U.S. patent application number 10/767631 was filed with the patent office on 2004-09-23 for microporous separators.
Invention is credited to Carlson, Steven Allen.
Application Number | 20040185335 10/767631 |
Document ID | / |
Family ID | 22484808 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040185335 |
Kind Code |
A1 |
Carlson, Steven Allen |
September 23, 2004 |
Microporous separators
Abstract
Provided are methods of preparing an article, such as an
electrochemical cell, in which a microporous layer is coated on a
temporary carrier substrate and a substrate, such as an electrode,
is then laminated or contacted to the microporous layer, after or
prior to removing the temporary carrier substrate from the
microporous layer. The microporous layer comprises one or more
microporous xerogel layers comprising a xerogel material, such as a
zirconium oxide xerogel material. Also provided are articles, such
as electrochemical cells and separators, prepared by such
methods.
Inventors: |
Carlson, Steven Allen;
(Cambridge, MA) |
Correspondence
Address: |
Optodot Corporation
Attn: Intellectual Property Department
Suite 305
214 Lincoln Street
Allston
MA
02134
US
|
Family ID: |
22484808 |
Appl. No.: |
10/767631 |
Filed: |
January 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10767631 |
Jan 29, 2004 |
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10325074 |
Dec 20, 2002 |
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10325074 |
Dec 20, 2002 |
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09590457 |
Jun 9, 2000 |
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6497780 |
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60139031 |
Jun 9, 1999 |
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Current U.S.
Class: |
429/145 |
Current CPC
Class: |
H01G 11/52 20130101;
H01G 11/82 20130101; H01M 4/0419 20130101; Y10S 428/914 20130101;
Y10T 428/2486 20150115; H01M 8/1004 20130101; H01M 4/0426 20130101;
Y10T 428/24997 20150401; B41M 5/5218 20130101; Y10T 428/24893
20150115; H01G 9/155 20130101; H01M 4/04 20130101; G02F 1/1525
20130101; Y10T 428/249969 20150401; B01D 69/10 20130101; H01M 50/46
20210101; B01D 67/0048 20130101; B01D 69/122 20130101; H01M 4/0416
20130101; H01M 4/0435 20130101; B32B 37/025 20130101; H01M 50/457
20210101; H01M 4/0402 20130101; H01M 4/0411 20130101; Y02E 60/13
20130101; Y10T 428/24942 20150115; Y02E 60/50 20130101; B01D
2325/02 20130101; B01D 71/024 20130101; H01M 50/449 20210101; H01M
4/0421 20130101; H01M 8/1213 20130101; H01M 50/491 20210101; H01M
4/0404 20130101; B32B 2305/026 20130101; B41M 5/508 20130101; B01D
69/12 20130101; Y02E 60/10 20130101; B41M 5/52 20130101; Y10T
428/249967 20150401; H01G 11/28 20130101; Y10T 428/29 20150115;
H01M 4/0414 20130101 |
Class at
Publication: |
429/145 |
International
Class: |
H01M 002/16 |
Claims
1. A separator comprising a microporous layer, wherein said
separator is prepared according to a method comprising the steps
of: (a) coating a microporous layer on a temporary carrier
substrate to form a microporous layer assembly, wherein said
microporous layer has a first surface in contact with said
temporary carrier substrate and has a second surface on the side
opposite from said temporary carrier substrate; (b) coating an
overlying layer on said second surface of said microporous layer,
wherein said overlying layer has a first surface in contact with
said second surface of said microporous layer and has a second
surface on the side opposite from said microporous layer; and (c)
removing said temporary carrier substrate from said first surface
of said microporous layer to form said separator; wherein said
microporous layer comprises one or more microporous xerogel layers
and wherein at least one of the one or more microporous xerogel
layers comprises a zirconium oxide xerogel material.
2. The separator of claim 1, wherein said microporous layer further
comprises an organic polymer binder.
3. The separator of claim 2, wherein said organic polymer binder is
a polyvinyl alcohol.
4. The separator of claim 2, wherein said microporous layer further
comprises a plasticizer component.
5. The separator of claim 1, wherein the thickness of said
separator is from 1 to 25 microns.
6. The separator of claim 1, wherein the thickness of said
separator is from 5 to 15 microns.
7. A separator for use in an electrochemical cell, wherein said
separator comprises a microporous xerogel layer, which xerogel
layer comprises zirconium oxide.
8. The separator of claim 7, wherein said microporous layer further
comprises an organic polymer binder.
9. The separator of claim 8, wherein said organic binder is
polyvinyl alcohol.
10. The separator of claim 8, wherein said microporous layer
further comprises a plasticizer component.
11. The separator of claim 7, wherein the thickness of said
separator is from 1 to 25 microns.
12. The separator of claim 7, wherein the thickness of said
separator is from 5 to 15 microns.
13. An electrochemical cell comprising a cathode, an anode and a
separator comprising a microporous layer interposed between said
cathode and said anode, wherein said separator is prepared
according to a method comprising the steps of: (a) coating a
microporous layer on a temporary carrier substrate to form a
microporous layer assembly, wherein said microporous layer has a
first surface in contact with said temporary carrier substrate and
has a second surface on the side opposite from said temporary
carrier substrate; (b) coating an overlying layer on said second
surface of said microporous layer, wherein said overlying layer has
a first surface in contact with said second surface of said
microporous layer and has a second surface on the side opposite
from said microporous layer; and (c) removing said temporary
carrier substrate from said first surface of said microporous layer
to form said separator; wherein said microporous layer comprises
one or more microporous xerogel layers and wherein at least one of
the one or more microporous xerogel layers comprises a zirconium
oxide xerogel material.
14. The cell of claim 13, wherein said microporous layer further
comprises an organic polymer binder.
15. The cell of claim 14, wherein said organic polymer binder is a
polyvinyl alcohol.
16. The cell of claim 14, wherein said microporous layer further
comprises a plasticizer component.
17. The cell of claim 13, wherein said cell is a secondary
electrochemical cell.
18. The cell of claim 13, wherein said cell is a primary
electrochemical cell.
19. An electrochemical cell comprising a cathode, an anode, and a
separator interposed between said cathode and said anode, wherein
said separator comprises a microporous xerogel layer, which xerogel
layer comprises zirconium oxide.
20. The cell of claim 19, wherein said microporous layer further
comprises an organic polymer binder.
21. The cell of claim 20, wherein said organic polymer binder is a
polyvinyl alcohol.
22. The cell of claim 20, wherein said microporous layer further
comprises a plasticizer component.
23. The cell of claim 19, wherein said cell is a secondary
electrochemical cell.
24. The cell of claim 19, wherein said cell is a primary
electrochemical cell.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/325,074, filed Dec. 20, 2002, which is a
division of U.S. patent application Ser. No. 09/590,457, filed Jun.
9, 2000, now U.S. Pat. No. 6,497,780, which claims priority to U.S.
Provisional Patent Application Ser. No. 60/139,031, filed Jun. 9,
1999, the contents of which related applications are incorporated
herein by reference in their entirety for all purposes.
TECHNICAL FIELD
[0002] The present invention relates generally to the field of
articles comprising a microporous layer, and to the fields of
electrochemical cells and of separators for use in electrochemical
cells. More particularly, this invention pertains to methods of
preparing an article comprising a microporous layer in which a
microporous layer is coated on a temporary carrier substrate and a
substrate is then laminated to the microporous layer, prior to
removing the temporary carrier substrate from the microporous
layer. The present invention also pertains to articles, such as
electrochemical cells, separators, capacitors, fuel cells, ink jet
printing media, and filtration media, prepared by such methods.
BACKGROUND
[0003] Throughout this application, various publications, patents,
and published patent applications are referred to by an identifying
citation. The disclosures of the publications, patents, and
published patent applications referenced in this application are
hereby incorporated by reference into the present disclosure to
more fully describe the state of the art to which this invention
pertains.
[0004] U.S. patent application Ser. No. 08/995,089 titled
"Separators for Electrochemical Cells," filed Dec. 19, 1997, to
Carlson et al. of the common assignee, now U.S. Pat. No. 6,153,337,
describes microporous layers as separators for use in
electrochemical cells in which microporous layers comprise a
microporous pseudo-boehmite layer prepared by coating and drying a
boehmite sol. The microporous pseudo-boehmite separators and
methods of preparing such separators are described for both free
standing separators and as a separator layer coated directly onto
an electrode or another layer of the cell.
[0005] When a microporous layer, such as a microporous separator
layer, is coated directly onto an electrode, such as onto the
cathode, the microporous separator coating may require a relatively
smooth, uniform surface on the electrode and also may require a
mechanically strong and flexible electrode layer. For example, for
a microporous pseudo-boehmite layer having a xerogel structure,
these specific electrode surface and layer properties may be
required to prevent excessive stresses and subsequent cracking of
the xerogel layer during drying of the pseudo-boehmite coating on
the electrode surface and also during fabrication and use of
electrochemical cells containing the pseudo-boehmite xerogel
layer.
[0006] Besides separator-coated electrodes and electrochemical
cells, a large variety of other articles comprising a microporous
layer may require a relatively smooth, uniform surface on a
substrate to which the microporous layer is to be applied. Also,
the substrate may need to be mechanically strong and flexible. For
example, for a microporous xerogel layer as used in ink jet
printing media, such as described, for example, in U.S. Pat. No.
5,463,178 to Suzuki et al., such smooth, uniform, and other
substrate properties may be useful in preventing excessive stresses
and subsequent cracking of the xerogel layer, particularly when its
thickness is above 20 microns, and also useful in providing
excellent image quality. Some of the desired substrates in ink jet
printing media, such as canvas, cloth, non-woven fiber substrates,
and some grades of paper, have very rough and non-uniform surfaces
and are difficult to coat with the microporous xerogel layers which
typically provide the premium ink jet image quality. One approach
to overcome the surface deficiencies of the substrate is to
pre-coat the substrate with a coating layer. This approach may
reduce the surface roughness and non-uniformities, but involves the
expense and complexity of an additional coating step, usually does
not fully eliminate the surface deficiencies, and may negatively
affect the ink jet imaging, such as by interfering with the
microporosity and transport of liquids between the xerogel layer
and the rough but porous substrate.
[0007] In another approach that may overcome the surface
deficiencies of the substrate, the ink jet ink-receptive layer may
be coated on a temporary carrier layer to form an ink jet ink
printing media for imaging on an ink jet printer, as, for example,
described in U.S. Pat. Nos. 5,795,425 and 5,837,375, both to Brault
et al. Then, as part of a two step imaging process, the ink jet
media is imaged on the ink jet printer followed by lamination of
the imaged ink jet ink-receptive layer to a desired substrate and
removal of the temporary carrier layer from the ink jet
ink-receptive layer. This approach has the disadvantage of being a
two-step imaging proess where the user may obtain excellent quality
in the first imaging step, but then, after the effort and expense
of imaging, the quality of the second lamination step may be
unacceptable. Also, this two step imaging process requires the user
to have the equipment for the second lamination step. It would be
advantageous to have a one step imaging process for ink jet
printing on ink jet ink printing media having rough, non-uniform
substrates.
[0008] A method for preparing articles, such as electrochemical
cells and ink jet printing media, which can avoid the foregoing
problems often encountered with preparing articles comprising a
microporous layer, particularly those comprising a microporous
xerogel layer, would be of great value.
SUMMARY OF THE INVENTION
[0009] The present invention pertains to methods of preparing an
article comprising a microporous layer, which methods comprise the
steps of (a) coating a microporous layer on a temporary carrier
substrate to form a microporous layer assembly, wherein the
microporous layer has a first surface in contact with the temporary
carrier substrate and has a second surface on the side opposite
from the temporary carrier substrate; (b) laminating the second
surface of the microporous layer to a substrate to form a
microporous layer/substrate assembly; and (c) removing the
temporary carrier substrate from the first surface of the
microporous layer to form the article. In a preferred embodiment,
the microporous layer comprises one or more microporous xerogel
layers. In one embodiment, the microporous layer assembly further
comprises one or more non-microporous coating layers, wherein the
one or more non-microporous coating layers are in contact with at
least one of the one or more microporous xerogel layers of the
microporous layer. In one embodiment, one of the one or more
microporous xerogel layers of the microporous layer is coated
directly on the temporary carrier substrate. In one embodiment, one
of the one or more non-microporous coating layers of the
microporous layer assembly is coated directly on the temporary
carrier substrate prior to coating the microporous layer, and the
microporous layer is then coated on a surface of the one of the one
or more non-microporous coating layers, which surface is on the
side of the one of the one or more non-microporous coating layers
opposite from the temporary carrier substrate, and further wherein
the temporary carrier substrate is removed in step (c) from a
surface of the one of the one or more non-microporous coating
layers, which surface is on the side of the one of the one or more
non-microporous coating layers opposite from the microporous layer.
In one embodiment, one of the one or more non-microporous coating
layers of the microporous layer assembly is coated after step (a)
directly on the surface of the microporous layer, which surface is
on the side of the microporous layer opposite from the temporary
carrier substrate layer, prior to laminating to the substrate in
step (b).
[0010] In a preferred embodiment, at least one of the one or more
microporous xerogel layers comprises a xerogel material selected
from the group consisting of pseudo-boehmites, zirconium oxides,
titanium oxides, aluminum oxides, silicon oxides, and tin oxides.
In one embodiment, the microporous layer comprises a microporous
material prepared by vesiculation of an organic polymer layer, and
wherein said vesiculation comprises a step of photolyzing or
heating a gas forming compound. In one embodiment, the gas forming
compound is an aromatic diazonium compound.
[0011] In one embodiment of the methods of preparing an article
comprising a microporous layer of the present invention, the
temporary carrier substrate is a flexible web substrate. Suitable
web substrates include, but are not limited to, papers, polymeric
films, and metals. In one embodiment, the flexible web substrate is
surface treated with a release agent.
[0012] In one embodiment, the microporous layer assembly is a
cathode/separator assembly, the substrate is an anode assembly, and
the article is an electrochemical cell. The electrochemical cell
may be a primary cell or a secondary cell. In one embodiment, the
article is an electrochemical cell comprising a cathode, an anode,
and a separator interposed between the cathode and the anode,
wherein the separator comprises a microporous xerogel layer, which
xerogel layer comprises zirconium oxide.
[0013] In one embodiment, the microporous layer assembly is an ink
jet ink-receptive coating assembly, the substrate is a flexible web
substrate, and the article is an ink jet ink printing media.
[0014] In one embodiment, the microporous layer assembly is an
ultrafiltration layer assembly, the substrate is a flexible web
substrate, and the article is a filtration media.
[0015] In one embodiment, the microporous layer assembly is a
separator, the substrate is a first electrode assembly, and the
article is a first electrode/separator assembly. In one embodiment,
the methods further comprise the step of combining the first
electrode/separator assembly with a second electrode assembly to
prepare an electrochemical cell, a capacitor, or a fuel cell. In
one embodiment, the microporous layer assembly is a separator for
use in an electrochemical cell, wherein the separator comprises a
microporous xerogel layer, which xerogel layer comprises zirconium
oxide.
[0016] Another aspect of the present invention pertains to an
article prepared by the methods of this invention, as described
herein. In one embodiment, the article is a separator comprising a
microporous layer, wherein the separator is prepared according to a
method comprising the steps of (a) coating a microporous layer on a
temporary carrier substrate to form a microporous layer assembly,
wherein the microporous layer has a first surface in contact with
the temporary carrier substrate and has a second surface on the
side opposite from the temporary carrier substrate; (b) coating an
overlying layer on the second surface of the microporous layer,
wherein the overlying layer has a first surface in contact with the
second surface of the microporous layer and has a second surface on
the side opposite from the microporous layer, and (c) removing the
temporary carrier substrate from the first surface of the
microporous layer to form the separator, wherein the microporous
layer comprises one or more microporous xerogel layers and wherein
at least one of the one or more microporous xerogel layers
comprises a zirconium oxide xerogel material. In one embodiment,
the article is an electrochemical cell comprising a cathode, an
anode, and a separator comprising a microporous layer interposed
between the cathode and the anode, wherein the separator is
prepared as described herein. In a preferred embodiment, the
article is an ink jet ink printing media.
[0017] As will be appreciated by one of skill in the art, features
of one aspect or embodiment of the invention are also applicable to
other aspects or embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows a representative process flow diagram with
cross-sectional views of one embodiment of the methods of preparing
an article of the present invention, which comprises a
non-microporous coating layer step 41, a lamination step 60, and a
temporary carrier substrate removing step 70, starting with a
microporous layer assembly 15 comprising a temporary carrier layer
2, a non-microporous coating layer 101, and a microporous layer
102.
[0019] FIGS. 2A and 2B show representative process flow diagrams
with cross-sectional views of two other embodiments of the methods
of preparing an article of this invention, which comprises, for
FIG. 2A, a lamination step 80 prior to the temporary carrier
substrate removing step 70; and which comprises, for FIG. 2B, a
lamination coating step 80 and a slitting step 95 prior to the
temporary carrier substrate removing step 70, where these steps are
done starting with a microporous layer assembly 24 comprising a
temporary carrier substrate 2, a microporous layer 102, and two
different non-microporous coating layers 201 and 301.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Many microporous coatings, particularly microporous xerogel
coatings which are typically subject to a high level of stresses
and potential cracking during drying, formation, and mechanical
handling of the three-dimensional gel structure in the microporous
layer, are difficult to obtain at the desired quality level when
coated on surfaces which are rough and non-uniform or which have
poor mechanical strength and flexibility properties. A rough and
non-uniform coating surface may cause a wide variation in the
thicknesses of microporous coatings applied to this surface.
Besides possibly causing the formation of sections of the
microporous coating layer which are too thin for the desired
application, these thickness variations may interfere with the
desired level and uniformity of the microporosity and with the
mechanical strength and cracking resistance of the microporous
layer. This is particularly true when the thickness of the
microporous coating layer is significantly above that needed for
the desired application. Also, a coating surface with poor
mechanical strength and flexibility may induce, for example,
stresses, mechanical failure, poor adhesion, and cracking in a
microporous layer coated on this surface. Examples of applications
for microporous coatings, including microporous xerogel coatings,
where a relatively smooth surface and a mechanically strong layer
on which to apply and form the microporous coating would be useful,
include, but are not limited to, microporous separators for contact
to one or more electrodes of an electrochemical cell, capacitor, or
fuel cell; microporous ink jet ink-receptive layers for contact to
a wide variety of rough, uneven support surfaces such as papers,
fabrics, canvas, and spun-woven plastics; and microporous
filtration layers for contact to a wide variety of rough, uneven
substrates such as papers. For example, for the product application
of microporous separators involving contact to the positive
electrode or cathode of an electrochemical cell, the roughness and
non-uniformity of the cathode surface prior to coating the
microporous separator layer on it may be reduced, for example, by
calendering the cathode surface or by applying a thin uniform
coating to the cathode surface. However, the reduction of the
roughness and non-uniformity of the cathode surface by these
approaches may still not be sufficient and also may not prevent
undesirable results from poor mechanical strength and flexibility
of the cathode and from penetration of the separator coating into
porous areas of the cathode during the coating application
process.
[0021] The present invention overcomes these limitations for
preparing microporous coatings for a wide variety of applications,
such as separators for use in electrochemical cells, ink jet
ink-receptive media, filtration materials, and other product
applications. One aspect of the present invention pertains to
methods of preparing an article, which methods comprise the steps
of (a) coating a microporous layer on a temporary carrier
substrate, (b) coating any other desired layers in desired coating
patterns built up on the surface of the microporous layer on the
side opposite from the temporary carrier substrate, (c) laminating
the microporous layer assembly resulting from steps (a) and (b) to
a desired substrate, such as an anode assembly comprising an anode
active layer, and (d) removing the temporary carrier substrate from
the microporous separator layer before step (c) or, alternatively,
after step (c). A lamination process similar to that of step (c)
may be utilized in step (b) to coat the microporous layer by a
lamination step of applying an assembly comprising, for example, a
cathode active layer of the cathode to the surface of the
microporous layer on the side opposite from the temporary carrier
substrate, wherein the cathode active layer has a first surface in
contact with the surface of the microporous layer and has a second
surface on the side opposite from the temporary carrier substrate.
In one embodiment of the lamination process in step (b), the
assembly comprising, for example, the cathode active layer, further
comprises a second temporary carrier substrate, and wherein,
subsequent to step (b), there is a step of removing the second
temporary carrier substrate from the assembly comprising the
cathode active layer.
[0022] This method of applying a microporous layer to a temporary
carrier substrate, subsequent coating of one or more other layers
overlying the microporous layer, and the subsequent removal of the
temporary carrier substrate from the microporous layer is
particularly useful when the microporous layer comprises one or
more microporous xerogel layers. Besides applications in electric
current producing cells, this method may be readily adapted for a
wide variety of other product applications, including ink jet
ink-receptive media and filtration materials, where microporous
coating layers may be utilized.
[0023] The surface of the temporary carrier substrate is selected
to have the smoothness, mechanical strength, flexibility, and
porosity properties that are desirable for the preparation of the
microporous layer by coating on the surface of the temporary
carrier substrate and to also have the suitable release properties
for removal of the temporary carrier substrate. This method of
applying a microporous layer to a temporary carrier substrate,
subsequent coating and/or lamination of one or more other layers
overlying the microporous layer, and the subsequent removal of the
temporary carrier substrate from the microporous layer is
particularly useful when the microporous layer comprises one or
more microporous xerogel layers. Besides applications in
electrochemical cells, this method may be readily adapted for a
wide variety of other product applications, including ink jet
ink-receptive media and filtration materials, where microporous
coating layers may be utilized.
[0024] One embodiment of the methods of the present invention is
illustrated in FIG. 1. Referring to FIG. 1, in a non-microporous
coating step 41, a non-microporous coating layer 103 is coated onto
a surface of a microporous layer assembly 15 comprising a temporary
carrier substrate 2, a non-microporous coating layer 101, and
microporous layer 102, thereby forming microporous layer assembly
18. Next, in a lamination step 60, a substrate 201 is laminated
onto the surface of the non-microporous coating layer 103 to form
microporous layer/substrate assembly 19 comprising temporary
carrier substrate 2, non-microporous coating layer 101, microporous
layer 102, non-microporous coating layer 103, and substrate 201.
Following this step, in a temporary carrier substrate removing step
70, the temporary carrier substrate 2 is removed from the
microporous layer 102 of microporous layer/substrate assembly 19 to
form an article 20 comprising non-microporous coating layer 101,
microporous layer 102, non-microporous coating layer 103, and
substrate 201.
[0025] The term "electrochemical cell," as used herein, pertains to
an article that produces an electric current through an
electrochemical reaction and that comprises a positive electrode or
cathode, a negative electrode or anode, and an electrolyte element
interposed between the anode and the cathode, wherein the
electrolyte element comprises a separator layer and an aqueous or
non-aqueous electrolyte in pores of the separator layer.
Electrochemical cells may be primary or secondary cells.
[0026] The term "microporous" as used herein, pertains to the
material of a layer, which material possesses pores of diameter of
about 1 micron or less which are interconnected in a substantially
continuous fashion from one outermost surface of the layer through
to the other outermost surface of the layer. The term "microporous
layer" is used herein to describe a layer, which layer may comprise
one or more discrete coating layers, where the layer as a whole is
microporous. Examples of microporous materials useful in the
microporous separator layer of the methods of the present invention
include, but are not limited to, inorganic xerogel layers or films,
inorganic xerogel layers or films further comprising an organic
polymer, and organic polymer layers or films that undergo
vesiculation or pore formation upon gas formation, for example, by
heating or photoirradiating an aromatic diazonium compound or other
gas forming compound, as known for example in the art of preparing
vesicular microfilm.
[0027] The terms "non-microporous layer" and "non-microporous
coating layer" are used herein to pertain to a layer, which layer
may comprise one or more discrete coating layers, where the layer
as a whole is not microporous.
[0028] In one embodiment of the methods of preparing an article of
this invention, the microporous layer comprises one or more
microporous xerogel layers. By the terms "xerogel layer" and
"xerogel structure," as used herein, is meant, respectively, a
layer of a coating or the structure of a coating layer in which the
layer and structure were formed by drying a liquid sol or sol-gel
mixture to form a solid gel matrix as, for example, described in
Chem. Mater., Vol. 9, pages 1296 to 1298 (1997) by Ichinose et al.
for coating layers of metal-oxide based xerogels. Thus, if the
liquid of the gel formed in the liquid sol-gel mixture is removed
substantially, for example, though formation of a liquid-vapor
boundary phase, the resulting gel layer or film is termed, as used
herein, a xerogel layer. As the liquid is removed from the gel in
the liquid sol-gel mixture by, for example, evaporation, large
capillary forces are exerted on the pores, forming a collapsed
structure for the xerogel layer. The pore sizes of the xerogel
layer and structure are very small, having average pore diameters
less than 300 nm or 0.3 microns.
[0029] Thus, the microporous xerogel layer of the methods of this
invention comprises a dried microporous three-dimensional solid gel
network with pores which are interconnected in a substantially
continuous fashion from one outermost surface of the layer through
to the other outermost surface of the layer. A continuous xerogel
coating layer has the materials of the xerogel in a continuous
structure in the coating layer, i.e., the materials are in contact
and do not have discontinuities in the structure, such as a
discontinuous layer of solid pigment particles that are separated
from each other. In contrast, xerogel pigment particles may be
formed by a xerogel process involving drying a liquid solution of a
suitable precursor to the pigment to form a dried mass of xerogel
pigment particles, which is typically then ground to a fine powder
to provide porous xerogel pigment particles. The terms "xerogel
coating" and "xerogel coating layer," as used herein, are
synonymous with the term "xerogel layer".
[0030] The term "binder," as used herein, pertains to inorganic or
organic materials which form a continuous structure or film in a
substantially continuous fashion from one outermost surface of a
coating layer through to the other outermost surface of the coating
layer. As such, for example, the xerogel, such as pseudo-boehmite
or other metal oxide xerogel, of a xerogel layer is also a binder
in addition to having a xerogel structure with ultrafine pores.
[0031] A wide variety of materials known to form microporous
xerogel layers when coated on a surface may be used to provide the
microporous layers for the methods of the present invention. The
electrical conductivity of the microporous separator layer of the
methods of the present invention must be low enough to provide the
necessary insulating properties for the separator component when
used in an electric current producing cell. Thus, for example, a
highly electrically conductive material, such as some vanadium
oxides, that may form in microporous xerogel layers when coated
from a sol-gel liquid mixture of a suitable precursor onto a
surface may not be suitable in the methods of this invention.
Suitable materials for use in the microporous xerogel layers of the
microporous layer of the methods of the present invention include,
but are not limited to, pseudo-boehmites, zirconium oxides,
titanium oxides, aluminum oxides, silicon oxides, and tin
oxides.
[0032] In a preferred embodiment of the methods of preparing an
article of this invention, the microporous layer comprises one or
more microporous pseudo-boehmite layers. Microporous
pseudo-boehmite layers for use as separators in electrochemical
cells are described in copending U.S. patent application Ser. Nos.
08/995,089 and 09/215,112, both to Carlson et al. of the common
assignee, the disclosures of which are fully incorporated herein by
reference. The term "pseudo-boehmite," as used herein, pertains to
hydrated aluminum oxides having the chemical formula
Al.sub.2O.sub.3.cndot.xH.sub.2O wherein x is in the range of from
1.0 to 1.5. Terms, as used herein, which are synonymous with
"pseudo-boehmite," include "boehmite," "AlOOH," and "hydrated
alumina." The materials referred to herein as "pseudo-boehmite" are
distinct from anhydrous aluminas (Al.sub.2O.sub.3, such as
alpha-alumina and gamma-alumina), and hydrated aluminum oxides of
the formula Al.sub.2O.sub.3.cndot.xH.sub.2O wherein x is less than
1.0 or greater than 1.5.
[0033] The amount of the pores in a microporous layer may be
characterized by the pore volume, which is the volume in cubic
centimeters of pores per unit weight of the layer. The pore volume
may be measured by filling the pores with a liquid having a known
density and then calculated by the increase in weight of the layer
with the liquid present divided by the known density of the liquid
and then dividing this quotient by the weight of the layer with no
liquid present, according to the equation: 1 Pore Volume = [ W 1 -
W 2 ] / d W 2
[0034] where W.sub.1 is the weight of the layer when the pores are
completely filled with the liquid of known density, W.sub.2 is the
weight of the layer with no liquid present in the pores, and d is
the density of the liquid used to fill the pores. Also, the pore
volume may be estimated from the apparent density of the layer by
subtracting the reciprocal of the theoretical density of the
materials (assuming no pores) comprising the microporous layer from
the reciprocal of the apparent density or measured density of the
actual microporous layer, according to the equation: 2 Pore Volume
= ( 1 d 1 - 1 d 2 )
[0035] where d.sub.1 is the density of the layer which is
determined from the quotient of the weight of the layer and the
layer volume as determined from the measurements of the dimensions
of the layer, and d.sub.2 is the calculated density of the
materials in the layer assuming no pores are present or, in other
words, d.sub.2 is the density of the solid part of the layer as
calculated from the densities and the relative amounts of the
different materials in the layer. The porosity or void volume of
the layer, expressed as percent by volume, can be determined
according to the equation: 3 Porosity = 100 ( Pore Volume ) [ Pore
Volume + 1 / d 2 ]
[0036] where pore volume is as determined above, and d.sub.2 is the
calculated density of the solid part of the layer, as described
above.
[0037] In one embodiment, the microporous xerogel layer of the
microporous layer of the methods of the present invention has a
pore volume from 0.02 to 2.0 cm.sup.3/g. In a preferred embodiment,
the microporous xerogel layer has a pore volume from 0.3 to 1.0
cm.sup.3/g. In a more preferred embodiment, the microporous xerogel
layer has a pore volume from 0.4 to 0.7 cm.sup.3/g.
[0038] The microporous xerogel layers of the microporous layer of
the methods of the present invention have pore diameters which
range from 0.3 microns down to less than 0.002 microns. In one
embodiment, the microporous xerogel layer has an average pore
diameter from 0.001 microns or 1 nm to 0.3 microns or 300 nm. In a
preferred embodiment, the microporous xerogel layer has an average
pore diameter from 0.001 microns or 1 nm to 0.030 microns or 30 nm.
In a more preferred embodiment, the microporous xerogel layer has
an average pore diameter from 0.003 microns or 3 nm to 0.010
microns or 10 nm.
[0039] One distinct advantage of microporous layers with much
smaller pore diameters on the order of 0.001 to 0.03 microns is
that insoluble particles, even colloidal particles with diameters
on the order of 0.05 to 1.0 microns, can not pass through the
microporous layer because of the ultrafine pores. In contrast, for
example, colloidal particles, such as conductive carbon powders
often incorporated into cathode compositions of electrochemical
cells, may readily pass through conventional microporous layers,
such as microporous polyolefins, and thereby may migrate to
undesired areas of the cell.
[0040] Another significant advantage of the microporous layer
comprising one or more microporous xerogel layers of the methods of
the present invention is that the nanoporous structure of the
xerogel layer may function as an ultrafiltration membrane and, in
addition to blocking all particles and insoluble materials, may
block or significantly inhibit the diffusion of soluble materials
of relatively low molecular weights, such as 2,000 or higher, while
permitting the diffusion of soluble materials with molecular
weights below this cutoff level. This property may be utilized to
advantage in coating other layers onto the surface of the
microporous layer by preventing any undesired penetration of
pigments and other materials into the microporous layer. For
example, with electrochemical cells, this property may also be
utilized to advantage in selectively impregnating or imbibing
materials into the microporous separator layer during manufacture
of the electrochemical cell or in selectively permitting diffusion
of very low molecular weight materials through the microporous
separator layer during all phases of the operation of the cell
while blocking or significantly inhibiting the diffusion of
insoluble materials or of soluble materials of medium and higher
molecular weights.
[0041] Another important advantage of the extremely small pore
diameters of the microporous xerogel layer of the microporous layer
of the methods of the present invention is the strong capillary
action of the tiny pores in the xerogel layer which enhances the
capability of the microporous layers to readily take up or imbibe
liquids, such as electrolyte liquids and ink jet ink liquids, and
to retain these liquids in pores within the microporous layer.
[0042] The microporous layers of the methods of this invention may
optionally further comprise a variety of binders (in addition to
the binder, such as for example a pseudo-boehmite xerogel, that
provides the primary microporous structure of the separator layer),
to improve the mechanical strength and other properties of the
layer, as for example, described for microporous pseudo-boehmite
xerogel layers for microporous separator layers in the two
aforementioned copending U.S. patent application Ser. Nos.
08/995,089 and 09/215,112, both to Carlson et al. of the common
assignee. Any binder that is compatible with the microporous
material of the microporous layer may be used. For microporous
xerogel layers, any binder that is compatible with the xerogel
precursor sol during mixing and processing into the microporous
xerogel layer and provides the desired mechanical strength and
uniformity of the layer without significantly interfering with the
desired microporosity is suitable for use. The preferred amount of
binder is from 5% to 70% of the weight of the xerogel-forming
material in the layer. Below 5 weight percent, the amount of binder
is usually too low to provide a significant increase in mechanical
strength. Above 70 weight percent, the amount of binder is usually
too high and fills the pores to an excessive extent, which may
interfere with the microporous properties and with the transport of
low molecular weight materials through the layer. The binder may be
inorganic, for example, another xerogel-forming material, such as
silicas, gamma aluminum oxides, and alpha aluminum oxides, that are
known to be compatible with the primary xerogel-forming material,
such as pseudo-boehmite, present in the microporous layer, for
example, as is known in the art of ink-receptive microporous
xerogel layers for ink jet printing. In one embodiment, the binders
in the microporous xerogel layer are organic polymer binders.
Examples of suitable binders include, but are not limited to,
polyvinyl alcohols, cellulosics, polyvinyl butyrals, urethanes,
polyethylene oxides, copolymers thereof, and mixtures thereof.
Binders may be water soluble polymers and may have ionically
conductive properties. Suitable binders may also comprise
plasticizer components such as, but not limited to, low molecular
weight polyols, polyalkylene glycols, and methyl ethers of
polyalkylene glycols to enhance the coating, drying, and
flexibility of the microporous xerogel layer.
[0043] The thickness of the microporous layer of the methods of the
present invention may vary over a wide range since the basic
properties of microporosity and mechanical integrity are present in
layers of a few microns in thickness as well as in layers with
thicknesses of hundreds of microns. The microporous layer may be
coated in a single coating application or in multiple coating
applications to provide the desired overall thickness. For various
reasons including cost, overall performance properties of the
microporous layer, and ease of manufacturing, the desirable overall
thicknesses of the microporous layer are typically in the range of
1 micron to 25 microns. Preferred are thicknesses in the range of 1
micron to 20 microns. More preferred are thicknesses in the range
of 5 to 15 microns. Conventional separators, such as the porous
polyolefin materials, are typically 25 to 50 microns in thickness
so it is particularly advantageous that the microporous separator
layers of this invention can be effective and inexpensive at
thicknesses below 15 microns.
[0044] In the methods of preparing an article of the present
invention, the temporary carrier substrate functions as a temporary
support to the superposed layers during the process steps of this
invention and may be any web or sheet material possessing suitable
smoothness, flexibility, dimensional stability, and adherence
properties in the microporous layer assembly. In one embodiment of
the methods of preparing an article of the present invention, the
temporary carrier substrate is a flexible web substrate. Suitable
web substrates include, but are not limited to, papers, polymeric
films, and metals. A typical flexible polymeric film for use as the
temporary carrier substrate is a polyethylene terephthalate film.
In a preferred embodiment, the flexible web substrate is surface
treated with a release agent to enhance desired release
characteristics, such as by treatment with a silicone release
agent. This surface treatment or coating with a release agent of
the temporary carrier substrate may be done on a multistation
coating machine in the same coating pass as that used to later
apply the first layer of the microporous layer assembly in the
methods of this invention. Examples of suitable flexible web
substrates include, but are not limited to, resin-coated papers
such as papers on which a polymer of an olefin containing 2 to 10
carbon atoms, such as polyethylene, is coated or laminated; and
transparent or opaque polymeric films such as polyesters,
polypropylene, polystyrene, polycarbonates, polyvinyl chloride,
polyvinyl fluoride, polyacrylates, and cellulose acetate. The
temporary carrier substrate may be of a variety of thicknesses,
such as, for example, thicknesses in the range of 2 to 100
microns.
[0045] One benefit is that the temporary carrier substrate, after
its removal from the microporous layer/substrate assembly, may be
reused for preparing another article, may be reused for a different
product application, or may be reclaimed and recycled. Any such
reuses combine to lower the effective cost of the temporary carrier
substrate in preparing the article.
[0046] In a preferred embodiment of the methods of preparing an
article of the present invention, the microporous layer comprises
one or more microporous xerogel layers, and more preferably, the
microporous layer assembly further comprises one or more
non-microporous coating layers, wherein the one or more
non-microporous coating layers are in contact with at least one of
the one or more microporous xerogel layers. In one embodiment, one
of the one or more microporous xerogel layers of the microporous
layer is coated directly on the temporary carrier substrate. In one
embodiment, one of the one or more non-microporous coating layers
of the microporous layer assembly is coated directly on the
temporary carrier substrate.
[0047] The incorporation of one or more non-microporous coating
layers in the microporous layer assembly of the methods of this
invention may enhance the mechanical strength and add flexibility
to the microporous layer comprising one or more discrete
microporous layers, particularly those microporous layers
comprising one or more microporous xerogel layers. The
non-microporous coating layers may also provide specific functional
properties to the article, such as adhesion to the substrate,
ability to absorb specific liquids, and specific gloss, opacity,
and other optical properties. The thickness of the non-microporous
coating layers of the microporous layer assembly of the methods of
this invention may vary over a wide range, such as, but not limited
to, from 0.2 microns to 200 microns.
[0048] To achieve the desired coating properties, the one or more
non-microporous coating layers may comprise polymers, pigments, and
other materials known in the art of non-microporous coatings,
especially those known for use in flexible and durable coatings.
Examples of other coating materials include, but are not limited
to, photosensitizers for radiation curing of any monomers and
macromonomers present; catalysts for non-radiation curing of any
monomers, macromonomers, or polymers present; crosslinking agents
such as zirconium compounds, aziridines, and isocyanates;
surfactants; plasticizers; dispersants; flow control additives; and
rheology modifiers.
[0049] The microporous layer assembly of the methods of the present
invention may have more than one microporous layer. Also, the
microporous layer assembly of the methods of the present invention
may have more than one non-microporous coating layer. The
compositions of these multiple microporous layers may be the same
or different for each such layer in the microporous layer assembly.
Also, the compositions of these multiple non-microporous coating
layers may be the same or different for each such layer in the
microporous layer assembly. The many possible combinations of
microporous layers and non-microporous coating layers also include
a non-microporous coating layer intermediate between two
microporous layers.
[0050] In one embodiment, the step of removing the temporary
carrier substrate occurs prior to or, alternatively, subsequent to
a slitting step, for example, as illustrated in FIGS. 2A and 2B.
Referring to FIG. 2A, in a lamination step 80, a substrate 401 is
laminated to a microporous layer assembly 24 comprising a temporary
carrier substrate 2, a microporous layer 102, and two different
non-microporous coating layers 201 and 301. This step 80 forms
microporous layer/substrate assembly 27 comprising substrate 401,
non-microporous coating layers 201 and 301, microporous layer 102,
and temporary carrier substrate 2. Next, in a temporary carrier
substrate removing step 70, the temporary carrier substrate 2 is
removed from the microporous layer 102 of microporous
layer/substrate assembly 27 to form article 28 comprising substrate
401, non-microporous coating layers 201 and 301, and microporous
layer 102. If a smaller dimension is desired for article 28, in a
slitting step 95, article 28 may be cut or slit to form multiples
of article 32 comprising substrate 401, non-microporous coating
layers 201 and 301, and microporous layer 102. Referring to FIG.
2B, this is similar to FIG. 2A except that the sequence of the
slitting step 95 and the temporary carrier substrate removing step
70 are reversed. In both FIG. 2A and FIG. 2B, the final product is
article 32.
[0051] The various coating layers in the methods of preparing a
microporous layer assembly of the present invention may be coated
from a liquid mixture comprising a liquid carrier medium and the
solid materials of the layer which are dissolved or dispersed in
the liquid carrier medium. The choice of the liquid carrier medium
may vary widely and includes water, organic solvents, and blends of
water and organic solvents. Exemplary organic solvents include, but
are not limited to, alcohols, ketones, esters, and hydrocarbons.
The choice of the liquid carrier medium depends mainly on the
compatibility with the particular solid materials utilized in the
specific coating layer, on the type of method of coating
application to the receiving surface, and on the requirements for
wettability and other coating application properties of the
particular receiving surface for the coating. For example, for
coating a microporous xerogel layer, the liquid carrier medium is
typically water or a blend of water with an alcohol solvent, such
as isopropyl alcohol or ethyl alcohol, since the sol-gel materials
that dry and condense to form the xerogel layer typically are most
compatible with a water-based, highly polar liquid carrier
medium.
[0052] The application of the liquid coating mixture to the
temporary carrier substrate or other layer may be done by any
suitable process, such as the conventional coating methods, for
example, of wire-wound rod coating, spray coating, spin coating,
reverse roll coating, gravure coating, slot extrusion coating, gap
blade coating, and dip coating. The liquid coating mixture may have
any desired solids content that is consistent with the viscosity
and rheology that is acceptable in the coating application method.
After the liquid coating mixture is applied on the temporary
carrier substrate or other layer, the liquid carrier medium is
typically removed to provide a dried, solid coating layer. This
removal of the liquid carrier medium may be accomplished by any
suitable process, such as conventional methods of drying, for
example, hot air at a high velocity or exposure to ambient air
conditions. Some layers of the microporous layer assembly of the
present invention such as, for example, non-microporous current
collector layers, may be formed by techniques such as vacuum
deposition, ion-sputtering, vacuum flash evaporation, and other
methods as known in the art.
[0053] A wide variety of articles comprising a microporous layer
may be prepared by utilizing the methods of the present invention.
Suitable articles for preparation by the methods of this invention
include, but are not limited to, electrochemical cells, separators,
capacitors, fuel cells, ink jet printing and other imaging media,
and filtration media. In the case of electric current producing
articles such as electrochemical cells, capacitors, and fuel cells,
which typically have two electrodes and a microporous separator or
membrane layer interposed between the two electrodes, the
microporous layer assembly may be a first electrode/separator
assembly, the substrate may be a second electrode assembly such as
a second electrode on a second temporary carrier substrate, and the
article may be the electrochemical cell, capacitor, or fuel cell
depending on the specific electrodes, separator, and other
components utilized, as known in the art of these various electric
current producing articles. Alternatively, the microporous layer
assembly may be a separator, the substrate may be a first electrode
assembly such as a cathode assembly or an anode assembly, and the
article may be a first electrode/separator assembly such as a
cathode/separator assembly.
[0054] For ink jet printing media, the microporous layer assembly
may be an ink jet ink-receptive coating assembly such as one of the
single or multiple coating layer designs comprising a microporous
layer as known in the art of ink jet printing media, the substrate
may be a flexible web substrate such as cloth, canvas, paper, and
non-woven plastics, and the article is an ink jet printing
media.
[0055] For filtration media, the microporous layer assembly may be
an ultrafiltration layer assembly such as a single or multiple
coating layer designs comprising at least one microporous layer as
known in the art of filtration media, the substrate may be a
flexible web substrate such as a paper, and the article is a
filtration media. The methods of this invention are particularly
advantageous for preparing filtration media since the
ultrafiltration properties of a microporous xerogel layer may be
placed next to the paper surface by the lamination step to the
rough surface of the paper with the option of coarser filtration
layers on the side of the xerogel layer opposite to the paper.
Direct coating of the microporous xerogel layer on the rough paper
substrates typically used in filtration media would be extremely
difficult to achieve if the full ultrafiltration properties of the
xerogel layer are required.
[0056] Another aspect of the present invention pertains to articles
prepared according to the methods of the present invention, as
described herein. Thus, the articles of the present invention
comprise a microporous layer, which articles are prepared according
to the methods of this invention. Examples of such articles
include, but are not limited to, electrochemical cells, separators,
ink jet printing media, filtration media, electrode/separator
assemblies, capacitors, and fuel cells, as described herein.
EXAMPLES
[0057] Several embodiments of the present invention are described
in the following example, which are meant by way of illustration
and not by way of limitation.
Example 1
[0058] A coating mixture for a microporous ink jet ink-receptive
layer was prepared by adding 23.8 g of a 13.5% by weight solids
solution of boehmite sol in water (DISPAL 11N7-12, a trademark for
aluminum boehmite sols available from CONDEA Vista company,
Houston, Tex.) to 14.2 g of a 4% by weight solution of polyvinyl
alcohol (AIRVOL 125, a trademark for polyvinyl alcohol polymers
available from Air Products, Inc. Allentown, Pa.) in water and
stirring to mix the materials. 0.05 g of FLUORAD FC-430, a
trademark for non-ionic fluorochemical surfactants available from
3M Corporation, St. Paul, Minn., was added with stirring to make
the final microporous coating mix. Using a gap coating with a
doctor blade and a hand coating process, the microporous coating
mix was applied to the non-treated surface of 23 micron thick
MELINEX 6328, a trademark for polyethylene terephthalate (PET)
films available from DuPont Teijin Films, Wilmington, Del. After
air drying in a laboratory hood under a high rate of air
circulation, a smooth and uniform microporous ink jet ink-receptive
layer with a dry thickness of 14 microns was formed on the PET film
substrate.
[0059] A non-microporous coating layer of polyethylene oxide
(900,000 MW from Aldrich Chemical Company, Milwaukee, Wis.) was
prepared by coating a 2% by weight solution in water onto the
microporous ink jet ink-receptive layer using the gap coating bar
with a doctor blade. After drying at 130.degree. C. in a convection
oven, a uniform non-microporous coating layer with a dry thickness
of 5 microns was formed on the microporous layer.
[0060] The resulting microporous layer assembly of PET film as the
temporary carrier substrate, the microporous ink jet ink-receptive
layer, and the non-microporous coating layer was then laminated to
a sheet of standard grade xerographic bond paper by using a
pressure roller process with the surface of the non-microporous
coating layer in contact to the paper. Following this lamination
step, the PET film, which had a low level of adhesion to the
microporous layer, was easily removed by delamination and peeling
off the PET film. The resulting ink jet printing media article
comprising the paper substrate, the non-microporous coating layer,
and the microporous ink jet ink-receptive layer on its outer
surface with the non-microporous coating layer now interposed
between the microporous layer and the substrate, was imaged on an
HP 861 color ink jet ink printer (a trademark for products from
Hewlett Packard Corporation, Palo Alto, Calif.). The resulting
color quality and rate of drying of the ink was excellent. Because
the top surface of the microporous layer had orginally been coated
on the smooth PET film, this top surface of the microporous layer
was very smooth and had a high gloss, which is a very desirable
feature for ink jet printing, particularly for digital photographic
applications.
[0061] While the invention has been described in detail and with
reference to specific and general embodiments thereof, it will be
apparent to one skilled in the art that various changes and
modifications can be made therein without departing from the spirit
and scope thereof.
* * * * *