U.S. patent application number 11/846784 was filed with the patent office on 2009-03-05 for method of forming microstructures on a substrate and a microstructured assembly used for same.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Takaki Sugimoto, Chikafumi Yokoyama.
Application Number | 20090061116 11/846784 |
Document ID | / |
Family ID | 34550565 |
Filed Date | 2009-03-05 |
United States Patent
Application |
20090061116 |
Kind Code |
A1 |
Yokoyama; Chikafumi ; et
al. |
March 5, 2009 |
METHOD OF FORMING MICROSTRUCTURES ON A SUBSTRATE AND A
MICROSTRUCTURED ASSEMBLY USED FOR SAME
Abstract
A method of forming microstructures on a substrate is disclosed.
A microstructured assembly that may be used in the method for
forming microstructures on a substrate is also disclosed. The
methods and assemblies of the present disclosure can reduce the
amount of air entrapped in barrier ribs formed on substrates used
in Plasma Display devices.
Inventors: |
Yokoyama; Chikafumi;
(Zama-shi, JP) ; Sugimoto; Takaki; (Tokyo,
JP) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
34550565 |
Appl. No.: |
11/846784 |
Filed: |
August 29, 2007 |
Current U.S.
Class: |
428/1.21 ;
425/385 |
Current CPC
Class: |
H01J 9/242 20130101;
H01J 11/36 20130101; H01J 2211/36 20130101; B29C 33/10 20130101;
Y10T 428/24355 20150115; H01J 2211/361 20130101; Y10T 428/1009
20150115; H01J 11/12 20130101; C03C 17/008 20130101; C03C 2218/119
20130101; B29L 2031/3475 20130101; B32B 17/06 20130101; B29C 33/424
20130101; C09K 2323/021 20200801; Y10T 428/24628 20150115 |
Class at
Publication: |
428/1.21 ;
425/385 |
International
Class: |
C09K 19/02 20060101
C09K019/02 |
Claims
1. A flexible mold suitable for molding a lattice pattern, wherein
the lattice pattern comprises a first set of ribs aligned in the
first direction and a second set of ribs aligned in a second
direction substantially orthogonal to the first direction, wherein
the first set of ribs comprises a pitch of less than 500 .mu.m, the
ribs of each set have an average width, and the average width of
the second set of ribs to the average width of the first set of
ribs has a ratio of at least 1.5.
2. The flexible mold of claim 1, wherein the pitch of the first set
of ribs is less than 300 .mu.m.
3. The flexible mold of claim 1 wherein the first and second set of
ribs have an average width ranging from 20 .mu.m to 50 .mu.m.
4. The flexible mold of claim 1 wherein the first and second set of
ribs have heights of about 120 .mu.m to 140 .mu.m.
5. The flexible mold of claim 1 wherein the first and second set of
ribs have widths of about 20 .mu.m to 75 .mu.m.
6. The flexible mold of claim 1 wherein the mold is a transparent
plastic mold.
7. The flexible mold of claim 1 wherein the mold is a flexible
polymer sheet having a smooth surface and an opposing
microstructured surface.
8. A plasma display panel comprising barrier ribs having a lattice
pattern, wherein the lattice pattern comprises a first set of ribs
aligned in the first direction and a second set of ribs aligned in
a second direction substantially orthogonal to the first direction,
wherein the first set of ribs comprises a pitch of less than 500
.mu.m, the ribs of each set have an average width, and the average
width of the second set of ribs to the average width of the first
set of ribs has a ratio of at least 1.5.
9. The plasma display panel of claim 8, wherein the pitch of the
first set of ribs is less than 300 .mu.m.
10. The plasma display panel of claim 8 wherein the first and
second set of ribs have an average width ranging from 20 .mu.m to
50 .mu.m.
11. The plasma display panel of claim 8 wherein the first and
second set of ribs have heights of about 120 .mu.m to 140
.mu.m.
12. The plasma display panel of claim 8 wherein the first and
second set of ribs have widths of about 20 .mu.m to 75 .mu.m.
13. The plasma display panel of claim 8, wherein a plurality of
ribs of the first set of ribs are connected by intervening land
regions, and further wherein the intervening land regions comprise
a substantially uniform center thickness.
14. The plasma display panel of claim 8, wherein a plurality of
ribs of the second set of ribs are connected by intervening land
regions, and further wherein the intervening land regions comprise
a substantially uniform center thickness.
15. The plasma display panel of claim 8, wherein the ribs comprises
a cured and fired ceramic material.
Description
[0001] The present disclosure generally relates to microstructured
assemblies. More specifically, the present disclosure relates to
methods of forming microstructures on a substrate that are
substantially devoid of bubbles.
BACKGROUND
[0002] Advancements in display technology, including the
development of plasma display panels (PDPs) and plasma addressed
liquid crystal (PALC) displays, have led to an interest in forming
electrically-insulating ceramic barrier ribs on glass substrates.
The ceramic barrier ribs separate cells in which an inert gas can
be excited by an electric field applied between opposing
electrodes. The gas discharge emits ultraviolet (uv) radiation
within the cell. In the case of PDPs, the interior of the cell is
coated with a phosphor that gives off red, green, or blue visible
light when excited by uv radiation. The size of the cells
determines the size of the picture elements (pixels) in the
display. PDPs and PALC displays can be used, for example, as the
displays for high definition televisions (HDTV) or other digital
electronic display devices.
[0003] One way in which ceramic barrier ribs can be formed on glass
substrates is by direct molding, which involves laminating a planar
rigid mold onto a substrate with a glass- or ceramic-forming
composition disposed therebetween. The glass- or ceramic-forming
composition is then solidified and the mold is removed. Finally,
the barrier ribs are fused or sintered by firing at a temperature
of about 550.degree. C. to about 1600.degree. C. The glass- or
ceramic-forming composition has micrometer-sized particles of glass
frit dispersed in an organic binder. The use of an organic binder
allows barrier ribs to be solidified in a green state so that
firing fuses the glass particles in position on the substrate.
However, in applications such as PDP substrates, highly precise and
uniform barrier ribs with few or no defects or fractures are
required. These requirements can pose challenges, especially during
removal of the rigid mold from the green state ribs.
[0004] PDP ribs are typically arranged in one of two pattern types.
One type is referred to as a "straight pattern." This straight
pattern is simple and can be relatively easily manufactured on a
large scale.
[0005] A flexible resin mold can be used to mold ribs having the
straight pattern. The resin mold is manufactured in the following
way. First, a photosensitive resin is filled into a metal master
mold having the same pattern and the same shape as those of the rib
pattern to be manufactured. Next, this photosensitive resin is
covered with a plastic film and is cured to integrate the
photosensitive resin after curing with the film. The film is then
released with the photosensitive resin from the metal master mold
to form a flexible resin mold.
[0006] Another rib pattern type is referred to as a "lattice
pattern." The lattice pattern can be used to improve the vertical
resolution of a PDP compared to the straight pattern, because
ultraviolet rays from the discharge display cell are better
confined and are hence less likely to leak to adjacent cells. In
addition, the phosphors can be applied to a relatively greater area
of the discharge display cell when lattice pattern ribs are
employed.
[0007] Methods have previously been described that enable molding
and formation of ceramic microstructures such as straight or
lattice rib patterns on a patterned substrate.
[0008] For example, U.S. Pat. No. 6,247,986 B1 to Chiu et al.,
entitled METHOD FOR PRECISE MOLDING AND ALIGNMENT OF STRUCTURES ON
A 20 SUBSTRATE USING A STRETCHABLE MOLD, and U.S. Pat. No.
7,033,534 to Chiu et al., entitled METHOD OF FORMING
MICROSTRUCTURES ON A SUBSTRATE USING A MOLD, describe the molding
and aligning of ceramic barrier rib microstructures on an
electrode-patterned substrate. Such ceramic barrier rib
microstructures may be particularly useful in electronic displays,
such as PDPs and PALC displays, in which pixels are addressed or
illuminated via plasma generation between opposing substrates.
[0009] Although a mold can be used to manufacture ribs having the
lattice pattern, the removal of a rigid mold typically results in
damage to the ribs. A flexible mold as described herein can be
applied to molding lattice pattern ribs so that damage to the ribs
may be avoided. According to existing molding technology, however,
it is difficult to manufacture a mold that eliminates the problem
of rib damage upon mold removal. In addition to problems with rib
damage upon de-molding, it is preferred not to entrap air bubbles
within the mold. Large air bubbles can result in defects large
enough to effectively interrupt the continuity of the ribs. Small
air bubbles are not as disruptive, but their presence is not
preferred.
[0010] For the lattice pattern, damage to the lateral ribs (those
lying perpendicular to the axis of removal of the flexible mold) is
a problem. In addition, the rib material needs to have a
sufficiently high viscosity such that it maintains the rib shape
after removal of the mold. However, since high viscosity material
has low flowability, air bubbles in lateral grooves of the mold are
difficult to eliminate completely.
SUMMARY
[0011] In general, the invention is directed to a method for
forming microstructures on a substrate. The invention is further
directed to a microstructured assembly that may be used with the
disclosed method.
[0012] One advantage of this disclosure is that air bubbles can be
removed using a method that employs only one application of
pressure from a roller or the like in only the first direction, in
contrast to a two-step application method which would also include
a second application of pressure from a roller or the like
traveling in the second direction. It is another advantage of this
invention that air bubbles can be so removed using techniques that
do not use vacuum devices. For example, vacuum press molding
devices limit the size of the panels that can be processed to only
at most several centimeters. The techniques described herein, on
the other hand, can produce rib patterns on large substrates.
[0013] In one aspect, the present disclosure provides a method of
forming microstructures on a substrate. The method includes
disposing a curable material on a substrate, where the curable
material includes a viscosity of less than 12,000 cps. The method
further includes contacting the curable material with a flexible
mold starting at a first end of the substrate and proceeding at a
substantially uniform contact speed in a first direction and
applying a substantially uniform contact pressure. In addition, the
method includes forming the curable material, using the mold, into
a lattice pattern, where the lattice pattern includes a first set
of ribs aligned in the first direction and a second set of ribs
aligned in a second direction substantially orthogonal to the first
direction, where the first set of ribs includes a pitch of less
than 500 .mu.m. The method further includes curing the curable
material, and removing the mold.
[0014] In another aspect, the present disclosure provides a
microstructured assembly that includes a substrate, and a flexible
mold including a microstructured surface that opposes a surface of
the substrate. The assembly further includes a curable material
disposed between the substrate and the microstructured surface of
the flexible mold, where the microstructured surface of the mold is
configured to impart a lattice pattern into the curable material.
The lattice pattern includes a first set of ribs aligned in a first
direction and a second set of ribs aligned in a second direction
substantially orthogonal to the first direction, where the first
set of ribs includes a pitch of less than 500 .mu.m. The curable
material includes a viscosity of less than 12,000 cps. In addition,
the curable material is substantially devoid of large bubbles.
[0015] The above summary of the present invention is not intended
to describe each disclosed embodiment or every implementation of
the present invention. The Figures and the detailed description
which follow more particularly exemplify these embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic diagram of one embodiment of a lattice
pattern barrier rib assembly.
[0017] FIGS. 2a-e are schematic diagrams of one embodiment of a
method of forming microstructures on a substrate.
[0018] FIG. 3 is a schematic diagram of a path taken by air bubbles
as they are removed from a curable material.
[0019] FIGS. 4a-c are schematic diagrams of one embodiment of a
flexible mold.
[0020] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the
invention.
DETAILED DESCRIPTION
[0021] FIG. 1 is a schematic diagram of one embodiment of a lattice
pattern barrier rib assembly 10. The assembly 10 includes a
substrate 12 and a lattice pattern 20 disposed on a major surface
14 of the substrate 12. The lattice pattern 20 includes a first set
of ribs 22 aligned in a first direction 16 and a second set of ribs
24 aligned in a second direction 18. The first direction 16 and the
second direction 18 are substantially orthogonal.
[0022] In general, plasma display panels (PDPs) can include various
substrate elements. The back substrate assembly (e.g., assembly
10), which can be oriented away from the viewer, can include a back
substrate (e.g., substrate 12) with independently addressable
parallel electrodes (not shown in FIG. 1) formed on or in a major
surface of the back substrate. The back substrate can be formed
from a variety of compositions, e.g., glass. Microstructures (e.g.,
lattice pattern 20) are formed on a major surface of the back
substrate and include barrier rib portions that are positioned
between electrodes and separate areas in which red (R), green (G),
and blue (B) phosphors are deposited. PDPs can also include a front
substrate assembly that includes a glass substrate and a set of
independently addressable parallel electrodes. These front
electrodes, also called sustain electrodes, are oriented
orthogonally to the back electrodes, also referred to as address
electrodes.
[0023] In a completed display, the area between the front and back
substrate assemblies can be filled with an inert gas. To light up a
pixel, an electric field is applied between crossed sustain and
address electrodes with enough strength to excite the inert gas
atoms therebetween. The excited inert gas atoms emit uv radiation,
which causes the phosphor to emit red, green, or blue visible
light.
[0024] It may be preferred that the back substrate is a transparent
glass substrate. Typically, for PDP applications, the back
substrate is made of soda lime glass that is optionally
substantially free of alkali metals. The temperatures reached
during processing can cause migration of the electrode material in
the presence of alkali metal in the substrate. This migration can
result in conductive pathways between electrodes, thereby shorting
out adjacent electrodes or causing undesirable electrical
interference between electrodes known as "crosstalk." The front
substrate is typically a transparent glass substrate that can have
the same or about the same coefficient of thermal expansion as that
of the back substrate.
[0025] Electrodes are strips of conductive material. The electrodes
are formed of a conductive material, e.g., copper, aluminum, or a
silver-containing conductive frit. The electrodes can also be a
transparent conductive material, such as indium tin oxide,
especially in cases where it is desirable to have a transparent
display panel. The electrodes are patterned on the back substrate
and front substrate. For example, the electrodes can be formed as
parallel strips spaced about 120 .mu.m to 360 .mu.m apart, having
widths of about 50 .mu.m to 75 .mu.m, thicknesses of about 2 .mu.m
to 15 .mu.m, and lengths that span the entire active display area
that can range from a few centimeters to several tens of
centimeters. In some instances, the widths of the electrodes can be
narrower than 50 .mu.m or wider than 75 .mu.m, depending on the
architecture of the microstructures.
[0026] In some embodiments, barrier ribs portions in PDPs typically
have heights of about 120 .mu.m to 140 .mu.m and widths of about 20
.mu.m to 75 .mu.m. It may be preferred that the pitch (number per
unit length) of the barrier ribs matches the pitch of the
electrodes. In other embodiments, the pitch of the barrier ribs in
the mold can be larger or smaller than the pitch of the electrodes,
and the mold can be stretched to align the ribs with the
electrodes, e.g., as described in U.S. Pat. No. 6,247,986 B1 to
Chiu et al., entitled METHOD FOR PRECISE MOLDING AND ALIGNMENT OF
STRUCTURES ON A SUBSTRATE USING A STRETCHABLE MOLD.
[0027] When using the techniques described herein to form
microstructures on a substrate (such as barrier ribs for a PDP),
the curable material from which the microstructures are formed can
be a slurry or paste, e.g., as described in U.S. Pat. No. 6,352,763
B1 to Dillon et al., entitled CURABLE SLURRY FOR FORMING CERAMIC
MICROSTRUCTURES ON A SUBSTRATE USING A MOLD. In an illustrative
aspect, the techniques as described herein may include using a
slurry that contains a ceramic powder, a curable organic binder,
and a diluent, e.g., the slurries described in U.S. Pat. No.
6,352,763 B1. When the binder is in its initial uncured state, the
slurry can be shaped and aligned on a substrate using a mold. After
curing the binder, the slurry is in at least a semi-rigid state
that can retain the shape in which it was molded. This cured, rigid
state is referred to as the green state, just as shaped ceramic
materials are called "green" before they are sintered. When the
slurry is cured, the mold can be removed from the green state
microstructures. The green state material can subsequently be
debinded and/or fired. Debinding, or burn out, occurs when the
green state material is heated to a temperature at which the binder
can diffuse to a surface of the material and volatilize. Debinding
is usually followed by increasing the temperature to a
predetermined firing temperature to sinter or fuse the particles of
the ceramic powder. After firing, the material can be referred to
as fired material. Fired microstructures are referred to herein as
ceramic micro structures.
[0028] Generally, the techniques described herein typically use a
mold to form the microstructures. The mold may be a flexible
polymer sheet having a smooth surface and an opposing
microstructured surface. The mold can be made by compression
molding of a thermoplastic material using a master tool that has a
microstructured pattern. In some embodiments, the mold can also be
made of a curable material that is cast and cured onto a thin,
flexible polymer film. The microstructured mold can be formed, for
example, using techniques disclosed in U.S. Pat. No. 5,175,030 to
Lu et al., entitled MICROSTRUCTURE-BEARING COMPOSITE PLASTIC
ARTICLES AND METHOD OF MAKING; U.S. Pat. No. 5,183,597 to Lu,
entitled METHOD OF MOLDING MICROSTRUCTURE BEARING COMPOSITE PLASTIC
ARTICLES; and U.S. Pat. No. 7,033,534 to Chiu et al., entitled
METHOD FOR FORMING MICROSTRUCTURES ON A SUBSTRATE USING A MOLD.
[0029] FIGS. 2a-e are schematic diagrams of one embodiment of a
method of forming microstructures on a substrate. In FIG. 2a, an
apparatus 100 for molding microstructures on a substrate is
illustrated. The apparatus 100 includes a substrate 110, a flexible
mold 130, and a laminating roller 140. The substrate 110 can be any
substrate described herein. The flexible mold 130 includes a
flexible backing 132 and a microstructured surface 134 on a major
surface of the flexible backing 132. The microstructured surface
134 includes rib forming regions 136 and land forming regions 138.
The flexible mold 130 in this embodiment is configured and arrayed
to form barrier regions (e.g., barrier ribs 124 of FIG. 2e) on
substrate 110.
[0030] Generally, a roller 140 or other pressure application device
can be provided to provide pressure to the mold 130 and a curable
material (e.g., curable material 120 of FIG. 2b) to drive a portion
of the curable material into rib forming regions 136 within the
microstructured surface 134 of the mold 130.
[0031] As shown in FIG. 2b, a curable material 120 is disposed on a
major surface 112 of substrate 110. Typically, the curable material
120 is coated on the substrate 110 using a coating technique that
can produce substantially uniform coatings, e.g., knife coating,
screen printing, extrusion coating, and reverse gravure coating.
The curable material 120 may include any suitable material or
materials as described herein.
[0032] The curable material 120 can be coated on one or more
regions of the substrate 110. In some embodiments, the curable
material 120 can be disposed on substantially the entire major
surface 112 of substrate 110. In some embodiments, the curable
material 120 may be disposed on region 116 of the substrate. Edge
portions 114 of major surface 112 can be left substantially free
from curable material 120 to provide areas for handling the
substrate or, particularly in the case of PDP and other display
technologies, areas free of curable material where sealing to the
front panel is performed and electrical connections can be made
with electrodes patterned on the substrate (not shown).
[0033] Generally, the thickness of the curable material 120 varies
by no more than 10%. It may be preferred that the thickness of the
curable material 120 varies by no more than 5%. It may be more
preferred that the thickness of curable material 120 varies by no
more than 2%. In one embodiment, the curable material 120 has an
average thickness of about 75 .mu.m. In another embodiment, the
average thickness of curable material 120 may be about 50
.mu.m.
[0034] It may be preferred that the area of the substrate 110 upon
which a lattice pattern is desired (e.g., region 116) has been
predetermined precisely beforehand, and the curable material 120 is
disposed only upon the area. The area of the substrate 110 having
no curable material 120 disposed thereon (e.g., edge portions 114)
can be used for handling during processing, and for electrical
connections in the case that the assembly is to be used in a
PDP.
[0035] In FIGS. 2b-c, the mold 130 contacts the curable material
120 beginning at a first end 118 of the substrate 110 as pressure
is applied to the mold 130 along direction 150. The roller 140 may
be used to apply pressure to the mold 130 such that the mold 130
contacts the curable material 120 beginning at the first end 118 of
the substrate 110. The mold 130 may be made to contact the curable
material 120 at any suitable contact speed in direction 150. It may
be preferred that the mold 130 contact curable material 120 at a
substantially uniform contact speed. Further, any suitable contact
pressure may be applied to mold 130 such that it contacts curable
material. It may be preferred that a substantially uniform contract
pressure is applied to the mold 130. The curable material 120 is
deformed such that the rib forming regions 136 of the
microstructured surface 134 of the flexible mold 130 become filled.
It may be preferred that the contact speed and contact pressure are
chosen such that the curable material 120 is not entirely squeezed
out from under the microstructured surface 134 of the flexible mold
130, thus leaving land regions in the curable material 120
corresponding to land forming regions 138 (e.g., land regions 126
of FIG. 2e).
[0036] As the mold 130 contacts the curable material 120, the
curable material is formed into a lattice pattern (e.g., lattice
pattern 20 of FIG. 1). For example, FIG. 2d illustrates one
embodiment of a microstructured assembly 160. The microstructured
assembly 160 includes the substrate 110, the flexible mold 130, and
the curable material 120. The microstructured surface 134 of mold
130 is configured to impart a lattice pattern into the curable
material 120. In some embodiments, the lattice pattern includes a
first set of ribs (e.g., first set of ribs 22 of FIG. 1) aligned in
a first direction (e.g., direction 16 of FIG. 1) and a second set
of ribs (e.g., second set of ribs 24 of FIG. 1) aligned in a second
direction (e.g., second direction 18 of FIG. 1). Further, the
lattice pattern can include land regions 126. As illustrated in
FIG. 2d, ribs 124 are included in the second set of ribs, whereas
the first set of ribs are not shown.
[0037] In FIG. 2d, the curable material 120 is cured to form ribs
124 on major surface 112 of substrate 110. Curing of the material
120 can take place in a variety of ways depending on the binder
used. For example, the material can be cured using one or more
curing devices providing visible light, ultraviolet light, e-beam
radiation, or other forms of radiation, or by heat curing or by
cooling to solidification from a melted state. For radiation
curing, radiation can be propagated through the substrate 110,
through the mold 130, or through the substrate 110 and the mold
130. Preferably, the cure system chosen facilitates adhesion of the
cured material 120 to the substrate 110.
[0038] After curing the material 120, the mold 130 can be removed
(e.g., by winding the mold onto a receiving element, e.g., a
roller). A flexible mold can aid in mold removal because the mold
can be peeled back so that the demolding force can be focused on a
smaller surface area. It may be preferred that a mold release
material is included either as a coating on the patterned surface
of the mold or in the material that is hardened to form the lattice
pattern itself A mold release material becomes more important as
higher aspect ratio structures are formed. Higher aspect ratio
structures make demolding more difficult and can lead to damage to
the microstructures.
[0039] After the mold 130 is removed, what remains is the substrate
110 having a plurality of hardened microstructures adhered thereon.
Depending on the application, this can be the finished product. In
other applications, such as substrates that will have a plurality
of microstructures, the hardened material contains a binder that is
preferably removed by debinding at elevated temperatures. After
debinding, or burning out of the binder, firing of the green state
ceramic microstructures is performed to fuse the glass particles or
sinter the ceramic particles in the material of the
microstructures. This increases the strength and rigidity of the
microstructures. Shrinkage can also occur during firing as the
microstructure densifies. Fired microstructures maintain their
positions and their pitch according to the substrate pattern.
[0040] For PDP display applications, phosphor material is applied
between the barrier regions of the microstructures. The substrate
then can be installed into a display assembly. This involves
aligning a front substrate having sustain electrodes with the back
substrate having address electrodes, microstructures, and phosphor
such that the sustain electrodes are perpendicular with the address
electrodes. The areas through which the opposing electrodes cross
define the pixels of the display. The space between the substrates
is then evacuated and filled with an inert gas as the substrates
are bonded together and sealed at their edges.
[0041] It will be recognized that other articles can also be formed
using a substrate with the molded microstructures. For example, the
molded microstructures can be used to form capillary channels for
applications such as electrophoresis plates. In addition, the
molded microstructures could be used for plasma displays or other
applications that produce light.
[0042] As the mold contacts the curable material, air may become
trapped between the microstructured surface of the mold and the
curable material. This trapped air may in turn form air bubbles
within the microstructures formed in the curable material. It may
be preferred that any trapped air be removed from between the mold
and the curable material.
[0043] In the present application, "small bubbles" refers to air
bubbles that are less that half the rib height (or other
microstructural feature size) in size. The presence of such small
bubbles is not preferred, but may not disrupt the continuity of the
ribs or other microstructural features, and hence, may not
significantly degrade functionality. "Large bubbles" refers to air
bubbles which are about half the rib height or larger in size.
Large bubbles can disrupt the continuity of the ribs or other
microstructural features and significantly degrade functionality.
In the present application, the word "defects" refers to damaged
ribs or structures, such as broken ribs or ribs with missing
sections, as well as to large bubbles.
[0044] One way in which the trapped air can be removed is through
grooves that, in some embodiments, form the microstructured surface
of the mold. For example, FIG. 3 is a schematic diagram of a path
taken by an air bubble as it is removed during the application of a
flexible mold having a microstructured surface to a curable
material. In FIG. 3, the flexible mold (not shown) is applied in a
first direction 212. The lattice pattern 220 that is formed in the
curable material 216 includes a first set of ribs 222 aligned in
the first direction 212. Lattice pattern 220 further includes a
second set of ribs 224 aligned in a second direction 214. A first
air bubble 230 is shown schematically within one rib 226 of the
second set of ribs 224. For the first air bubble 230 to escape
during application of the flexible mold, it must migrate into an
area between a rib of the first set of ribs 222 and the mold, so
that it can be squeezed out of the curable material 216 along the
direction of application of the flexible mold, i.e., the first
direction 212. A bubble that has so migrated is shown schematically
as second air bubble 232.
[0045] One technique that may aid in the removal of trapped air may
include controlling certain dimensions of the rib forming regions
(i.e., grooves) of a microstructured surface of a mold.
[0046] FIGS. 4a-c are schematic diagrams of a flexible mold 300.
The flexible mold 300 is applied to a curable material in direction
310 as further described herein. The flexible mold 300, which
includes a negative image of the lattice pattern to be formed in
the curable material, will have rib forming regions where the rib
assembly is to have ribs. The mold 300 includes a first set of rib
forming regions 320 and a second set of rib forming regions 330. It
is to be understood that the rib forming regions 320 and 330 of the
mold 300 will form ribs in a curable material that have
substantially the same shape and dimensions as the corresponding
rib forming regions. Note that the first set of rib forming regions
320 are aligned in the first direction 310 and the second set of
rib forming regions 330 are aligned in the second direction 312. In
some embodiments, the first set of rib forming regions 320 need not
be identical in shape and size to the second set of rib forming
regions 330.
[0047] As shown in FIG. 4b, each rib forming region of the first
set of rib forming regions 320 includes an opening width 322 and a
bottom width 324. Further, as shown in FIG. 4c, each rib forming
region of the second set of rib forming regions 330 includes an
opening width of 332 and a bottom width of 334. In other
embodiments, the rib forming regions may have opening widths equal
in size to the bottom widths. Alternatively, the opening width may
be greater than the bottom width for one or more rib forming
regions of one of the first set of rib forming regions 320 and
second set of rib forming regions 330 or both sets of rib forming
regions. Further, the side walls of the rib forming regions may be
any suitable shape, e.g., curved, straight, parabolic. The side
walls of each rib forming region may also include textured or
patterned surfaces.
[0048] Each rib forming region of the first set of rib forming
regions 320 has a depth 328. Similarly, each rib forming region of
the second set of rib forming regions 330 has a depth 338. The
depths of each rib forming region may be the same for the first set
of rib forming regions 320 or the second set of rib forming regions
330. Alternatively, the depth of each rib forming region of the
first set of rib forming regions 320 or the second set of rib
forming regions 330 may vary.
[0049] Further, each rib forming region of the first set of rib
forming regions 320 may have the same shape and dimensions as the
rest of the rib forming regions in the first set; alternatively,
the rib forming regions of the first set of rib forming regions 320
may have different shapes and dimensions. In other embodiments, the
second set of rib forming regions 330 may include rib forming
regions that have the same shapes and dimensions, or the rib
forming regions may have varying shapes and dimensions.
[0050] Each rib forming region of the first set of rib forming
regions 320 includes an average width that is one-half the sum of
the opening width 322 and the bottom width 324. Similarly, the
average width of each rib forming region of the second set of rib
forming regions 330 is one-half the sum of the opening width 332
and the bottom width 334. The average width of each rib forming
region of the first set of rib forming regions 320 and the average
width of each rib forming region of the second set of rib forming
regions 320 need not be equal.
[0051] The first set of rib forming regions 320 includes a pitch
326, and the second set of rib forming regions 330 includes a pitch
336. The pitch 326 of the first set of rib forming regions 320 and
the pitch 336 of the second set of rib forming regions 330 may be
equal. In some embodiments, the pitch 326 of the first set of rib
forming regions 320 may be greater or less than the pitch 336 of
the second set of rib forming regions 330.
[0052] Several factors may influence the removal of air bubbles
from the curable material. For example, the viscosity of the
curable material, the pitch 326 of the first set of rib forming
regions 320, and the pitch 336 of the second set of rib forming
regions 330 may affect the removal of air bubbles. Other parameters
may also have an effect. For example, the ratio of the average
width of each rib forming region of the second set of rib forming
regions 330 and the average width of each rib forming region of the
first set of rib forming regions 320, the shape of the rib forming
regions, and the coated thickness of the curable material may
influence bubble formation and removal. Another such parameter is
the application (roller) loading or pressure as the flexible mold
is being applied to the curable material and the speed or rate of
the application (roller travel).
[0053] To aid in preventing bubble formation, it may be preferred
that the viscosity of the curable material is less than 12,000 cps.
Further, it may be preferred that the pitch of the first set of rib
forming regions 320 is less than 500 .mu.m. It may be more
preferred that the pitch of the first set of rib forming regions is
less than 300 .mu.m.
[0054] Further, it may be preferred that the ratio of the average
width of each rib forming region of the second set of rib forming
regions 330 and the average width of each rib forming region of the
first set of rib forming regions is at least 1.5. Without wishing
to be bound by any theory, it is believed that widening each rib
forming region of the second set of rib forming regions 330 with
respect to the width of each rib forming region of the first set of
rib forming regions 320 alters the pressure drops in the respective
channels during application of the flexible mold in such a way as
to enable ever-smaller bubbles to escape by the route shown
schematically in FIG. 3. One skilled in the art will appreciate
that increasing the value of the ratio of the average width of each
rib forming region of the second set of rib forming regions and the
average width of each rib forming region of the first set of rib
forming regions beyond 1.5 will lead progressively to the
elimination of smaller and smaller air bubbles, if desired.
[0055] Also, the length of the path an air bubble must traverse in
order to escape by the route shown schematically in FIG. 3 may
further influence the removal of air bubbles from the curable
material. For example, the edge-to-edge bottom distance of the
first set of rib forming regions 320 may in some instances be less
than 150 .mu.m or more than 300 .mu.m. One skilled in the art will
appreciate that if this distance is less than 150 .mu.m, the value
of the ratio of the average width of each rib forming region of the
second set of rib forming regions 330 and the average width of each
rib forming region of the first set of rib forming regions 320
effective for bubble removal may be lower than 1.5. Conversely, if
the distance is greater than 300 .mu.m, the value of this ratio
necessary for effective bubble removal may be greater than 1.5.
[0056] Another factor that may influence bubble removal is the
quantity of curable material disposed on the substrate prior to the
flexible mold contacting the curable material. As further described
herein, the curable material is disposed on the substrate in an
area of the substrate upon which the lattice rib pattern is
intended to be formed (e.g., region 116 of substrate 110 as
illustrated in FIG. 2b). Conditions may be selected such that the
amount of curable material squeezed out from under the
microstructured surface of the flexible mold is substantially equal
to the amount of curable material squeezed up into the rib forming
regions of the microstructured surface. The first set of rib
forming regions, which correspond to the first set of ribs aligned
in the first direction, provide an air channel by which air bubbles
can escape.
[0057] If, however, the amount of curable material squeezed out
from under the microstructured surface of the flexible mold is
substantially in excess of the amount of curable material squeezed
up into the rib forming regions, a bank of curable material may be
formed ahead of the advance of the flexible mold. This results in a
"paste overflow" condition. When the bank is created, one or more
rib forming regions of the second set of rib forming regions (e.g.,
second set of rib forming regions 330 of FIG. 4a) become filled out
of sequence. The first set of rib forming regions provides an air
channel by which air bubbles can escape (see, e.g., FIG. 3).
However, when one or more rib forming regions of the second set of
rib forming regions become filled out of sequence, this air channel
provided by the first set of rib forming regions becomes blocked;
therefore, some of the air bubbles may not completely escape.
[0058] Not only may the amount of curable material disposed on the
substrate affect air bubble removal, the viscosity of the curable
material along with the pressure or loading applied by the roller,
and the speed at which the roller travels may also affect air
bubble removal. For example, too low a viscosity for the curable
material can also lead to paste overflow.
EXAMPLES
Example 1
[0059] A metal mold was prepared to the desired dimensions of the
lattice pattern assembly to be made. The metal mold includes a
microstructured surface having a first set of rib forming regions
aligned in a first direction and a second set of rib forming
regions aligned in a second direction substantially orthogonal to
the first direction. The first set of rib forming regions had a
pitch of 300 .mu.m. Each rib forming region of the first set of rib
forming regions had a height of 208 .mu.m, an opening width of 55
.mu.m, and a bottom width of 115 .mu.m. The dimension of these rib
forming regions would form a rib having a taper angle of 82
degrees. The taper angle is the included angle at the base of a
rib. A rib forming region with equal opening and bottom widths
would form a rib having a taper angle of 90 degrees. The second set
of rib forming regions had a pitch of 500 .mu.m. Each rib forming
region had a height of 208 .mu.m, an opening width of 37 .mu.m, and
a bottom width of 160 .mu.m, which would result in a rib taper
angle of 75 degrees.
[0060] A mixture of 99% by wt. of an aliphatic urethane acrylate
oligomer (Photomer 6010.TM., manufactured by Henkel Co.) and 1% by
wt. 2-hydroxyl-2-methyl-1-phenyl-propane-1-one (Darocure 1173.TM.,
manufactured by Ciba-Gigy) as a photoinitiator was prepared. An
amount slightly in excess of that needed to completely fill the
microstructured surface of the mold was placed between a PET film
and the metal mold. The mixture was cured by exposure to radiation
of wavelength 300-400 nm for 30 sec. The thus-cured urethane
acrylate polymer adhered strongly to the PET film and was released
together with the PET film from the metal mold to obtain a flexible
and transparent plastic mold. The rib forming regions in the
flexible mold had the same shape and the same dimensions as the rib
forming regions in the metal mold.
[0061] A ceramic paste was prepared to serve in the molding method
as the curable material. 21.0 g of dimethacrylate of bisphenol A
diglycidyl ether (Kyoeisha Chemical Co., Ltd.), 9.0 g of
triethylene glycol dimethacrylate (Wako Pure Chemical Industries,
Ltd.), 30.0 g of 1,3-butandiol (Wako Pure Chemical Industries,
Ltd.) as a dilutant, 0.3 g of
bis(2,4,6-trimethylbenzoyl)-phenylphospheneoxide (Irgacure 819,
made by Ciba-Geigy) as an initiator, 3.0 g of phosphated
polyoxyalkyl polyol (POCA) as a surfactant, and 180.0 g of a
mixture of glass frit and ceramic particles (RFW-030, made by Asahi
Glass Co) were mixed to obtain the photocurable ceramic paste. The
paste viscosity was 6000 cps (as measured at 22.degree. C. and 20
rpm with spindle No. 5 on a type B viscometer).
[0062] The ceramic paste was coated onto a glass substrate to a
thickness of 200 .mu.m, and then the flexible mold was applied in a
first direction, with a roller, onto the paste. Afterwards, the
assembly was exposed to radiation of wavelength 400-500 nm for 30 s
to cure the paste. The flexible mold was peeled from the substrate
in the first direction. The substrate and cured ribs assembly was
then sintered at 550.degree. C. for 1 h to burn out the organic
part of the ribs. After the sintering, the ribs were evaluated
using an optical microscope. Either damage to a rib or a bubble in
a rib that was so large as to significantly disrupt the continuity
of the rib were regarded as defects. Sometimes, very small air
bubbles are observed on the very tops of the lateral ribs. These
small air bubbles are approximately an order of magnitude smaller
than the heights of the ribs, so they do not significantly disrupt
the continuity of the rib. No defects were observed in this
specimen. Small air bubbles were observed in this specimen.
[0063] Defect level in this and other Examples was defined as a
ratio of the number of defects detected to the number of rib
segments of the set of second direction ribs in the visual field
(7.5 mm in diameter) of the microscope. This measurement was done
in seven randomly-selected areas on the specimen, and the average
of the seven results is reported. The defect level of Example 1 was
0.0%.
Examples 2 and 3
[0064] The flexible molds were made as described in Example 1. The
viscosity of the paste was varied by varying the solids content
(glass frit and ceramic particles). Solids content was 90.0 g in
Example 2 and 145.0 g in Example 3. All other components were
identical in type and loading level as those in Example 1. The
paste viscosities were 1800 cps for Example 2 and 4800 cps for
Example 3.
[0065] Lattice pattern rib assemblies were made in the same way as
in Example 1. The defect level was measured by microscopy. The
defect levels of both Examples 2 and 3 were 0.0%. Small bubbles
were observed in these specimens.
Comparative Examples 1 and 2
[0066] The flexible molds were made as described in Example 1. The
viscosity of the paste was varied by varying the solids content
(glass frit and ceramic particles). Solids content was 220.0 g in
Comparative Example 1 and 270.0 g in Comparative Example 2. All
other components were identical in type and loading level as in
Example 1. The paste viscosities were 12,600 cps for Comparative
Example 1 and 27,300 cps for Comparative Example 2.
[0067] Lattice pattern rib assemblies were made in the same way as
in Example 1. The defect level was measured by microscopy. The
defect levels were 0.1% for Comparative Example 1 and 3.3% for
Comparative Example 2. Small bubbles were also observed in these
specimens.
Comparative Example 3
[0068] A flexible mold and a ceramic paste were made as described
in Example 1, with the exception that the first direction and
second direction of the mold were reversed. Thus, the pitch in the
first direction was 500 .mu.m. The paste viscosity was 6000 cps.
Lattice pattern rib assemblies were made in the same way as in
Example 1.
[0069] The defect level was measured by microscopy. Many defects
were observed in this specimen. All cross members included defects,
which means that the defect level is 100% in Comparative Example 3.
Small bubbles were also observed in this specimen.
Example 4
[0070] A flexible plastic mold having lattice pattern
microstructured surface was prepared using the same materials as in
Example 1.
[0071] The microstructured surface in the mold corresponded to ribs
having the following dimensions. Ribs of the first set of ribs had
a pitch of 300 .mu.m, a height of 200 .mu.m, an opening width of 50
.mu.m, and a bottom width of 100 .mu.m. The ribs of the second set
of ribs had a pitch of 500 .mu.m, a height of 200 .mu.m, an opening
width of 150 .mu.m, and a bottom width of 220 .mu.m.
[0072] The average width of each rib of the first set of ribs was
thus (50+100)/2=75 and, the average width of each rib of the second
set of ribs was thus (150+220)/2=185. The ratio of the average
width of each rib of the second set of ribs and the average width
of each rib of the first set of ribs was thus 185/75, or about
2.5.
[0073] A ceramic paste was prepared to serve in the molding method
as the curable material. 21.0 g of dimethacrylate of bisphenol A
diglycidyl ether (Kyoeisha Chemical Co., Ltd.), 9.0 g of
triethylene glycol dimethacrylate (Wako Pure Chemical Industries,
Ltd.), 30.0 g of 1,3-butandiol (Wako Pure Chemical Industries,
Ltd.) as a dilutant, 0.2 g of
bis(2,4,6-trimethylbenzoyl)-phenylphospheneoxide (Irgacure 819,
made by Ciba-Geigy) as an initiator, 1.5 g of phosphateed
polyoxyalkyl polyol (POCA) and 1.5 g of sodium
dodecylbenzenesulfonate (NeoPelex #25, made by Kao Co.) as
surfactants, and 270.0 g of a mixture of glass frit and ceramic
particles (RFW-030, made by Asahi Glass Co) were mixed to obtain
the photocurable ceramic paste. The paste viscosity was 7300 cps
(as measured at 22.degree. C. and 20 rpm with spindle No. 5 on a
type B viscometer).
[0074] The ceramic paste was coated on a glass substrate to a
thickness of 130 .mu.m by a blade coater, and then the flexible
mold was applied along the first direction onto the paste using a
rubber roller.
[0075] Afterwards, the assembly was exposed to radiation of
wavelength 400-500 nm for 30 s to cure the paste. The flexible mold
was peeled from the substrate in the first direction.
[0076] The sizes of air bubbles near the tops of the ribs of the
second set of ribs were measured at 18 points by microscopy. The
average air bubble size is summarized in Table 1. No defects or
small air bubbles were observed in Example 4.
Examples 5 and 6
[0077] Flexible plastic molds having different rib forming region
shapes from Example 4 were prepared.
[0078] The rib shapes corresponding to those rib forming region
shapes are described as follows.
Example 5
[0079] Ribs of the first set of ribs had a pitch of 300 .mu.m, a
height of 200 .mu.m, an opening width of 50 .mu.m, and a bottom
width of 100 .mu.m. The ribs of the second set of ribs had a pitch
of 500 .mu.m, a height of 200 .mu.m, an opening width of 125 .mu.m,
and a bottom width of 190 .mu.m.
[0080] The average width of each rib of the first set of ribs was
thus (50+100)/2=75 and, the average width of each rib of the second
set of ribs was thus (125+190)/2=157.5. The ratio of the average
width of each rib of the second set of ribs and the average width
of each rib of the first set of ribs was thus 157.5/75=2.1.
Example 6
[0081] Ribs of the first set of ribs had a pitch of 300 .mu.m, a
height of 200 .mu.m, an opening width of 50 .mu.m, and a bottom
width of 100 .mu.m. The ribs of the second set of ribs had a pitch
of 500 .mu.m, a height of 200 .mu.m, an opening width of 100 .mu.m,
and a bottom width of 170 .mu.m.
[0082] The average width of each rib of the first set of ribs was
thus (50+100)/2=75 and, the average width of each rib of the second
set of ribs was thus (100+170)/2=135 The ratio of the average width
of each rib of the second set of ribs and the average width of each
rib of the first set of ribs is thus 135/75=1.8.
[0083] The lattice pattern ribs were formed by using the mold as
described in Example 4. The sizes of air bubble near the tops of
the ribs of the second set of ribs were measured at 18 points by
microscopy. The average air bubble size is summarized in Table 1.
No defects or small air bubbles were observed in Example 5 or
6.
Examples 7 and 8
[0084] Flexible plastic molds that have different rib forming
region shapes from Example 4 were prepared.
[0085] The rib shapes corresponding to those rib forming region
shapes are described as follows.
Example 7
[0086] Ribs of the first set of ribs had a pitch of 300 .mu.m, a
height of 200 .mu.m, an opening width of 50 .mu.m, and a bottom
width of 100 .mu.m. The ribs of the second set of ribs had a pitch
of 500 .mu.m, a height of 200 .mu.m, an opening width of 75 .mu.m,
and a bottom width of 140 .mu.m.
[0087] The average width of each rib of the first set of ribs was
thus (50+100)/2=75 and, the average width of each rib of the second
set of ribs was thus (75+140)/2=107.5. The ratio of the average
width of each rib of the second set of ribs and the average width
of each rib of the first set of ribs was thus 107.5/75=1.4.
Example 8
[0088] Ribs of the first set of ribs had a pitch of 300 .mu.m, a
height of 200 .mu.m, an opening width of 60 .mu.m, and a bottom
width of 120 .mu.m. The ribs of the second set of ribs had a pitch
of 500 .mu.m, a height of 200 .mu.m, an opening width of 60 .mu.m,
and a bottom width of 110 .mu.m.
[0089] The average width of each rib of the first set of ribs is
thus (60+120)/2=90 and, the average width of each rib of the second
set of ribs is thus (60+110)/2=85. The ratio of the average width
of each rib of the second set of ribs and the average width of each
rib of the first set of ribs is thus 85/90=0.94.
[0090] The lattice pattern ribs were formed by using the mold as
described in Example 4. The sizes of air bubbles near the tops of
the ribs of the second set of ribs were measured at 18 points by
microscopy. The average air bubble size is summarized in Table 1.
The average sizes of air bubbles were 18 .mu.m and 25 .mu.m in
examples 7 and 8, respectively. No defects were observed in these
specimens, however.
TABLE-US-00001 TABLE 1 Ratio Air bubble size Example 4 2.5 0 micron
Example 5 2.1 0 micron Example 6 1.8 0 micron Example 7 1.4 18
micron Example 8 0.9 25 micron
Example 9
[0091] A metal mold was prepared to the desired dimensions of the
lattice pattern assembly to be made. The metal mold includes a
microstructured surface having a first set of rib forming regions
aligned in a first direction and a second set of rib forming
regions aligned in a second direction substantially orthogonal to
the first direction. The first set of rib forming regions had a
pitch of 300 .mu.m. Each rib forming region of the first set of rib
forming regions had a height of 200 .mu.m, an opening width of 60
.mu.m, and a bottom width of 120 .mu.m. The second set of rib
forming regions had a pitch of 500 .mu.m, a height of 200 .mu.m, an
opening width of 40 .mu.m, and a bottom width of 160 .mu.m,
resulting in a rib taper angle of 75 degrees.
[0092] A mixture of 99% by wt. of an aliphatic urethane acrylate
oligomer (Photomer 6010.TM., manufactured by Henkel Co.) and 1% by
wt. 2-hydroxyl-2-methyl-1-phenyl-propane-1-one (Darocure 1173.TM.,
manufactured by Ciba-Gigy) as a photoinitiator was prepared. An
amount slightly in excess of that needed to completely fill the
microstructure of the mold was placed between a PET film and the
metal mold. The mixture was cured by exposure to radiation of
wavelength 300-400 nm for 30 sec. The thus-cured urethane acrylate
polymer adheres strongly to the PET film, and was released together
with the PET film from the metal mold to obtain a flexible and
transparent plastic mold. The grooves in the flexible mold had the
same shape and the same dimensions as the ribs in the metal
mold.
[0093] A ceramic paste was prepared to serve in the molding method
as the curable material. 21.0 g of dimethacrylate of bisphenol A
diglycidyl ether (Kyoeisha Chemical Co., Ltd.), 9.0 g of
triethylene glycol dimethacrylate (Wako Pure Chemical Industries,
Ltd.), 30.0 g of 1,3-butandiol (Wako Pure Chemical Industries,
Ltd.) as a dilutant, 0.2 g of
bis(2,4,6-trimethylbenzoyl)-phenylphospheneoxide (Irgacure 819,
made by Ciba-Geigy) as an initiator, 1.5 g of phosphateed
polyoxyalkyl polyol (POCA) and 1.5 g of sodium
dodecylbenzenesulfonate (NeoPelex #25, made by Kao Co.) as
surfactants, and 270.0 g of a mixture of glass frit and ceramic
particles (RFW-030, made by Asahi Glass Co) were mixed to obtain
the photocurable ceramic paste. The paste viscosity was 7300 cps
(as measured at 22.degree. C. and 20 rpm with spindle No. 5 on a
type B viscometer).
[0094] The ceramic paste was coated on a glass substrate to a
thickness of 110 .mu.m by a blade coater. The coating area was a
950.times.540 mm rectangle that corresponded to the lattice pattern
area of the mold. Then the flexible mold was applied along the
first direction onto the 110 micron thick layer of paste by using a
30 kg, 200 mm diameter roller at a rate of 42 mm/s. Since no
additional loading was given to the mold, the total loading to the
mold is 30 kg/950 mm, or about 0.032 kg/mm. Afterwards, the
assembly was exposed to radiation of wavelength 400-500 nm for 30 s
to cure the paste. The flexible mold was peeled from the substrate
in the first direction.
[0095] The amount of paste overflow resulting from the application
step was obtained by measuring the difference between the paste
coating area before the application of the flexible mold and the
paste coating area after the application of the flexible mold. The
specimen of Example 9 showed no difference in paste coating area
before and after the application of the flexible mold, which
indicates that the conditions of Example 9.
[0096] After the removal of the mold, the assembly of substrate and
lattice pattern ribs was sintered at 550.degree. C. for 1 h to burn
out the organic part of the ribs.
[0097] After the sintering, rib defects were measured by optical
microscopy. No defects were observed in the entire area
(950.times.540 mm) of the specimen of Example 9. Small air bubbles
were observed in this specimen.
Examples 10 and 11
[0098] The flexible plastic molds and photocurable ceramic paste
were made as described in Example 9.
[0099] The ceramic paste was coated on a glass substrate to a
thickness of 110 .mu.m by a blade coater. The coating area was a
950.times.540 mm rectangle that corresponded to the lattice pattern
area of the mold. Then the flexible mold was applied along the
first direction onto the 110 micron thick layer of paste. For
Example 10, a 30 kg, 200 mm diameter roller was used at a rate of
20 mm/s. For Example 11, a 100 kg, 200 mm diameter roller was used
at a rate of 42 mm/s. Since no additional loading was given to the
mold, the total loading to the mold is 30 kg/950 mm, or about 0.032
kg/mm for Example 10, and is 100 kg/950 mm, or about 0.105 kg/mm
for Example 11. Afterwards, the assembly was exposed to radiation
of wavelength 400-500 nm for 30 s to cure the paste. The flexible
mold was peeled from the substrate in the first direction.
[0100] The amount of paste overflow resulting from the application
step was obtained by measuring the difference between the paste
coating area before the application of the flexible mold and the
paste coating area after the application of the flexible mold. The
specimens of Examples 10 and 11 showed no difference in paste
coating area before and after the application of the flexible mold,
which indicates that the conditions of Examples 10 and 11 did not
lead to "paste overflow" conditions.
[0101] After the removal of the mold, the assembly of substrate and
lattice pattern ribs was sintered at 550.degree. C. for 1 h to burn
out the organic part of the ribs.
[0102] After the sintering, rib defects were measured by optical
microscopy. No defects were observed in the entire area
(950.times.540 mm) of the specimens of Examples 10 and 11. Small
air bubbles were observed in these specimens.
Comparative Example 4
[0103] The flexible plastic molds were made as described in Example
9. The paste viscosity was lowered by decreasing the content of the
RFW-030 in the paste. 180.0 g of RFW-030 was used instead of the
270.0 g used in Example 9. The amounts of all other ingredients of
the paste were identical. The viscosity was 3000 cps.
[0104] The ceramic paste was coated on a glass substrate to a
thickness of 110 .mu.m by a blade coater. The coating area was a
950.times.540 mm rectangle that corresponded to the lattice pattern
area of the mold. Then the flexible mold was applied along the
first direction onto the 110 micron thick layer of paste by using a
100 kg, 200 mm diameter roller at a rate of 20 mm/s. Since no
additional loading was given to the mold, the total loading to the
mold is 100 kg/950 mm, or about 0.105 kg/mm. Afterwards, the
assembly was exposed to radiation of wavelength 400-500 nm for 30 s
to cure the paste. The flexible mold was peeled from the substrate
in the first direction.
[0105] The amount of paste overflow resulting from the application
step was obtained by measuring the difference between the paste
coating area before the application of the flexible mold and the
paste coating area after the application of the flexible mold. The
specimen of Comparative Example 4 showed a difference in paste
coating area before and after the application of the flexible mold
of more than 50 mm in the first direction, which indicates that the
conditions of Comparative Example 4 can be said to be "paste
overflow" conditions.
[0106] After the removal of the mold, the assembly of substrate and
lattice pattern ribs was sintered at 550.degree. C. for 1 h to burn
out the organic part of the ribs.
[0107] After the sintering, rib defects were measured by optical
microscopy. More than 100 defects were observed in the entire area
(950.times.540 mm) of the specimen Comparative Example 4. Small air
bubbles were also observed in this specimen.
[0108] All references and publications cited herein are expressly
incorporated herein by reference in their entirety into this
disclosure. Illustrative embodiments of this invention are
discussed and reference has been made to possible variations within
the scope of this invention. These and other variations and
modifications in the invention will be apparent to those skilled in
the art without departing from the scope of the invention, and it
should be understood that this invention is not limited to the
illustrative embodiments set forth herein. Accordingly, the
invention is to be limited only by the claims provided below.
* * * * *