylate) Organic Additive A Additive Malonic acid
0.20 Organic Additive B Additive BHT 0.20 Solvent A Solvent Texanol
3.00 Total 26.50
TABLE-US-00004 TABLE 4 Ag paste recipe Ag paste recipe w % paste
name Ag-1 Ag-2 Ag-3 Ag-4 Ag-5 Ag powder A 71.0 69.0 69.0 69.0 69.0
Bi Frit B 2.5 3.0 3.0 Bi Frit A 3.0 3.0 Black powder A 1.0 1.0
Vehicle for Ag 26.5 28.0 28.0 27.0 27.0 Paste Total 100.0 100.0
100.0 100.0 100.0
TABLE-US-00005 TABLE 5 Black paste recipe w % Paste name Black-
Black-1 Black-2 Black-3 Black-4 Black-5 Black-6 Black-7 Black-8
Black-9 Black-10 11 Black-12 Vehicle for Black 50.6 51.0 51.0 52.9
55.6 52.6 57.1 55.3 55.6 50.2 50.2 50.2 Pb Frit A 29.7 Pb Frit B
27.8 30.1 Pb Frit C Pb Frit D 29.7 Bi Frit A 35.8 Bi Frit B 33.1 Bi
Frit C 35.5 36.0 27.0 18.0 Bi Frit D 35.5 9.0 18.0 Bi Frit E 33.6
Ru Mixture A 6.9 6.9 6.9 7.1 7.5 7.1 7.7 7.4 7.5 7.8 7.8 7.8 Black
powder A 6.6 6.6 6.6 6.8 7.2 6.8 7.4 7.1 7.2 6.0 6.0 6.0 Total
100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
100.0 Paste name Black- Black- Black- Black- Black- Paste name 13
14 15 16 17 Black-18 Black-19 Black-20 Black-21 Black-22 Black-23
Vehicle for 50.2 50.2 51.3 51.2 51.0 50.8 50.5 50.8 50.7 50.6 50.3
Black Pb Frit A Pb Frit B Pb Frit C Pb Frit D Bi Frit A Bi Frit B
16.4 16.1 15.8 15.3 14.8 8.1 8.0 7.8 Bi Frit C 9.0 26.7 Bi Frit D
27.0 36.0 18.2 17.9 17.6 17.0 16.4 27.0 26.6 26.2 8.2 Bi Frit E Ru
Mixture A 7.8 7.8 7.4 8.1 8.8 10.2 11.6 7.3 8.0 8.7 9.8 Black
powder A 6.0 6.0 6.8 6.8 6.8 6.7 6.7 6.7 6.7 6.7 5.1 Total 100.0
100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
TABLE-US-00006 TABLE 6 Glass Compositions in Weight Percent Total
Glass Composition Glass Name Bi Frit A Bi Frit D Bi Frit C Bi Frit
B Bi Frit E Pb Frit B Pb Frit C Pb Frit A Pb Frit D PbO 67.5 62.06
70 69 Bi.sub.2O.sub.3 69.82 71.8 76 56.8 58.8 SiO2 7.11 1.0 0.5
18.2 16.2 27.5 30.81 15 18 Al.sub.2O.sub.3 2.13 0.5 0.5 2.3 2.3
2.57 B.sub.2O.sub.3 8.38 9.6 7.5 9.1 9.1 3 1.84 15 13 CaO 0.53 ZnO
12.03 14.4 15 12.7 12.7 2.72 BaO 2.9 0.5 0.9 0.9 MgO 2 Total 100
100 100 100 100 100 100 100 100 Average particle size (um) [.mu.m]
0.9 0.6 0.7 0.9 0.9 0.8 0.9 1 1 Softening point (DTA) 500 449 425
568 556 553 597 464 491 DTA crystallization peak reference value
597
Application Example 1 and Comparative Examples 1-4
[0177] Ru mixture A, and Black powder A were mixed with different
glass powders to manufacture the paste compositions listed in Table
7. The aforementioned operations (I) and (II) were carried out to
manufacture test samples for each application example and
control.
TABLE-US-00007 TABLE 7 Black Composition in Weight Percent Total
Composition Control Control Exam- Control Control 1 2 ple 1 3 4 Ag
Paste Ag-1 Paste name Black 1 Black 2 Black 3 Black 4 Black 5 (wt
%) (wt %) (wt %) (wt %) (wt %) Vehicle for Black paste 50.6 51.03
51.0 52.9 55.6 Pb Frit A 29.7 Bi Frit A 35.8 Ru Mixture A 6.9 6.9
6.9 7.1 7.5 Bi Frit B 33.1 Bi Frit C 35.5 Bi Frit D 35.5 Black
powder A 6.6 6.6 6.6 6.8 7.2 Total 100.0 100.0 100.0 100.0
100.0
Results
[0178] The results are shown in Table 8.
TABLE-US-00008 TABLE 8 Control 1 Control 2 Example 1 Control 3
Control 4 Conductive BiRu BiRu BiRu BiRu BiRu Dried Black
thickness/um [.mu.m] 5.1 4.9 4.9 4.9 4.9 Dried Ag/black
thickness/um 11.7 11.0 10.5 11.9 11.0 Calculated dried Ag
thickness/um 6.6 6.1 5.6 7.0 6.1 TTC in sec 6.6 6.9 6.7 6.5 7.3 L
color for Ag/Black on ITO 10.6 6.9 6.5 10.6 9.5 Ohmic resistance
(ohm) one time fired 13.8 7.7 8.1 10.2 5.6 Ohmic resistance (ohm)
two times fired 64.7 85.4 18.7 27.1 17.0 Ohmic resistance (ohm)
three times fired 336.6 259.7 30.4 101.6 87.9 XRD - Level of
crystal. XRD 2-layer fired @ 400.degree. C. None None None None
None XRD 2-layer fired @ 450.degree. C. None Medium Medium None
None XRD 2-layer fired @ 500.degree. C. None Medium Medium None
None XRD 2-layer fired @ 550.degree. C. Medium Medium Medium Medium
None XRD 2-layer fired @ 600.degree. C. High None Medium High None
XRD black only fired @ 400.degree. C. None None None None None XRD
black only fired @ 450.degree. C. None None Medium None None XRD
black only fired @ 500.degree. C. None Medium Medium None None XRD
black only fired @ 550.degree. C. Medium Low Medium None None XRD
black only fired @ 600.degree. C. High None Med-Low Low None
[0179] As can be seen from the aforementioned application examples
and controls, the lead-free black conductive composition of the
present invention can retain the desired characteristics, with a
good balance black electrode properties. In particular, in
Application Example 1, the contact resistance (ohmic resistance in
table 8) after repeated firing is the lowest, and the L value the
lowest.
Results of X-Ray Diffraction
[0180] Only Example 1 shows acceptable electrode performance, in
particular low ohmic resistance.
[0181] Example 1 has crystals present in the binder phase after
firing at 500.degree. C., 550.degree. C. and 600.degree. C., i.e.
crystals are present over the entire range from 500.degree. C. to
600.degree. C.
[0182] Example 1 clearly falls within the scope of the present
invention.
[0183] All the controls have unacceptable ohmic resistance. While
some controls have crystals present in the binder phase after
firing at some specific temperatures, they do not have crystals in
the binder phase at all temperatures between 500.degree. C. and
600.degree. C., and as such do not fall within the scope of this
invention.
Application Examples 24 and Controls 5-12
[0184] In order to evaluate the reproducibility of the contact
resistance performance of black paste 3 (based on Bi frit C). Black
paste 3 was tested in a 2-layer structure with 3 more Ag pastes,
(Ag-2, Ag-3 and Ag-4. Examples 2, 3, and 4 respectively). In
examples 2-4 the length of the profile was increased to 2.5 hrs
(verses 1.5 hrs for example 1).
[0185] Black pastes 1,2,4 and 5 (used in controls 1-4 above) and
black paste 6 (based on Bi frit E) was also included for
comparison. (Controls 5-12)
Results
[0186] The results are shown in Table 9.
TABLE-US-00009 TABLE 9 Set No. Control 5 Control 6 Example 2
Control 7 Control 8 Ag paste: Ag-2 Ag Description: Ag 69 wt % Bi
Frit A: 3 wt % Black paste Black-1 Black-2 Black-3 Black-6 Black-4
Black Description Bi Frit A Bi Frit D Bi Frit C Bi Frit E Bi Frit B
Ohmic R fire 25 14 19 35 28 @580 C. .times. 2.5 h x1 fire 100 37 26
264 170 x2 fire 684 74 24 184 274 x3 Set No. Control 9 Example 3
Control 10 Control 11 Control 12 Example 4 Ag paste Ag-3 Ag-4 Ag
Description Ag: 69 wt % Ag: 69 wt % Bi Frit B: 3 wt % Bi Frit A: 3
wt % Black powderA: 1 wt % Black paste Black-1 Black-3 Black-6
Black-4 Black-1 Black-3 Black Description Bi Frit A Bi Frit C Bi
Frit E Bi Frit B Bi Frit A Bi Frit C Ohmic R @580 C. .times. 2.5 h
fire x1 47 17 46 31 23 18 fire x2 151 30 370 355 126 23 fire x3 585
49 180 491 517 22
[0187] Irrespective of the Ag conductor used for the 2 layer
testing, the ohmic resistance performance of black paste 3 (based
on Bi frit C) is good, even with a longer firing profile.
[0188] The black pastes based on the other Bi frits consistently
show poor ohmic resistance performance.
Application Examples 5-11 and Controls 13-15
[0189] The purpose of examples 5-11 and controls 13-15 was to
investigate if Bi-frit C (which performs well in examples 1-4
above) can be blended with Bi-frit D (which did not perform well in
controls above) to give black paste compositions with acceptable
ohmic resistance performance.
Examples 5-11, and controls 13-15 were fired using a 1.5 hr long
profile.
Results
[0190] The results are shown in Table 10.
TABLE-US-00010 TABLE 10 Example Example Set No. Example 5 Example 6
Example 7 Example 8 Control 13 Example 9 10 11 Control 14 Control
15 Ag Ag-3 Ag-5 Ag Description Ag: 69 wt % Ag: 69 wt % Bi Frit B: 3
wt % Bi Frit B: 3 wt % Black powder A: 1 wt % Black Black-10
Black-11 Black-12 Black-13 Black-14 Black-10 Black-11 Black-12
Black-13 Black-14 Black Description Bi Frit C Bi Frit C Bi Frit C
Bi Frit C Bi Frit C Bi Frit C Bi Frit C Bi Frit C Bi Frit C Bi Frit
C 100 75 50 25 0 100 75 50 25 0 Bi Frit D Bi Frit D Bi Frit D Bi
Frit D Bi Frit D Bi Frit D Bi Frit D Bi Frit D Bi Frit D Bi Frit D
0 25 50 75 100 0 25 50 75 100 resistivity/mohm/sq@5 um 6.7 6.9 6.7
7.4 7.1 7.0 7.0 7.3 7.1 7.5 Ohmic R fire x1 7 7 7 7 7 7 7 7 6 6
fire x2 11 15 20 32 43 13 12 24 55 76 fire x3 14 20 28 32 51 16 16
30 143 173 dried Black thickness/um 4.3 4.3 4.0 4.0 4.1 4.3 4.3 4.0
4.0 4.1 dried Ag/Black thickness/um 9.8 10.0 9.8 9.6 10.0 10.0 10.0
9.7 9.6 9.5 fired thickness/um 3.8 4.0 3.5 4.0 3.9 3.7 3.6 3.6 3.9
3.5 edge curl/um 2.1 1.6 1.5 1.7 1.9 2.0 1.9 2.0 1.5 1.8 L-color
for Ag/Black on ITO 7.9 7.7 8.2 8.0 7.8 6.5 6.4 6.9 7.0 6.4
[0191] The results in table 10 show that black pastes consisting of
a blend of Bi frit D and Bi frit C can give acceptable ohmic
resistance performance, particularly when the level of Bi frit C is
high.
[0192] The purpose of controls 17-24 was to investigate if Bi-frit
B could be blended with Bi-frit D to give black paste compositions
with acceptable ohmic resistance performance (i.e. can 2 frits
which do not give good performance in a black paste when used on
their own, perform well when blended?)
Controls 17-24 were fired using a 1.5 hr long profile.
Results
[0193] The results are shown in Table 11.
TABLE-US-00011 TABLE 11 Set No. Control 17 Control 18 Control 19
Control 20 Control 21 Control 22 Control 23 Control 24 Ag Ag-4 Ag
Ag: 69 wt %. Bi Frit A: 3 wt %. Black powder A: 1 wt % Description
Black Black-15 Black-16 Black-17 Black-18 Black-19 Black-20
Black-21 Black-22 Black Description Bi Frit B Bi Frit B Bi Frit B
Bi Frit B Bi Frit B Bi Frit B Bi Frit B Bi Frit B Bi Frit D Bi Frit
D Bi Frit D Bi Frit D Bi Frit D Bi Frit D Bi Frit D Bi Frit D
mixture 1 mixture 1 mixture 2 mixture 3 mixture 4 mixture 5 mixture
6 mixture 7 resistivity/mohm/sq@5 um 7.6 7.2 7.2 7.6 7.5 6.6 7.6
7.4 Ohmic R fire x1 11 9 8 7 7 9 8 7 fire x2 234 NA 156 116 99 160
168 154 fire x3 762 NA 490 591 477 388 366 403 dried Black
thickness/um 4.0 4.0 4.0 3.9 4.0 4.0 4.0 4.0 dried Ag/Black
thickness/ 10.0 9.9 9.8 9.8 9.9 9.8 9.8 9.8 um fired thickness/um
4.1 4.0 4.4 4.4 4.6 4.2 4.1 4.1 edge curl/um 1.7 2.4 1.9 2.9 2.9
2.7 2.5 2.6 L-color for Ag/Black on 10.8 10.2 10.1 10.0 9.4 10.1
10.0 9.6 ITO
The blending of Bi-frit B and Bi-frit D consistently gives poor
performance
[0194] In Application Examples 12-14, the effect of varying the
film thickness of the black electrode was evaluated. For these
examples, the dried film thickness was varied from 3-5 .mu.m. The
results obtained are shown in table 12.
TABLE-US-00012 TABLE 12 Example Example Set No. Example 12 13 14 Ag
Ag-1 Black Black-23 Black Description Bi Frit C + B mixture Dried
Black thickness Thin-film Standard Thick-film dried Black
thickness/um 3.0 4.0 5.0 dried Ag/Black thickness/um 8.1 9.0 10.5
resistivity/mohm/sq@5 um 9.0 9.1 8.7 ohmic R fire x1 4.3 5.2 3.5
fire x2 11.2 10.5 10.5 fire x3 18.0 15.8 15.5 fired thickness/um
3.7 3.8 4.1 edge curl/um 1.0 1.5 1.2 L-color for Ag/Black on ITO
12.5 5.1 4.0
[0195] The contact resistance performance is maintained regardless
of the thickness of the black layer.
* * * * *