Note: Descriptions are shown in the official language in which they were submitted.
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PRECURSOR PASTE AND METHOD OF PRODUCING THE SAME
FIELD OF THE INVENTION
The present invention relates to a photosensitive paste and, more
particularly, to a
precursor paste that can be advantageously used when forming a fine structure.-
The
present invention also relates to a method of producing the fine structure by
using the
paste, and to the fine structure thus produced. A typical example of the fine
structure is
ribs formed on a back panel for a plasma display panel.
BACKGROUND OF THE INVENTION
The flat panel displays that are small in thickness and light in weight have
been
gaining much attention as the next generation display apparatus. As an example
of thin
flat panel display of large screen, the plasma display panel (PDP) has been
used for
business use, and recently for home use as wall-hung television receiver.
The PDP has such a constitution as schematically shown in Fig. 1. While only
one
discharge cell 56 is shown in PDP 50 for the purpose of simplicity, the
discharge cell 56 is
delimited by a front glass substrate 61, a back glass substrate 51 and ribs
(also referred to
as barner rib, separator or barrier wall) 54 of fine structure. The front
glass substrate 61
has transparent display electrodes 63~consisting of scan electrodes and
sustaining
electrodes, a transparent dielectric layer 62 and a transparent protective
layer 64 formed
thereon. The back glass substrate 51 has address electrodes 53 and a
dielectric layer 52
formed thereon. The display electrode 63 consisting of the scan electrode and
the
sustaining electrode, and the address electrodes 53 are perpendicular to each
other and
arranged at equal intervals. Each of the discharge cells 56 has a fluorescent
layer 55
formed on the inner wall thereof and is filled with rare gas (for example, Ne-
Xe gas) so
that spontaneous light emission occurs through plasma discharge between the
electrodes.
In the PDP 50 described above, the rib 54 is made generally in fine structure
of
ceramic to which the fine structure of the present invention can be applied.
Fig. 2 shows
the ribs 54 of the present invention schematically as will be described in
detail below, the
ribs 54 being provided on the back glass substrate 51 together with the
address electrodes
53 so as to form the back panel of the PDP.
Since shape and dimensional accuracy of the ribs have significant influence on
the
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performance of the PDP, many methods have been proposed to create the ribs.
One such
method involves molding a precursor ceramic paste into a desired shape and
then sintering
the paste to create the densified ceramic ribs. Various improvements have been
made on
the mold and method employed for producing the same. For example, such a
method of
forming the ribs is proposed that a metal or glass is used as the mold
material, a curable
coating solution is placed between the surface of the glass substrate and the
mold to form
the ribs, then the mold is removed after the coating solution has been cured,
and the
substrate onto which the cured coating solution has been transferred is fired
(See JP 9-
12336). The coating solution is a paste consisting of glass powder of low
melting point as
a major component. This method of forming the ribs, however, has various
problems such
that the mold must be produced with high machining accuracy, the i~bs tend to
include
bubbles, the ribs can easily peel off the glass substrate, and it is necessary
to keep the mold
and the glass substrate in close contact with each other under reduced
pressure, which
requires installation of a pressure reducing apparatus that adds to the
producing cost and
requires skilled operator.
In addition to the improvements on the mold and method employed for producing,
various improvements have been made on the rib forming paste. For example, in
order to
enable it to form a pattern of high aspect ratio and high accuracy, there has
been proposed
a photosensitive paste comprising a phosphorus-containing compound, a
photosensitive
organic component and fine inorganic particles as essential components with
emphasis on
the restriction of gelation (JP 9-218509).
SUMMARY OF THE INVENTION
The present inventors have found that when rib were formed by using a flexible
mold with the photosensitive paste having a viscosity of 26,000, various
defects occurred
due to entrapment of bubbles. The occurrence of defects due to entrapment of
bubbles
was particularly marked in a grid pattern.
The present inventors have found that when a surfactant comprising a
phosphorus
based compound and a sulfonate-based compound are mixed with a photosensitive
paste,
dispersibility of fine particles in the paste is improved while maintaining
high content of
fine ceramic particles, thereby reducing the viscosity to 20,000 cps or less.
Accordingly in one aspect, the present invention relates to a precursor paste,
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comprising:
a photosensitive material;
fine ceramic particles dispersed, as primary particles, in the photosensitive
material; and
a surfactant comprising a phosphorus based compound having at least one
phosphorous atom with at least one -OH group and a sulfonate-based compound
having a
sulfonate group. The precursor paste preferably has a viscosity of 1,500 to
20,000 cps at
22°C.
In another aspect thereof, the present invention relates to a fine structure
comprising a substrate and a pattern of proj ections of predetermined shape
and dimensions
formed on the surface of the substrate, that is formed by photocuring of the
precursor paste
of the present invention.
In still another aspect thereof, the present invention relates to a method of
producing a fine structure comprising a substrate and a pattern of proj
ections of
predetermined shape and dimensions formed on the surface of the substrate,
that
comprises the steps of:
preparing a flexible mold that has a pattern of grooves of shape and
dimensions,
that correspond to the pattern of projections to be formed on the surface of
the substrate;
filling the grooves of the mold with the paste such as by placing the paste in
a
space between the substrate and the groove pattern of the mold;
laminating the mold on the substrate;
irradiating the paste with light of predetermined wavelengths to carry out
photocuring, so as to form the fine structure that comprises the substrate and
the pattern of
projections integrally bonded therewith; and
removing the mold from the fine structure.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a sectional view schematically showing an example of the prior art
PDP to
which the present invention can be also applied.
Fig. 2 is a perspective view showing a back panel for PDP having ribs of the
present invention that is an embodiment of the fine structure of the present
invention.
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Fig. 3 is a perspective view showing one embodiment of the flexible mold used
in
the present invention.
Fig. 4 is a sectional view taken along line 1V-IV of the flexible mold shown
in Fig.
3
Fig. SA-SC are sectional views sequentially showing one method of producing
the
back panel for PDP having ribs of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is directed to a (e.g. photosensitive) ceramic paste
suitable
for use in the production of fine structures such as rib of PDP ribs by
molding the paste
based on photocuring.
The photosensitive ceramic paste includes the following three kinds of
components:
(1) a photosensitive material,
(2) fine ceramic particles dispersed, as primary particles, in the paste, and
(3) a surfactant comprising a phosphorus based compound having at least one
phosphorous atom with at least one -OH group in the molecule and a sulfonate-
based
compound having a sulfonate group in the molecule. The photosensitive ceramic
paste
may optionally contain other additional components.
In the photosensitive ceramic paste of the present invention, a photosensitive
material as a first component may be various photosensitive materials used
generally in a
general-purpose photosensitive paste, but is preferably a photosensitive
material
containing a monomer or oligomer having a (meth)acryl group in the molecule.
Examples of the methacryl group-containing monomer or oligomer suited for
practice of the present invention include, but axe not limited to triethylene
glycol
dimethacrylate, diethylene glycol dimethacrylate, ethylene glycol
dimethacrylate,
1,6-hexanediol dimethacrylate, glycerin dimethacrylate, 2-hydroxy-3-
acryloyloxypropyl
methacrylate, neopentyl glycol dimethacrylate, 1,10-decanediol dimethacrylate,
bisphenol A diglycidyl ether methacrylic acid adduct, and EO adduct
dimethacrylate of
bisphenol A. These monomer or oligomers may be used alone, or two or more
kinds of
them may be used in combination.
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The second component, namely fine ceramic particles, include various fine
ceramic particles that are commonly used for photosensitive paste. Ceramic
materials that
can be advantageously used in the form of fine particles in the embodiments of
the present
invention include, but are not limited to, glass, alumina, titania, zirconia
and silica. Fine
particles of these ceramic materials can be used individually or in a mixture
of two or
more binds. Fine particles of one kind of ceramic material may also be covered
by one or
more thin coatings of another kind of ceramic material or, if necessary, by
polymer
coating instead of ceramic material.
Wlule the fine ceramic particles may have various particle sizes, they have
average
particle size of preferably from about 0.1 to 10 Vim, and more preferably from
about 0.5 to
5.0 Vim, whenused in the formation of ribs or the like is taken into
consideration.
Furthermore, the phosphorus based compound used as a third component
(surfactant) in the photosensitive ceramic paste, together with the
photosensitive resin and
fine ceramic particles, is not specifically limited as far as it is a
phosphorus based
compound having a at least one phosphorous atom with at least one -OH group in
the
molecule (i.e. having at least one phosphorus-based acid group), but is
preferably a
phosphorus based compound represented by the following general formula (I),
(II), (III) or
(1V):
Ry0-P-O_R2
I
OH (1 )
X
R3-O-F-O-R4
I
OH
(II)
X
Rs O~P-O~R6
~- OH m
(III)
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X
R~ O-P-OH
I
OH (IV)
In the above formulas,
Rl to R~ may be the same or different and represent a hydrocarbon group having
1
to 60 carbon atoms, which may optionally contain 1 to 30 heteroatoms, such as
oxygen,
nitrogen, sulfur, and the like,
X represents an oxygen atom or a sulfur atom, and
m represents an integer of 1 to 4.
Typical examples of the phosphorus based compound include, but are not limited
to, phosphorous acid monoalkyl (C1-10) esters and phosphorous acid diall~yl
(C1-10)
esters, such as dibutyl phosphate, butyl phosphate, dimethyl phosphate, methyl
phosphate,
propyl phosphate, dipropyl phosphate, Biphenyl phosphate, phenyl phosphate,
isopropyl
phosphate, diisopropyl phosphate and n-butyl-2-ethylhexyl phospl>ite;
phosphoric acid
monoall~yl (C1-10) esters and phosphoric acid diallcyl (C1-10) esters, such as
dibutyl
phosphate, butyl phosphate, methyl phosphate, propyl phosphate, dipropyl
phosphate,
Biphenyl phosphate, phenyl phosphate, isopropyl phosphate, diisopropyl
phosphate and
butyl-2-ethylhexyl phosphate; and thiophosphate compounds wherein oxygen of
the
above-mentioned phosphate esters is replaced by sulfur. Also, compounds having
an
unsaturated group such as acryl group, methacryl group or vinyl group at the
all~yl moiety
of the phosphorous acid alkyl esters may be used. Furthermore, compounds
having a
phosphate or phosphinate group may be used. More preferable phosphorus based
compound includes a phosphorus based compound having two or more phosphate or
phosphinate groups, for example, alkyldiphosphonic acid such as
hydroxyethylenediphosphonic acid.
The sulfonate-based compound used, as the surfactant, in combination with the
phosphorus based compound is not specifically limited as far as it is a
sulfonate-based
compound having a sulfonate group in the molecule, and examples thereof
include:
sodium allcylbenzenesulfonate, calcium alkylbenzenesulfonate, sodium
allcylnaphthalenesulfonate, naphthalenesulfonic acid-formalin condensate,
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sodium sulfosuccinic acid dialkyl ester, sodium alkyldiphenyl ether
disulfonate and the
like.
For the photosensitive ceramic paste of the present invention, it is necessary
to use
the two kinds of compound described above in combination, as a surfactant.
When these
compounds are combined, a mixing ratio of the phosphorus based compound to the
sulfonate-based compound (weight ratio) is usually within a range from about
99: 1 to 1:
99, and preferably from about 90: 10 to 10: 90. When the mixing ratio is out
of the range
described above, the fine ceramic particles cannot be dispersed to the level
of primary
particles, making it unable to decrease the viscosity to a desired level.
The photosensitive ceramic paste of the present invention has viscosity of
20,000
cps or less, preferably within a range from 2,000 to 10,000 cps as measured at
22°C.
When the viscosity of the paste is decreased by decreasing the content of the
fine glass
particles in the paste, shrinkage during firing increases thus leading to
inevitable problems
such as increasing defects and worsening deformation of ribs. According to the
present
invention, a surfactant having a phosphate group is synergistically employed
in
combination with a surfactant having a sulfonate group. In doing so, it was
unexpectedly
made possible to disperse fine particles of glass or ceramic to the level of
primary particles
in the photosensitive paste. As a result, the viscosity could be decreased to
10,000 cps or
less, for example, for a photosensitive paste containing 80% by weight of fine
glass
particles.
As will be described later in the appended examples, viscosity of a
photosensitive
paste containing 80% by weight of fine glass particles could be decreased only
to a high
value of 26,000 cps when only a phosphorus based compound having a phosphate
group
was added as a surfactant. Further, the viscosity of the photosensitive paste
could be
decreased only to a high value of 35,000 cps when only a sulfonate-based
compound
having a sulfonate group was added as a surfactant. However, in case the
phosphorus
based compound having a phosphate group being employed in combination with a
sulfonate-based compound having a sulfonate group, as exemplified, the
viscosity of the
photosensitive paste could be decreased to as low as 6,000 cps. Further, the
maximum
particle size of the paste of the invention was about 2 to 3 ~,m and fme
particles of glass
were dispersed as the primary particles (average particle size of about 2 to 3
~,m), making
a great contribution to the effects of the present invention.
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The paste described herein was also found to have improved shelf life. For
example, the paste of the invention was left to stand at 22°C for two
months and found not
to deteriorate as indicated by gelation.
The content of the fine ceramic particles in the photosensitive ceramic paste
of the
present invention is usually within a range from 60 to 90% by weight, and
preferably from
about 70 to 85% by weight. When the content of the fine ceramic particles in
the paste is
out of the range described above, it can adversely effect the production and
characteristics
of the fine structure. Adverse effects such as faulty application of the
paste, damage or
defect of the fine structure such as ribs and difficulty of releasing from the
mold may be
observed.
The photosensitive ceramic paste of the present invention optionally contains
additives, which are commonly used in a general-purpose photosensitive paste,
in addition
to the above-mentioned components. Suitable additives include binders,
photopolymerization initiators, diluents, ultraviolet absorbers, sensitizers,
auxiliary
sensitizers, polymerization ii~lubitors, plasticizers, thickeners and organic
solvents.
The photosensitive ceramic paste of the present invention can have various
compositions as far as it satisfies the above-mentioned constituent features,
and preferably
has a composition comprising:
5 to 15 parts by weight of a photosensitive resin,
60 to 90 parts by weight of fme ceramic particles,
0.1 to 1.0 parts by weight of a surfactant made of a phosphorus based
compound,
0.1 to 1.0 parts by weight of a surfactant made of a sulfonate-based compound,
5 to 15 parts by weight of a diluent, and
0.02 to 0.25 parts by weight of a photopolymerization initiator.
The ceramic paste having such a composition may contain optional additives in
commonly employed amounts.
The photosensitive ceramic paste of the present invention is preferably cured
by
photocuring through irradiation with light via a flexible mold having a
pattern of grooves
of predetermined shape and dimensions being formed on the surface thereof, and
is
therefore useful as the fine structure-providing precursor paste. A typical
example of the
fine structure is ribs formed on a baclc panel of PDP. The pattern of grooves
of the
flexible mold for mal~ing the ribs on the back panel of PDP may be a straight
pattern or a
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plurality of grooves arranged at equal intervals substantially in parallel to
each other, but is
preferably a grid pattern of a plurality of grooves arranged at equal
intervals substantially
in parallel to each other and crossing each other. In short, the ribs of the
back panel of
PDP may be formed in either a straight pattern or a grid pattern, although
grid pattern is
preferable.
The present invention provides a fine structure having a pattern of proj
ections of
predetermined shape and dimensions formed on the surface of a substrate. The
fme
structure of the present invention is preferably ribs of a back panel of PDP.
In the back
panel of PDP, the pattern of proj ecting ribs may be either a straight pattern
of a plurality of
ribs arranged at equal intervals substantially in parallel to each other, or a
grid pattern of a
plurality of ribs arranged at equal intervals substantially in parallel to
each other and
crossing each other, but is preferably a grid pattern of ribs.
Also the present invention provides a method of producing a fine structure
having
a pattern of projections of predetermined shape and dimensions formed on the
surface of a
substrate. The method of the present invention comprises the steps of
preparing a flexible mold that has a pattern of grooves of shape and
dimensions,
which correspond to the pattern of projections, formed on the surface thereof;
placing the photosensitive ceramic paste (fine structure precursor paste) of
the
present invention in a space between the substrate and the grooves pattern of
the mold,
filling the grooves of the mold with the ceramic paste and laminating the mold
on the
substrate;
irradiating the ceramic paste with light of predetermined wavelengths to carry
out
photocuring, so as to form the fine structure comprising the substrate and the
pattern of
projections integrally bonded therewith; and
removing the mold from the fine structure.
As described previously, the fine structure is preferably ribs of the back
panel of
PDP. Therefore, the method of the present invention preferably further
includes the step
of forming a set of address electrodes at equal intervals substantially in
parallel to and
independently from each other on the surface of the substrate.
The mold used in the practice of the present invention is preferably a
flexible mold
comprising a support and a molding layer that is provided on the support and
has a pattern
of grooves of predetermined shape and dimensions, which correspond to the
pattern of
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projection, formed on the surface thereof. The flexible mold will be described
in detail
later.
The practice of the present invention will be described in more detail below
with
reference to the accompanying drawings.
Fig. 2 shows ribs 54 of PDP that is a typical example of the fine structure of
the
present invention. The ribs 54 of PDP are formed on the back panel glass
substrate 51 so
as to constitute the back panel of the PDP, and can be advantageously used
when
incorporated in the PDP 50 as shown in Fig. 1. While the ribs 54 shown are
formed in a
straight pattern, a grid pattern of ribs that cross each other at right angles
is also included
in the scope of the present invention, and photosensitive ceramic paste of the
present
invention can fully achieve its excellent effects when the ribs are formed in
a grid pattern.
Intervals c (cell pitch) of the ribs 54 shoran in the drawing may be changed
in
accordance to the screen size and/or other factors, but usually within a range
from about
150 to 400 Vim. Ribs are generally required to be free of defects and to have
high
dimensional accuracy. As to the dimensional accuracy, the ribs are required to
be formed
at the predetermined positions corresponding to the address electrodes with
almost no
deviation allowing tolerance of several tens of micrometers. A positional
error of more
than several tens of micrometers will have adverse effect on the condition of
emitting
visible light thus making satisfactory spontaneous light emission impossible.
As larger
screen sizes are becoming more popular, accuracy of rib pitch poses a serious
problem.
When the ribs 54 are viewed as a whole, accuracy of several tens of ppm is
required for the total pitch R (distance between outermost ribs: although only
five ribs are
shown in the drawing, actually there are about 3,000 ribs) of the ribs, while
it varies a little
depending on the substrate size and the rib shape. While the flexible mold
comprising the
support and the molding layer that is supported by the support and has a
pattern of grooves
is advantageously used in the practice of the present invention, accuracy of
several tens of
ppm is required for the total pitch R (distance between outermost grooves) of
the mold,
too. According to the present invention, such problems of dimensional accuracy
can also
be solved.
Although any flexible mold can advantageously be used in the practice of the
present invention, the mold preferably comprises the support comprising a
plastic film,
and the molding layer having a pattern of grooves (groove portion) formed by
molding of
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a photocurable resin on one side of the support.
The support suited for practice of the present invention is a film made of a
plastic
material. Examples of the plastic material suited for use as the support
include, but are not
limited to, polyethylene terephthalate (PET), polyethylene naphthalate (PEN),
stretched
polypropylene, polycarbonate and triacetate. Among these plastic materials,
PET film is
useful as the support and, for example, polyester film such as TetoronTM film
can be
advantageously used as the support. These plastic films may be used as a
single-layer
film, or two or more kinds of them may be used in combination as a mufti-layer
film.
While the plastic film may have various thicknesses depending on the
constitutions
of the mold and the PDP, the thickness is usually within a range from 0.01 to
1.0 mm, and
preferably within a range from 0.1 to 0.4 mm. When the support has thickness
out of this
range, it becomes difficult to handle. Thus, a tlucker support can be
advantageous.
In addition to the support described above, the flexible mold has a molding
layer
formed thereon. As will be described in detail below, the molding layer has
the pattern of
grooves of predetermined shape and dimensions, which correspond to the pattern
of
projections such as the ribs or other fine structure of the PDP back panel to
be produced by
using the mold, being formed on the surface thereof and may also be called the
shape
forming layer. The molding layer normally consists of a single layer, but may
also be
formed in a mufti-layer structure from two or more binds of material having
different
properties if necessary. Both the support and the molding layer are preferably
transparent,
when it is taken into consideration that a photocurable molding material is
used.
Now, the constitution of the flexible mold will be described below with
reference
to Figs. 3 and 4. Constitution of the ribs formed in grid pattern by
photocuring using the
flexible mold will also be easily understood from the following description.
Fig. 3 is a perspective view schematically showing a part of a preferable
embodiment of the flexible mold, and Fig. 4 is a sectional view taken along
line IV-IV of
Fig. 3. As will be seen from these drawings, the flexible mold 10 is not
designed for the
production of the back glass substrate 51 having straight pattern of ribs
comprising a
plurality of ribs 54 arranged in parallel to each other shown in Fig. 2. It is
for the produce
of the back glass substrate having grid pattern of ribs comprising a plurality
of ribs
arranged substantially in parallel to each other while crossing, though not
shown. The
photosensitive ceramic paste of the present invention is particularly useful
in producing
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the back glass substrate having grid pattern of ribs.
The flexible mold 10 has the pattern of grooves having predetermined shape and
dimensions formed on the surface thereof, as illustrated. The pattern of
grooves
constituted from a plurality of grooves 4 that are arranged at equal intervals
substantially
in parallel to each other while crossing. As such, while the flexible mold 10
can be used
in the production of other fine structures, this constitution of the grooves
formed on the
surface in grid pattern is particularly useful in forming the PDP ribs having
grid pattern of
projections. The flexible mold 10 may have additional layer or the
constituting layers
thereof may be processed as required, but the mold is basically constituted
from the
support 1 and the molding layer 11 formed thereon having the groove portion 4
as shown
in Fig. 3.
The molding layer 11 is preferably made of a curable material. The curable
material is a thermocurable material or a photocurable material. Particularly,
the
photocurable material is useful because it can be cured within a comparatively
short time
without requiring a long and large heating furnace for formation of the
molding layer. The
photocurable material is preferably a photocurable monomer or oligomer, and
more
preferably an acrylic monomer or oligomer. The curable material can contain
optional
additives. Suitable additives include polymerization initiators (for example,
photoinitiators) and antistatic agents.
Examples of the acrylic monomer suited for formation of the molding layer
include, but are not limited to, urethane acrylate, polyether acrylate,
acrylamide,
acrylonitrile, acrylic acid and acrylate ester. Examples of the acrylic
monomer suited for
formation of the molding layer include, but are not limited to, urethane
acrylate oligomer
and epoxy acrylate oligomer. Particularly, the urethane acrylate and oligomer
thereof can
provide a flexible and tough cured article after curing, and can also
contribute to an
improvement in productivity of the mold because of very large curing rate
among
acrylates. Furthermore, when using these acrylic monomers or oligomers, the
molding
layer becomes optically transparent. Therefore, the flexible mold comprising
such a
molding layer enables the use of the photocurable molding material when the
fine
structure such as PDP ribs is produced. These acrylic monomers or oligomers
may be
used alone, or two or more kinds of them may be optionally used in
combination.
As already mentioned, the support 1 carrying the molding layer 11 is
preferably a
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plastic film of which thickness is usually within a range from about 0.05 to
1.0 mm. The
support is preferably optically transparent. When the support is optically
transparent,
since light irradiated for curing can transmit through the support, the
molding layer can be
formed by using a photocurable molding material. A typical example of
transparent
support is as described above.
When the flexible mold described above and the fine ceramic structure of the
present invention are combined in the molding operation, various fine
structures can be
produced according to the mold and properties of the paste. For example, use
of the
flexible mold shown in Figs. 3 and 4 enables it to produce the ribs of PDP
having grid
pattern with high aspect ratio and high accuracy without requiring skills nor
causing
defects in the ribs. Use of the flexible mold also enables it to easily
produce PDP of large
screen having such a rib structure by simply using a laminate roll instead of
vacuum
equipment and/or a complicated process.
The present invention also provides the fine structure and the method of
producing
the same. While the fine structure may be formed in various structures,
typical example
thereof is the rib portion of the substrate (back panel) of PDP wherein the
ribs are formed
on a flat glass sheet. Now the method of producing the PDP substrate having
the grid
pattern of ribs by using the flexible mold shown in Figs. 3 and 4 will be
described below
with reference to Fig. 5. The producing apparatus shown in Figs. 1 to 3 of
Japanese
Unexamined Patent Publication (Kolcai) No. 2001-191345, for example, can be
advantageously used for the practice of the present invention.
Although not illustrated, a flat glass sheet having electrodes disposed
thereon at
equal intervals in parallel to each other is prepared in advance and is set on
a surface plate.
Then as shown in Fig. 5(A), the flexible mold 10 of the present invention
having the
pattern of grooves is placed at a predetermined position on the flat glass
sheet 31, and
alignment of the flat glass sheet 31 and the mold 10 is carried out. Since the
mold 10 is
transparent, alignment of the flat glass sheet 31 and the electrodes can be
carned out
easily. More specifically, the alignment is carried out either under visual
observation or
by using a sensor such as CCD camera so as to make the groove portion of the
mold 10
and electrodes on the flat glass sheet 31 parallel to each other. At this
time, the mold 10
and distance between adjacent electrodes on the flat glass sheet 31 may be
made equal by
controlling the temperature and humidity, as required. This is because the
mold 10 and the
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flat glass sheet 31 expand or shrink with different rates with temperature and
humidity.
Therefore, when alignment of the flat glass sheet 31 and the mold 10 has been
completed,
temperature aazd humidity at that time are controlled constant. Such
controlling method is
particularly effective for producing the PDP substrate of large surface area.
Then a laminate roll 23 is placed on one edge of the mold 10. The laminate
roll 23
is preferably a rubber roll. The one edge of the mold 10 is preferably fixed
on the flat
glass sheet 31. In this way, alignment of the flat glass sheet 31 (with
electrodes) and the
mold 10 may be maintained during subsequent operations.
Then the other free edge of the mold 10 is lifted by a holder (not shown) and
is
moved to above the laminate roll 23 so as to expose the flat glass sheet 31.
At this time,
care is exercised so as not to apply tension to the mold 10, so as to prevent
the mold 10
from being wrinkled and to maintain the aligned positions of the flat glass
sheet 31 and the
mold 10. But other means may be employed as long as the aligned positions can
be
maintained. With tlus method, since the mold 10 has elasticity, even if the
mold 10 is
curled up as shown in the drawing, the mold 10 returns exactly to the aligned
position
when laminated thereafter.
Then a predetermined amount of the photosensitive paste 33 required to form
the
ribs is supplied onto the flat glass sheet 31. The photosensitive paste 33
comprises the
photosensitive ceramic paste of the present invention described previously.
The
photosensitive ceramic paste 33 may be supplied, for example, by means of a
paste hopper
equipped with a nozzle.
When applying the method shown in the drawing, the photosensitive ceramic
paste
33 is supplied onto the flat glass sheet 31 not evenly over the surface.
Instead, the rib
precursor 33 is supplied only to a position on the flat glass sheet 31 near
the laminate roll
23 as shown in Fig. 5(A). This is because the photosensitive ceramic paste 33
can be
spread uniformly over the flat glass sheet 31 as the laminate roll 23 moves
over the mold
10 in the process to be described later. The photosensitive ceramic paste 33
has viscosity
preferably within a range from 2,000 to 10,000 cps in order to carry out this
operation
smoothly as well. However, method of supplying the photosensitive ceramic
paste is not
limited to that described above. For example, the photosensitive ceramic paste
may also
be applied so as to coat the entire surface of the flat glass sheet, although
not shown.
Then the laminate roll 23 is moved over the mold 10 at a predetermined speed
by a
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WO 2005/019934 PCT/US2004/026701
motor (not shown) as indicated with an arrow in Fig. 5(A). While the laminate
roll 23 is
moving over the mold 10, a pressure is applied onto the mold 10 progressively
from one
edge to the other edge thereof by the gravity of the laminate roll 23, so as
to spread the
photosensitive ceramic paste 33 over the space between the flat glass sheet 31
and the
mold 10 thereby filling the grooves of the mold 10 with the paste. That is,
the
photosensitive ceramic paste 33 fills the grooves successively while replacing
the air
therein. At this time, thickness of the photosensitive ceramic paste can be
controlled
within a range from several micrometers to several tens of micrometers by
adjusting the
viscosity of the ceramic paste, or the diameter, weight or traveling speed of
the laminate
roll.
Also according to the method shown in the drawing, the grooves of the mold
also
serve as channels for air flow. Even when air is captured in the grooves, the
air can be
efficiently purged to the outside of the mold when the pressure is applied as
described
above. As a result, with this method, bubbles can be prevented from remaining
in the
grooves even when the photosensitive ceramic paste is supplied under the
atmospheric
pressure. In other words, necessity to reduce the pressure can be eliminated
when
applying the photosensitive ceramic paste. It needs not to say that pressure
may be
reduced so as to malce the removal of bubbles easier.
Then the photosensitive ceramic paste is cured. In case the ceramic paste 33
that is
spread over the flat glass sheet 31 is photocurable; as shown in Fig. 5(B),
the laminate of
the flat glass sheet 31 and the mold 10 is put into a light irradiating
apparatus (not shown)
to irradiate the ceramic paste 33 with ultraviolet rays (LTL) via the flat
glass sheet 31 and
the mold 10. Thus ribs are made of the photosensitive ceramic paste.
Last, the flat glass sheet 31 and the mold 10 are taken out of the light
irradiating
apparatus with the ribs 34 bonded onto the flat glass sheet 31, and the mold
10 is removed
as shown in Fig. 5(C). The mold typically has good release properties.
However, a
release coating may be optionally applied to the mold to aid in easy removal
of the mold
10 with less force without damaging the ribs 34 that adheres to the flat glass
sheet 31. Of
course, no major apparatus is required for this mold releasing operation.
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EXAMPLES
Example 1
Preparation of photosensitive glass paste:
To prepare a glass paste, the following materials were prepared in the
following
amount.
Photocurable oligomer: bisphenol A diglycidyl methacrylate acid adduct 318.5 g
(manufactured by Kyoeisha Co., Ltd.)
Photocurable monomer: triethylene glycol dimethacrylate (manufactured by 136.5
g
Wako Pure Chemical Industries, Ltd.)
Diluent: 1,3-butanediol (manufactured by Wako Pure Chemical Industries, Ltd.)
455.0 g
Photocuring initiator: bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide
(manufactured by Ciba Speciality Chemicals under the trade name of "Irgacure
6.4 g
819")
Fine ceramic particles: mixed powder of lead glass and ceramic (manufactured
4093.0 g
by Asahi Glass Co. under the trade name of "RFW-030")
Phosphot-us based surfactant: phosphate propoxyalkyl polyol (manufactured by
25,3 g
3M under the trade name of "POCA")
Sulfonate-based surfactant: sodium dodecylbenzenesulfonate (manufactured by
25,3 g
Kao Co. under the trade name of "NeoPelex #25")
All these materials were put into an attrition mill and dispersed at
30°C for one
hour with zirconia balls having diameter of 7 mm used as dispersion media.
Upon completion of the dispersing process, the paste was taken out of the
attriter
and was left to stand at 22°C for a whole day and night. Then viscosity
of the paste was
measured with a Broolcfield B viscometer, with shaft #5 and rotation speed of
20 rpm
employed as the measuring conditions. The paste showed viscosity of 6,000 cps.
Production of PDP back panel:
A flexible resin mold having 2593 ribs, each rib being 200 ~.m in height, 100
~,m
in width at the top, and 540 mm in length, at a 360 ~.m pitch was made for the
production
of PDP back panel.
A PDP glass substrate was coated with the photosensitive ceramic paste that
was
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WO 2005/019934 PCT/US2004/026701
made as described above to a thickness of about 100 pm with a coating blade.
Then the
flexible mold was laminated onto the glass substrate coated with the glass
paste, while
flexing the mold and making alignment. A laminate roll 200 mm in diameter and
100 kg
in weight was moved at a speed of 40 mm per second. Pressure applied to the
mold was
generated only by the weight of the laminate roll.
The mold laminated onto the glass substrate was irradiated on both sides of
mold
and glass substrate with light having wavelengths from 400 to 450 nm for 30
seconds
using an array of fluorescent lamps produced by Phillips Corp. Thus the
photosensitive
glass paste was cured and turned into ribs. The glass substrate with the ribs
formed
thereon was removed from the mold, and the glass substrate with the ribs was
obtained.
Total pitch (distance between outermost ribs) was measured at five points on
the
mold used in the molding operation and the glass substrate that was obtained,
with the
results shown in Table 1.
Table 1
Measuring pointResin mold ~b Difference between
mold
and rib
1 933.1.19 mm 933.112 mm -0.007 mm
2 933.121 mm 933.117 mm -0.004 mm
3 933.121 mm 933.122 mm 0.001 nun
4 933.121 mm 933.125 mm 0.004 mm
5 933.123 mm 933.122 mm -0.001 mm
As will be understood from the measurement results shown in Table 1, the ribs
made by using the phosphorus based surfactant and sulfonate-based surfactant
in the paste
according to the present invention showed dimensions almost identical with
those of the
mold, indicating that the ribs were formed with high dimensional accuracy.
The glass substrate with the ribs formed thereon was then fired at
550°C for one
hour to remove organic components contained in the paste by combustion,
thereby to form
the ribs made of glass components. Upon observation of the ribs formed on the
back panel
with an optical microscope, no defect was detected.
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Comparative Example 1
The process described in Example 1 was conducted, except for using 50.6 g of
phosphorus based surfactant (phosphate propoxyalkyl polyol) instead of the
combination
of phosphorus based surfactant and sulfonate-based surfactant for the purpose
of
comparison, when mal~ing the photosensitive ceramic paste. B viscosity of the
paste thus
obtained was 26,000 cps (shaft #5, 20 rpm).
Then a glass substrate having ribs formed thereon was made in the process
described in Example 1, using photosensitive ceramic paste prepared as
described above.
Since the glass paste had high viscosity of 26,000 cps in this example,
greater pressure
was applied when laminating the mold onto the glass substrate coated with the
glass paste.
Specifically, a laminate roll 200 mm in diameter and 250 kg in weight was
moved at a
speed of 20 mm per second. The glass substrate with the ribs formed thereon
was
removed from the mold, and the glass substrate having the ribs was obtained.
Total pitch (distance between outermost ribs) of the ribs was measured at five
points on the mold used in the molding operation and the glass substrate that
was obtained,
with the results shown in Table 2.
Table 2
Measuring pointResin mold ~b Difference between
mold
and rib
1 933.119 mm 933.114 mm -0.005 mm
2 933.121 rrnn 933.136 mm 0.015 mm
3 933.121 mm 933.153 mm 0.032 mm
4 933.121 mm 933.171 mm 0.050 mm
5 933.123 mtn 933.191 mm 0.068 mm
As will be understood from the measurement results shown in Table 2, the ribs
made by using the paste containing only phosphorus based surfactant showed
difference in
dimension from the mold, about 70 ~,m at the maximum. Ribs of high dimensional
accuracy could not be easily formed in this example.
The glass substrate with the ribs formed thereon was then fired at
550°C for one
hour to remove organic components contained in the paste by combustion,
thereby to form
the ribs made of glass components. Upon observation of the ribs formed on the
back panel
with an optical microscope, many defects were detected.
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Comparative Example 2
The process described in Example 1 was conducted, except for using 50.6 g of
sulfonate-based surfactant (sodium dodecylbenzenesulfonate) instead of the
combination
of phosphorus based surfactant and sulfonate-based surfactant for the purpose
of
comparison, when mal~ing the photosensitive ceramic paste. B viscosity of the
paste thus
obtained was 35,000 cps (shaft #5, 20 rpm).
Then a glass substrate having ribs formed thereon was made in the process
described in Example l, using the photosensitive ceramic paste prepared as
described
above. Since the glass paste had high viscosity of 35,000 cps in this example,
greater
pressure was applied when laminating the mold onto the glass substrate coated
with the
glass paste. Specifically, a laminate roll 200 mm in diameter and 250 kg in
weight was
moved at a speed of 10 mm per second. The glass substrate with the ribs formed
thereon
was removed from the mold, and the glass substrate having the ribs was
obtained.
Total pitch (distance between outermost ribs) of the ribs was measured at five
points on the mold used in the molding operation and the glass substrate that
was obtained.
Similar to Comparative Example 1, the measurements showed that the ribs had
difference
in dimension from the mold, about 100 ~,m at the maximum. To sum up, ribs of
high
dimensional accuracy could not be formed in this example.
The glass substrate with the ribs formed thereon was then fired at
550°C for one
hour to remove organic components contained in the paste by combustion,
thereby to form
the ribs made of glass components. Upon observation of the ribs formed on the
back panel
with an optical microscope, many defects were detected.
19
