U.S. patent application number 13/510627 was filed with the patent office on 2012-09-13 for assemblies comprising a polyimide film and an electrode, and methods relating thereto.
This patent application is currently assigned to E. I DU PONT DE NEMOURS AND COMPANY. Invention is credited to Brian C. Auman, Meredith L. Dunbar, Tao He, Kostantinos Kourtakis.
Application Number | 20120227790 13/510627 |
Document ID | / |
Family ID | 43458223 |
Filed Date | 2012-09-13 |
United States Patent
Application |
20120227790 |
Kind Code |
A1 |
Auman; Brian C. ; et
al. |
September 13, 2012 |
ASSEMBLIES COMPRISING A POLYIMIDE FILM AND AN ELECTRODE, AND
METHODS RELATING THERETO
Abstract
The assemblies of the present disclosure comprise an electrode,
and a polyimide film. The polyimide film comprises a sub-micron
filler and a polyimide. The polyimide is derived from at least one
aromatic dianhydride component selected from rigid rod dianhydride,
non-rigid rod dianhydride and combinations thereof, and at least
one aromatic diamine component selected from rigid rod diamine,
non-rigid rod diamine and combinations thereof. The mole ratio of
dianhydride to diamine is 48-52:52-48 and the ratio of X:Y is
20-80:80-20 where X is the mole percent of rigid rod dianhydride
and rigid rod diamine, and Y is the mole percent of non-rigid rod
dianhydride and non-rigid rod diamine. The sub-micron filler is
less than 550 nanometers in at least one dimension; has an aspect
ratio greater than 3:1; is less than the thickness of the film in
all dimensions.
Inventors: |
Auman; Brian C.; (Avondale,
PA) ; Dunbar; Meredith L.; (Canal Winchester, OH)
; He; Tao; (Wilmington, DE) ; Kourtakis;
Kostantinos; (Media, PA) |
Assignee: |
E. I DU PONT DE NEMOURS AND
COMPANY
Wilmington
DE
|
Family ID: |
43458223 |
Appl. No.: |
13/510627 |
Filed: |
November 19, 2010 |
PCT Filed: |
November 19, 2010 |
PCT NO: |
PCT/US10/57397 |
371 Date: |
May 18, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61263266 |
Nov 20, 2009 |
|
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|
Current U.S.
Class: |
136/249 ;
136/252; 136/258; 136/260; 136/262; 136/264 |
Current CPC
Class: |
C08G 73/1067 20130101;
H01L 2924/01079 20130101; H05K 1/0373 20130101; C08G 73/105
20130101; H01L 23/295 20130101; H01L 23/482 20130101; C08G 73/1046
20130101; C08J 2379/08 20130101; H01L 24/12 20130101; H01L
2224/02335 20130101; C08L 79/08 20130101; H01L 2924/12032 20130101;
Y10T 428/257 20150115; H05K 1/0346 20130101; C08K 2201/016
20130101; H01L 2924/01019 20130101; H01L 23/293 20130101; H01L
2924/12032 20130101; H01L 2924/01322 20130101; H01L 2924/01012
20130101; H01L 2224/0401 20130101; H01L 2924/0102 20130101; C08K
7/08 20130101; H01L 2224/0233 20130101; C08K 7/00 20130101; H01L
2924/14 20130101; H01L 2924/00 20130101; H01L 2224/0236 20130101;
C08G 73/1042 20130101; H01L 2224/16227 20130101; H01L 2224/02319
20130101; H01L 2924/01021 20130101; Y10T 428/259 20150115; Y10T
428/256 20150115; Y10T 428/25 20150115; H05K 2201/0154 20130101;
H01L 2924/01322 20130101; H01L 2224/0231 20130101; C08G 73/1071
20130101; H01L 2924/01057 20130101; H05K 2201/0209 20130101; H01L
2924/09701 20130101; H01L 2224/024 20130101; C08J 5/18 20130101;
C08K 7/04 20130101; C08K 7/02 20130101; H01L 2224/16225 20130101;
H01L 2924/00 20130101 |
Class at
Publication: |
136/249 ;
136/252; 136/262; 136/258; 136/260; 136/264 |
International
Class: |
H01L 31/042 20060101
H01L031/042; H01L 31/0264 20060101 H01L031/0264 |
Claims
1. An assembly comprising: A) a polyimide film having a thickness
from 5 to 150 microns comprising: a) a polyimide derived from: i)
at least one aromatic dianhydride component selected from the group
consisting of: rigid rod dianhydride, non-rigid rod dianhydride and
combinations thereof, ii) at least one aromatic diamine component
selected from the group consisting of: rigid rod diamine, non-rigid
rod diamine and combinations thereof; and wherein the mole ratio of
dianhydride to diamine is 48-52:52-48 and the ratio of X:Y is
20-80:80-20 where X is the mole percent of rigid rod dianhydride
and rigid rod diamine, and Y is the mole percent of non-rigid rod
dianhydride and non-rigid rod diamine based upon the total
dianhydride component and total diamine component of the polyimide;
and b) a sub-micron filler: i) being less than 550 nanometers (as a
numerical average) in at least one dimension; ii) having an aspect
ratio greater than 3:1; iii) being less than the polyimide film
thickness in all dimensions; iv) being present in an amount from 10
to 45 volume percent of the polyimide film; and B) an electrode
supported by the polyimide film.
2. The assembly in accordance with claim 1, further comprising a
light absorber layer; the electrode is between the light absorber
layer and the polyimide film; and the electrode being in electrical
communication with the light absorber layer.
3. The assembly in accordance with claim 2, wherein the light
absorber layer is a CIGS/CIS light absorber layer
4. The assembly in accordance with claim 3, wherein the assembly
further comprises a plurality of monolithically integrated CIGS/CIS
photovoltaic cells.
5. The assembly in accordance with claim 2, wherein the light
absorber layer is amorphous silicon or microcrystalline
silicon.
6. The assembly in accordance with claim 2, wherein the light
absorber layer is CdZnTe, HgCdTe, HgZnTe or HgZnSe.
7. The assembly in accordance with claim 2, wherein the light
absorber layer is CuZnSnS.sub.4 or CuZnSnSe.sub.4.
8. The assembly in accordance with claim 1, wherein the sub-micron
filler is less than 400 nanometers in at least one dimension.
9. The assembly in accordance with claim 1, wherein the sub-micron
filler is selected from a group consisting of oxides, nitrides,
carbides and combinations thereof.
10. The assembly in accordance with claim 1, wherein the sub-micron
filler is acicular titanium dioxide, talc, SiC fiber, platy
Al.sub.2O.sub.3 or mixtures thereof.
11. The assembly in accordance with claim 1, wherein: a) at least
70 mole percent of the aromatic dianhydride component is
pyromellitic dianhydride; and b) at least 70 mole percent of the
aromatic diamine component is 4,4'-diaminodiphenyl ether.
12. The assembly in accordance with claim 1, wherein: the
sub-micron filler is acicular titanium dioxide, talc, SiC fiber,
platy Al.sub.2O.sub.3 or mixtures thereof.
13. The assembly in accordance with claim 1, wherein a) at least 75
mole percent of the aromatic dianhydride component is pyromellitic
dianhydride; and b) 70 mole percent 4,4'-diaminodiphenyl ether and
30 mole percent 1,4 diaminobenzene as the aromatic diamine
component.
14. The assembly in accordance with claim 1 wherein the polyimide
is a block copolymer.
15. The assembly in accordance with claim 14 wherein the block
copolymer is derived from 4,4'-diaminodiphenyl ether and
1,4-diaminobenzene with pyromellitic dianhydride and
3,3',4,4'-biphenyl tetracarboxylic dianhydride.
16. The assembly in accordance with claim 14 wherein the block
copolymer is derived from: a) 10 to 40 mole percent blocks of
pyromellitic dianhydride and 1,4 diaminobenzene; b) 90 to 60 mole
percent blocks of pyromellitic dianhydride and 4,4'-diaminodiphenyl
ether.
17. The assembly in accordance with claim 16, wherein the
sub-micron filler is acicular titanium dioxide, talc, SiC fiber,
platy Al.sub.2O.sub.3 or mixtures thereof.
18. The assembly in accordance with claim 1, wherein the sub-micron
filler is coated with a coupling agent, a dispersant or a
combination thereof.
19. The assembly in accordance with claim 1 wherein the polyimide
is a random copolymer derived from 4,4'-diaminodiphenyl ether and
1,4 diaminobenzene with pyromellitic dianhydride and
3,3',4,4'-biphenyl tetracarboxylic dianhydride.
20. The assembly in accordance with claim 1 wherein the polyimide
is a random copolymer derived from 4,4'-diaminodiphenyl ether and
1,4 diaminobenzene with pyromellitic dianhydride.
Description
FIELD OF DISCLOSURE
[0001] The present disclosure relates generally to assemblies
comprising an electrode, and a polyimide film. More specifically,
the polyimide film comprises a sub-micron filler and a polyimide
polymer having a hybrid backbone structure.
BACKGROUND OF THE DISCLOSURE
[0002] To address an increasing need for alternative energy
sources, there is currently a strong interest in developing
light-weight, efficient photovoltaic systems (e.g., photovoltaic
cells and modules). Broadly speaking, a photovoltaic cell typically
comprises a semiconductor junction device which converts light
energy into electrical energy. A typical photovoltaic cell can be
described as a layered structure having four principal layers: (1)
an absorber-generator (2) a collector-converter (3) a transparent
electrical contact, and (4) an opaque electrical contact. When
light comes in contact with the absorber-generator, the device
generates a voltage differential between the two contacts which
generally increases as the intensity of the light increases.
[0003] The absorber-generator (light absorber layer) is typically a
layer of semiconductor material which absorbs light photons and, as
a consequence, generates minority carriers. Typically, the light
absorber layer captures photons and ejects electrons thus creating
pairs of negatively charged carriers (electrons) and positively
charged carriers ("holes"). If the light absorber layer is a p-type
semiconductor, the electrons are minority carriers, and if it is
n-type, the holes are minority carriers. Minority carriers will be
readily annihilated in the absorber (by recombination with the
plentiful majority carriers), so the minority carriers must be
promptly transported to a collector-converter layer (the
"collector") which is in contact with the absorber layer, wherein
the minority become majority carriers once they enter the collector
layer and can thereby be utilized to power an electrical circuit.
In other words, the collector layer "collects" minority carriers
from the absorber and "converts" them into majority carriers. If
the collector is an oppositely doped region of the same
semiconductor as the light absorber layer, the photovoltaic device
is a p-n junction or homojunction device. If the collector is
comprised of a different semiconductor, the device is a
heterojunction; and, if the collector is metal, the device is a
Schottky junction.
[0004] The transparent contact is a conductive electrical contact
which permits light to pass through to the absorber. It is
typically either a continuous transparent sheet of conductive
material or an open grid of opaque conductive material. If the
transparent contact is on the same side of the photovoltaic device
as the absorber, the device is referred to as being in the front
wall configuration. If the transparent contact is on the opposite
side, the device is said to be in the back wall configuration.
[0005] The advent of silicon junction technology in the 1950's has
permitted the development of high cost, high conversion efficiency
silicon junction photovoltaic cells. Arrays of such devices have
been used with considerable success in the space program. However,
the cost of such devices as energy generators can be very high
relative to conventional electricity generation. A substantial
portion of the high cost is in the preparation of silicon crystals
having sufficient purity and also due to the inefficiencies of the
batch processes by which such cells are fabricated.
[0006] Thin film photovoltaic cells possess many potential
advantages over crystalline silicon (wafer based) cells.
Photovoltaic cells employing thin films (of materials such as: i. a
copper sulfide, copper zinc tin sulfide (CZTS), copper indium
gallium diselenide or disulfide (CIGS), among others as an
absorber; and ii. a cadmium sulfide or the like as a converter) may
be a low cost alternative to silicon crystal based solar cells.
[0007] With CIGS systems, a high temperature deposition/annealing
step is generally applied to improve light absorber layer
performance. The annealing step is typically conducted during
manufacture and is typically applied to an assembly, comprising a
substrate, a bottom electrode and the CIGS light absorber layer.
The substrate requires thermal and dimensional stability at the
annealing temperature(s), and therefore conventional substrates
have typically comprised metal or ceramic (conventional polymeric
materials tend to lack sufficient thermal and dimensional
stability, particularly at peak annealing temperatures). However,
ceramics, such as glass, lack flexibility and can be heavy, bulky
and subject to breakage. Metals can be less prone to such
disadvantages, but metals tend to conduct electricity, which tends
to also be a disadvantage, e.g., inhibits monolithic integration of
CIGS photovoltaic cells.
[0008] Hence, there is an ever increasing interest in the industry
to find a polymer substrate is able to lower overall cost, improve
performance, decrease weight, increase ruggedness and simplify
manufacture. A need therefore exists for reliable thin film solar
cells in a low cost continuous process suitable for large scale
manufacture.
SUMMARY
[0009] The assemblies of the present disclosure comprise a
polyimide film and a electrode supported by the polyimide film. The
polyimide film contains a sub-micron filler and a polyimide. The
polyimide is derived from:
[0010] i) at least one aromatic dianhydride component selected from
the group consisting of rigid rod dianhydride, non-rigid rod
dianhydride and combinations thereof, and
[0011] ii) at least one aromatic diamine component selected from
the group consisting of rigid rod diamine, non-rigid rod diamine
and combinations thereof.
[0012] The mole ratio of dianhydride to diamine is 48-52:52-48 and
the ratio of X:Y is 20-80:80-20 where X is the mole percent of
rigid rod dianhydride and rigid rod diamine, and Y is the mole
percent of non-rigid rod dianhydride and non-rigid rod diamine
based upon the total dianhydride component and total diamine
component of the polyimide.
[0013] The sub-micron filler is less than 550 nanometers (as a
numerical average) in at least one dimension, has an aspect ratio
greater than 3:1, is less than the polyimide film thickness in all
dimensions, and is present in an amount from 10 to 45 volume
percent of the polyimide film. The polyimide film has a thickness
from 5 to 150 microns.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a sectional view of a thin-film solar cell
fabricated on a polyimide film, constructed in accordance with the
present disclosure.
DETAILED DESCRIPTION
Definitions
[0015] "Film" is intended to mean a free-standing film or a
(self-supporting or non self-supporting) coating. The term "film"
is used interchangeably with the term "layer" and refers to
covering a desired area.
[0016] "Monolithic integration" is intended to mean integrating
(either in series or in parallel) a plurality of photovoltaic cells
to form a photovoltaic module, where the cells/module can be formed
in a continuous fashion on a single film or substrate, e.g., a reel
to reel operation.
[0017] "Dianhydride" as used herein is intended to include
precursors or derivatives thereof, which may not technically be a
dianhydride but would nevertheless functionally equivalent due to
the capability of reacting with a diamine to form a polyamic acid
which in turn could be converted into a polyimide.
[0018] "Diamine" as used herein is intended to include precursors
or derivatives thereof, which may not technically be diamines but
are nevertheless functionally equivalent due to the capability of
reacting with a dianhydride to form a polyamic acid which in turn
could be converted into a polyimide.
[0019] "Polyamic acid" as used herein is intended to include any
polyimide precursor material derived from a combination of
dianhydride and diamine monomers or functional equivalents thereof
and capable of conversion to a polyimide.
[0020] "Sub-micron" is intended to describe particles having (as a
numerical average) at least one dimension that is less than a
micron.
[0021] "Chemical conversion" or "chemically converted" as used
herein denotes the use of a catalyst (accelerator) or dehydrating
agent (or both) to convert the polyamic acid to polyimide and is
intended to include a partially chemically converted polyimide
which is then dried at elevated temperatures to a solids level
greater than 98%.
[0022] "Aspect ratio" is intended to mean a ratio of one dimension
to another, such as a ratio of length to height.
[0023] In describing certain polymers it should be understood that
sometimes applicants are referring to the polymers by the monomers
used to make them or the amounts of the monomers used to make them.
While such a description may not include the specific nomenclature
used to describe the final polymer or may not contain
product-by-process terminology, any such reference to monomers and
amounts should be interpreted to mean that the polymer is made from
those monomers, unless the context indicates or implies
otherwise.
[0024] As used herein, the terms "comprises," "comprising,"
"includes," "including," "has," "having" or any other variation
thereof, are intended to cover a non-exclusive inclusion. For
example, a method, process, article, or apparatus that comprises a
list of elements is not necessarily limited to only those elements
but may include other elements not expressly listed or inherent to
such method, process, article, or apparatus. Further, unless
expressly stated to the contrary, "or" refers to an inclusive or
and not to an exclusive or. For example, a condition A or B is
satisfied by any one of the following: A is true (or present) and B
is false (or not present), A is false (or not present) and B is
true (or present), and both A and B are true (or present).
[0025] Also, articles "a" or "an" are employed to describe elements
and components of the disclosure. This is done merely for
convenience and to give a general sense of the disclosure. This
description should be read to include one or at least one and the
singular also includes the plural unless it is obvious that it is
meant otherwise.
Overview
[0026] The assemblies of the present disclosure have a polyimide
film and an electrode. The polyimide film serves as a support
(substrate) upon which an electrode is formed. The polyimide film
comprises a polyimide and a sub-micron filler. The polyimide has a
hybrid backbone structure comprising rigid rod portions and
non-rigid rod portions. The sub-micron filler can generally be
incorporated into polyimides of the present disclosure at
relatively high loadings without causing the polyimide film to be
unduly brittle while maintaining or decreasing coefficient of
thermal expansion and increasing storage modulus.
Polyimide
[0027] The polyimides of the present disclosure are derived from
the polymerization reaction of certain aromatic dianhydrides with
certain aromatic diamines to provide a polymeric backbone structure
that comprises both rigid rod portions and non-rigid rod portions.
The rigid rod portions arise from the polymerization of aromatic
rigid rod monomers into the polyimide, and the non-rigid rod
portions arise from the polymerization of non-rigid rod aromatic
monomers into the polyimide. Aromatic rigid rod monomers give a
co-linear (about 180.degree.) configuration to the polymer
backbone, and therefore relatively little movement capability, when
polymerized into a polyimide.
[0028] Examples of aromatic rigid rod diamine monomers are: [0029]
1,4-diaminobenzene (PPD), [0030] 4,4'-diaminobiphenyl, [0031]
2,2'-bis(trifluoromethyl) 4,4'-diaminobiphenyl (TFMB), [0032]
1,4-naphthalenediamine, [0033] 1,5-naphthalenediamine, [0034]
4,4''-diamino terphenyl, [0035] 4,4'-diamino benzanilide [0036]
4,4'-diaminophenyl benzoate, [0037]
3,3'-dimethyl-4,4'-diaminobiphenyl, [0038] 2,5-diaminotoluene, and
[0039] the like.
[0040] Examples of aromatic rigid rod dianhydride monomers are:
[0041] pyromellitic dianhydride (PMDA), [0042]
2,3,6,7-Naphthalenetetracarboxylic dianhydride, and [0043]
3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA).
[0044] Monomers having a freedom of rotational movement or bending
(once polymerized into a polyimide) substantially equal to or less
than the above examples (of rigid rod diamines and rigid rod
dianhydrides) are intended to be deemed rigid rod monomers for
purposes of this disclosure.
[0045] Non-rigid rod monomers for purposes of this disclosure are
intended to mean aromatic monomers capable of polymerizing into a
polyimide backbone structure having substantially greater freedom
of movement compared to the rigid rod monomers described and
exemplified above. The non rigid rod monomers, when polymerized
into a polyimide, provide a backbone structure having a bend or
otherwise are not co-linear along the polyimide backbone they
create (e.g., are not about 180.degree.). Examples of non-rigid rod
monomers in accordance with the present disclosure include any
diamine and any dianhydride capable of providing a rotational or
bending bridging group along the polyimide backbone. Examples of
rotational or bending bridging groups include --O--, --S--,
--SO.sub.2--, --C(O)--, --C(CH.sub.3).sub.2--,
--C(CF.sub.3).sub.2--, and --C(R,R')-- where R and R' are the same
or different and are any organic group capable of bonding to a
carbon.
[0046] Examples of non-rigid rod diamines include:
4,4'-diaminodiphenyl ether ("ODA"), 2,2-bis-(4-aminophenyl)propane,
1,3-diaminobenzene (MPD), 4,4'-diaminobenzophenone,
4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide,
4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone,
bis-(4-(4-aminophenoxy)phenyl sulfone (BAPS),
4,4'-bis-(aminophenoxy)biphenyl (BAPB), 3,4'-diaminodiphenyl ether,
4,4'-diaminobenzophenone, 4,4'-isopropylidenedianiline,
2,2'-bis-(3-aminophenyl)propane,
N,N-bis-(4-aminophenyl)-n-butylamine,
N,N-bis-(4-aminophenyl)methylamine, m-amino benzoyl-p-amino
anilide, 4-aminophenyl-3-aminobenzoate,
N,N-bis-(4-aminophenyl)aniline, 2,4-diaminotoluene,
2,6-diaminotoluene, 2,4-diamine-5-chlorotoluene,
2,4-diamino-6-chlorotoluene, 2,4-bis-(beta-amino-t-butyl)toluene,
bis-(p-beta-amino-t-butyl phenyl)ether,
p-bis-2-(2-methyl-4-aminopentyl)benzene, m-xylylene diamine,
p-xylylene diamine. 1,2-bis-(4-aminophenoxy)benzene,
1,3-bis-(4-aminophenoxy)benzene, 1,2-bis-(3-aminophenoxy)benzene,
1,3-bis-(3-aminophenoxy)benzene,
1-(4-aminophenoxy)-3-(3-aminophenoxy)benzene,
1,4-bis-(4-aminophenoxy)benzene, 1,4-bis-(3-aminophenoxy)benzene,
1-(4-aminophenoxy)-4-(3-aminophenoxy)benzene,
2,2-bis-(4-[4-aminophenoxy]phenyl)propane (BAPP),
2,2'-bis-(4-aminophenyl)-hexafluoro propane (6F diamine),
2,2'-bis-(4-phenoxy aniline) isopropylidene,
4,4'-diamino-2,2'-trifluoromethyl diphenyloxide,
3,3'-diamino-5,5'-trifluoromethyl diphenyloxide,
4,4'-trifluoromethyl-2,2'-diaminobiphenyl,
2,4,6-trimethyl-1,3-diaminobenzene,
4,4'-oxy-bis-[2-trifluoromethyl)benzene amine](1,2,4-OBABTF),
4,4'-oxy-bis-[3-trifluoromethyl)benzene amine],
4,4'-thio-bis-[(2-trifluoromethyl)benzene-amine],
4,4'-thiobis[(3-trifluoromethyl)benzene amine],
4,4'-sulfoxyl-bis-[(2-trifluoromethyl)benzene amine,
4,4'-sulfoxy]-bis-[(3-trifluoromethyl)benzene amine], and
4,4'-keto-bis-[(2-trifluoromethyl)benzene amine].
[0047] Examples of non-rigid rod aromatic dianhydrides include
2,2',3,3'-benzophenone tetracarboxylic dianhydride,
2,3,3',4'-benzophenone tetracarboxylic dianhydride,
3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA),
2,2',3,3'-biphenyl tetracarboxylic dianhydride, 2,3,3',4'-biphenyl
tetracarboxylic dianhydride, 4,4'-thio-diphthalic anhydride,
bis(3,4-dicarboxyphenyl)sulfone dianhydride (DSDA),
bis(3,4-dicarboxyphenyl) sulfoxide dianhydride, 4,4'-oxydiphthalic
anhydride (ODPA), bis(3,4-dicarboxyphenyl) thio ether dianhydride,
2,2-Bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA),
2,2-bis-(3,4-dicarboxyphenyl) 1,1,1,3,3,3,-hexafluoropropane
dianhydride (6FDA),
5,5-[2,2,2]-trifluoro-1-(trifluoromethyl)ethylidene,
bis-1,3-isobenzofurandione, bis (3,4-dicarboxyphenyl)methane
dianhydride, cyclopentadienyl tetracarboxylic acid dianhydride,
ethylene tetracarboxylic acid dianhydride,
2,2-bis(3,4-dicarboxyphenyl) propane dianhydride.
[0048] In some embodiments, the mole ratio of dianhydride to
diamine is 48-52:52-48 and the ratio of X:Y is 20-80:80-20 where X
is the mole percent of rigid rod dianhydride and rigid rod diamine,
and Y is the mole percent of non-rigid rod dianhydride and
non-rigid rod diamine based upon the total dianhydride component
and diamine component of the polyimide. An alternative embodiment,
the mole ratio of the dianhydride to diamine, can be any sub-range
within that broad ratio (e.g., 20-80 includes any range between and
optionally including 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75
and 80, and 80-20 includes any range between and optionally
including 80, 75, 70, 65, 60, 55, 45, 40, 35, 30, and 25).
[0049] In one embodiment, the polyimide of the present disclosure
is derived from substantially equal molar amounts of
4,4'-diaminodiphenyl ether (4,4'-ODA) non-rigid rod monomer, and
pyromellitic dianhydride (PMDA), rigid rod monomer. In another
embodiment, at least 70 mole percent of the aromatic dianhydride
component is pyromellitic dianhydride; and at least 70 mole percent
of the aromatic diamine component is 4,4'-diaminodiphenyl ether. In
some embodiments, at least 70, 75, 80, 85, 90 or 95 mole percent of
the aromatic dianhydride component is pyromellitic dianhydride
(based upon total dianhydride content of the polyimide); and at
least 70, 75, 80, 85, 90 or 95 mole percent of the aromatic diamine
component is 4,4'-diaminodiphenyl ether (based upon total diamine
content of the polyimide). Such PMDA//4,4'ODA polyimides have been
found to be particularly well suited for combination with the
sub-micron fillers of the present disclosure, for improved
properties at a relatively low cost. In another embodiment, the
polyimide is derived from 100 mole percent pyromellitic dianhydride
and 100 mole percent 4,4'-diaminodiphenyl ether. In another
embodiment, the polyimide is a random copolymer derived from
4,4'-diaminodiphenyl ether and 1,4 diaminobenzene with pyromellitic
dianhydride and 3,3',4,4'-biphenyl tetracarboxylic dianhydride. In
yet another embodiment, the polyimide is a random copolymer derived
from 4,4'-diaminodiphenyl ether and 1,4 diaminobenzene with
pyromellitic dianhydride.
[0050] In another embodiment, at least 75 mole percent of the
aromatic dianhydride component is pyromellitic dianhydride and 70
mole percent 4,4'-diaminodiphenyl ether and 30 mole percent 1,4
diaminobenzene as the aromatic diamine component.
[0051] In another embodiment, the polyimide is a block copolymer. A
block copolymer is a polymer in which there are sequences of
substantially one dianhydride/diamine combination along the polymer
backbone as opposed to a completely random distribution of monomer
sequences. Typically this is achieved by sequential addition of
different monomers during the polyamic acid preparation.
[0052] In yet another embodiment, the polyimide is block copolymer
derived from 4,4'-diaminodiphenyl ether and 1,4-diaminobenzene with
pyromellitic dianhydride. In yet another embodiment, the polyimide
is a block copolymer is derived from 4,4'-diaminodiphenyl ether
(4,4'-ODA) and 1,4-diaminobenzene (PPD) with pyromellitic
dianhydride (PMDA) and 3,3',4,4'-biphenyl tetracarboxylic
dianhydride (BPDA). In yet another embodiment, the polyimide is a
block copolymer consisting of substantially rigid blocks (PMDA
reacted with PPD) and substantially more flexible blocks (PMDA
reacted with ODA). In another embodiment, the block copolymer is
derived from 10 to 40 mole percent blocks of pyromellitic
dianhydride and 1,4-diaminobenzene and from 90 to 60 mole percent
blocks of pyromellitic dianhydride and 4,4'-diaminodiphenyl
ether.
Sub-Micron Filler
[0053] In accordance with the present disclosure, the filler is a
sub-micron (in at least one dimension) filler or a mixture of
sub-micron fillers.
[0054] In one embodiment, the polyimide film of the present
disclosure comprises at least one sub-micron filler, the sub-micron
filler: [0055] 1 being less than 550 nanometers (and in some
embodiments, less than 475, 450, 425, 400, 375, 350, 325, 300, 275,
250, 225, or 200 nanometers) in at least one dimension (since
fillers can have a variety of shapes in any dimension and since
filler shape can vary along any dimension, the "at least one
dimension" is intended to be a numerical average along that
dimension); [0056] 2. having an average aspect ratio greater than
3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 to 1; [0057] 3.
being less than 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45,
40, 35, 30, 25, 20, 15 or 10 percent of the polyimide film
thickness in all dimensions; and [0058] 4. being present in an
amount between and optionally including any two of the following
percentages: 10, 15, 20, 25, 30, 35, 40 and 45 volume percent of
the polyimide film.
[0059] Suitable sub-micron fillers are generally stable at
temperatures above 300, 350, 400, 425 or 450.degree. C., and in
some embodiments do not significantly decrease the electrical
insulation properties of the polyimide film. In some embodiments,
the sub-micron filler is selected from a group consisting of
needle-like fillers (acicular), fibrous fillers, platelet fillers
and mixtures thereof.
[0060] In one embodiment, the sub-micron filler is substantially
non-aggregated. The sub-micron filler can be hollow, porous, or
solid.
[0061] In one embodiment, the sub-micron filler of the present
disclosure exhibits an aspect ratio of at least 3, 4, 5, 6, 7, 8,
9, 10, 11, 12, 13, 14, or 15 to 1. In one embodiment, the
sub-micron filler aspect ratio is 5:1 or greater. In another
embodiment, the sub-micron filler aspect ratio is 10:1 or greater,
and in another embodiment, the aspect ratio is 12:1 or greater. In
some embodiments, a mixture of sub-micron fillers having aspect
ratio of at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 to
1 may be used. In some embodiments, the sub-micron filler is
selected from a group consisting of oxides (e.g., oxides comprising
silicon, magnesium and/or aluminum), nitrides (e.g., nitrides
comprising boron and/or silicon), carbides (e.g., carbides
comprising tungsten and/or silicon) and combinations thereof. In
some embodiments, the sub-micron filler is acicular titanium
dioxide, talc, SiC fiber, platy Al.sub.2O.sub.3 or mixtures
thereof. In some embodiments, the sub-micron filler is less than
(as a numerical average) 50, 25, 20, 15, 12, 10, 8, 6, 5, 4, or 2
microns in all dimensions.
[0062] In yet another embodiment, carbon fiber and graphite can be
used in combination with other sub-micron fillers to increase
mechanical properties. However in one embodiment, the loading of
graphite, carbon fiber and/or electrically conductive fillers may
need to be below the percolation threshold (perhaps less than 10
volume percent), since graphite and carbon fiber fillers can
diminish electrical insulation properties and in some embodiments,
diminished electrical insulation properties are not desirable.
[0063] In some embodiments, the sub-micron filler is coated with a
coupling agent. In some embodiments, the sub-micron filler is
coated with an aminosilane coupling agent. In some embodiments, the
sub-micron filler is coated with a dispersant. In some embodiments,
the sub-micron filler is coated with a combination of a coupling
agent and a dispersant. In some embodiments, the sub-micron filer
is coated with a coupling agent, a dispersant or a combination
thereof. Alternatively, the coupling agent and/or dispersant can be
incorporated directly into the polyimide film and not necessarily
coated onto the sub-micron filler. In some embodiments, the
sub-micron filler comprises a acicular titanium dioxide, at least a
portion of which is coated with an aluminum oxide.
[0064] In some embodiments, the sub-micron filler is chosen so that
it does not itself degrade or produce off-gasses at the desired
processing temperatures. Likewise in some embodiments, the
sub-micron filler is chosen so that it does not contribute to
degradation of the polymer.
[0065] In one embodiment, filler composites (e.g. single or
multiple core/shell structures) can be used, in which one oxide
encapsulates another oxide in one particle.
Polyimide Film
[0066] It has been discovered that relatively less expensive
polyimides can be filled with sub-micron filler of the present
disclosure and thereby perform, at least in some ways, more
similarly to more expensive polyimides, but at a much lower cost.
More expensive monomers such as BPDA or fluorinated monomers can at
least in part (or entirely) be replaced with less expensive
monomers. In addition to expensive monomers, some polyimides are
more difficult to process commercially, such as BPDA//PPD due to
blistering. Lower production rates drive up the cost of the film.
Additionally, polyimides derived from all rigid rod monomers may
have low CTE and high modulus but, when filled, have low
elongation. It has been found that the submicron fillers that have
an aspect ratio of 3:1 or greater can be incorporated at relatively
high loading levels (10 to 45 volume percent) into less expensive,
easily processable polyimides. The sub-micron filler of the present
disclosure tends to increase the storage modulus and decrease or
approximately maintain the CTE of the polyimide film of the present
disclosure with out causing the polyimide film to become unduly
brittle.
[0067] It is surprising that the sub-micron filler of the present
disclosure may not behave in the same manner in all polyimides.
Surprisingly in a rigid rod polyimide (BPDA//PPD) the CTE may be
greater than in unfilled rigid rod polyimide.
[0068] The sub-micron filler of the present disclosure, when
incorporated into the polyimides of the present disclosure, produce
polyimide films having better properties (or balance of properties)
compared to their conventional non-high aspect ratio (less than 3:1
aspect ratio) counterparts.
[0069] In some embodiments, the polyimide film comprises a
polyimide derived from 100 mole percent of pyromellitic dianhydride
as the aromatic dianhydride component; and 100 mole percent
4,4'-diaminodiphenyl ether as the aromatic diamine component and
the sub-micron filler is acicular Titanium dioxide, talc or mixture
thereof. In some embodiments, the polyimide is a homopolymer of
pyromellitic dianhydride and 4,4'-diaminodiphenyl ether.
[0070] In another embodiment, the polyimide film comprises a
polyimide wherein the polyimide is block copolymer derived from: 10
to 40 mole % blocks of pyromellitic dianhydride and 1,4
diaminobenzene; from 90 to 60 mole % blocks of pyromellitic
dianhydride and 4,4'-diaminodiphenyl ether and the sub-micron
filler is acicular Titanium dioxide, talc or mixture thereof.
[0071] The above described polyimide film of the present disclosure
is well suited for use as a photovoltaic device substrate. The
properties of the polyimide film of the present disclosure are well
adapted for use in a roll-to-roll process, in which deposition of
additional layers in the manufacture of photovoltaic cells can be
effected on a continuous web of the polyimide film. By "roll to
roll" it is meant that the process be fed with a roll of flexible
substrate (polyimide film) and that the process comprise a take up
roll around which is wound the completed (or substantially
completed) flexible solar cell. The invention contemplates that the
flexible substrate (polyimide film) may travel in both directions
in the roll to roll configuration.
Thermal and Dimensional Stability
[0072] While it is generally known that the addition of filler will
decrease CTE and increase storage modulus, it is surprising, that
for the sub-micron fillers of the present disclosure, there is a
threshold above which a significant increase in storage modulus
and/or a decrease in CTE is observed. In one embodiment, the
sub-micron filler will substantially maintain (within 80, 70. 60,
50, 40, 30, 20, 10, 5, 4, 3, 2, or 1 percent, plus or minus) the
coefficient of thermal expansion (CTE) while improving mechanical
and thermal properties.
[0073] In one embodiment, the polyimide films of the present
disclosure have an in-plane CTE in a range between (and optionally
including) any two of the following: 1, 5, 10, 15, 20, 25, 30 and
35 ppm/.degree. C., where the in-plane coefficient of thermal
expansion (CTE) is measured between 60.degree. C. (or 50.degree.
C.) and 350.degree. C.
[0074] Some unfilled block or random copolymers of the present
disclosure can have a relatively low CTE. Thus, in some
embodiments, sub-micron fillers of the present disclosure have
little impact on a block copolymer CTE. In some embodiments, the
sub-micron fillers of the present disclosure may increase the CTE
of block or random copolymers having a low CTE but the CTE is still
maintained in a desirable range.
[0075] The thickness of a polyimide film can also impact CTE, where
thinner films tend to give a lower CTE (and thicker films, a higher
CTE), and therefore, film thickness can be used to fine tune
polyimide film CTE, depending upon any particular application
selected. The polyimide film of the present disclosure has a
thickness in a range between (and optionally including) any of the
following thicknesses (in microns): 5, 6, 8, 10, 12, 15, 20, 25,
50, 75, 100, 125 and 150 microns. Monomers and sub-micron fillers
within the scope of the present disclosure can also be selected or
optimized to fine tune CTE within the above range. Ordinary skill
and experimentation may be necessary in fine tuning any particular
CTE of the polyimide film of the present disclosure, depending upon
the particular application. In some embodiments, the in-plane CTE
of the polyimide film can be obtained by thermomechanical analysis
utilizing a TA Instruments TMA-2940 run at 10.degree. C./min, up to
400.degree. C., then cooled and reheated to 400.degree. C., with
the CTE in ppm/.degree. C. obtained during the reheat scan between
50.degree. C. and 350.degree. C. In another embodiment, the
in-plane CTE of the film can be obtained by Thermal Mechanical
Analysis (TA Instruments, TMA-2940, heat 10.degree. C./min, up to
460.degree. C., then cooled and reheat to 500.degree. C.) was
evaluated between 50-350.degree. C. on the reheat. In another
embodiment, the in-plane CTE of the film can be obtained by Thermal
Mechanical Analysis (TA Instruments, TMA-2940, heat 10.degree.
C./min, up to 380.degree. C., then cooled and reheated to
380.degree. C.) and evaluated between 50-350.degree. C. on the
reheat.
[0076] In some embodiments, the sub-micron filler increases the
storage modulus above the glass transition temperature (Tg) of the
polyimide. In some embodiments, the sub-micron filler of the
present disclosure increases the storage modulus at 25.degree. C.
at least 20, 22, 24, 26, 28 or 30% compared to sub-micron filler
having an aspect ratio less than 3:1. In some embodiments, the
sub-micron filler of the present disclosure increases the storage
modulus at 480.degree. C. to 500.degree. C. at least 40, 42, 44 or
46% compared to sub-micron filler having an aspect ration less than
3:1. In some embodiments, the sub-micron filler of the present
disclosure increases the storage modulus at 25.degree. C. at least
38, 40, 42, 44 or 46% compared to unfilled polyimide. In some
embodiments, the sub-micron filler of the present disclosure
increases the storage modulus at 480.degree. C. to 500.degree. C.
at least 52, 53, 54 or 55% compared to unfilled polyimide.
[0077] Typically, as the amount of filler increases in a film, the
more brittle and difficult to process the film tends to become.
Typically when tensile elongation is less than 20 percent, films
are difficult to process, thus, are of limited commercial value. It
is surprising that when the sub-micron fillers of the present
disclosure are added to a polyimide having a mole ratio of
dianhydride to diamine of 48-52:52-48 and the ratio of X:Y is
20-80:80-20 where X is the mole percent of rigid rod dianhydride
and rigid rod diamine, and Y is the mole percent of non-rigid rod
dianhydride and non-rigid rod diamine, the tensile elongation
remains acceptable. In some embodiments, the tensile elongation
remains acceptable when greater than 10 volume percent of the
sub-micron filler is used. In some embodiments, the tensile
elongation remains acceptable when greater than 30 volume percent
of the sub-micron filler is used. In another embodiment, the
tensile elongation remains acceptable when greater than 40 volume
percent of the sub-micron filler is used.
[0078] Generally, when forming the polyimide, a chemical conversion
process (as opposed to a thermal conversion process) will provide a
lower CTE polyimide film. Thus, while the advantages of the present
disclosure can be seen for both chemically or thermally converted
polyimides, the advantages of incorporating the sub-micron filler
of the present disclosure may be most useful for chemically
converted polyimides of the present disclosure.
Polyimide Film Formation
[0079] Polyimide films of the present disclosure can be made by
methods well known in the art. In some embodiments, the polyimide
film can be produced by combining the above monomers together with
a solvent to form a polyamic acid (also called a polyamide acid
solution). The dianhydride and diamine components are typically
combined in a molar ratio of aromatic dianhydride component to
aromatic diamine component of from 0.90 to 1.10. Molecular weight
can be adjusted by adjusting the molar ratio of the dianhydride and
diamine components.
[0080] Chemical or thermal conversion can be used in the practice
of the present disclosure. In instances where chemical conversion
is used, a polyamic acid casting solution is derived from the
polyamic acid solution. In one embodiment, the polyamic acid
casting solution comprises the polyamic acid solution combined with
conversion chemicals, such as: (i) one or more dehydrating agents,
such as, aliphatic acid anhydrides (acetic anhydride, etc.) and
aromatic acid anhydrides; or (ii) one or more catalysts, such as,
aliphatic tertiary amines (triethylamine, etc.), aromatic tertiary
amines (dimethylaniline, etc) and heterocyclic tertiary amines
(pyridine, picoline, isoquinoline, etc). The anhydride dehydrating
material is often used in a molar excess of the amount of amide
acid groups in the copolyamic acid. The amount of acetic anhydride
used is typically about 2.0-3.0 moles per equivalent of amide acid.
Generally, a comparable amount of tertiary amine catalyst is
used.
[0081] In one embodiment, the polyamic acid is dissolved in an
organic solvent at a concentration from about 5 weight percent up
to and including 40 weight percent. In one embodiment, the polyamic
acid is dissolved in an organic solvent at a concentration of about
5, 10, 15, 20, 25, 30, 35 or 40 weight percent. Examples of
suitable solvents include: formamide solvents
(N,N-dimethylformamide, N,N-diethylformamide, etc.), acetamide
solvents (N,N-dimethylacetamide, N,N-diethylacetamide, etc.),
pyrrolidone solvents (N-methyl-2-pyrrolidone,
N-vinyl-2-pyrrolidone, etc.), phenol solvents (phenol, o-, m- or
p-cresol, xylenol, halogenated phenols, catechol, etc.),
hexamethylphosphoramide and gamma-butyrolactone. It is desirable to
use one of these solvents or mixtures thereof. It is also possible
to use combinations of these solvents with aromatic hydrocarbons
such as xylene and toluene, or ether containing solvents like
diglyme, propylene glycol methyl ether, propylene glycol, methyl
ether acetate, tetrahydrofuran, and the like.
[0082] In one embodiment, the prepolymer can be prepared and
combined with the sub-micron filler (dispersion or colloid thereof)
using numerous variations to form the polyimide film of this
disclosure. "Prepolymer" is intended to mean a lower molecular
weight polymer, typically made with a slight stoichiometric excess
(about 2-4%) of diamine monomer (or excess dianhydride monomer).
Increasing the molecular weight (and solution viscosity) of the
prepolymer can be accomplished by adding incremental amounts of
additional dianhydride (or additional diamine, in the case where
the dianhydride monomer is originally in excess in the prepolymer)
in order to approach a 1:1 stoichiometric ratio of dianhydride to
diamine.
[0083] Useful methods for producing prepolymer in accordance with
the present disclosure can be found in U.S. Pat. No. 5,166,308 to
Kreuz, et al. Numerous variations are also possible, such as: (a) a
method wherein the diamine components and dianhydride components
are preliminarily mixed together and then the mixture is added in
portions to a solvent while stirring, (b) a method wherein a
solvent is added to a stirring mixture of diamine and dianhydride
components (contrary to (a) above), (c) a method wherein diamines
are exclusively dissolved in a solvent and then dianhydrides are
added thereto at such a ratio as allowing to control the reaction
rate, (d) a method wherein the dianhydride components are
exclusively dissolved in a solvent and then amine components are
added thereto at such a ratio to allow control of the reaction
rate, (e) a method wherein the diamine components and the
dianhydride components are separately dissolved in solvents and
then these solutions are mixed in a reactor, (f) a method wherein
the polyamic acid with excessive amine component and another
polyamic acid with excessive dianhydride component are
preliminarily formed and then reacted with each other in a reactor,
particularly in such a way as to create a non-random or block
copolymer, (g) a method wherein a specific portion of the amine
components and the dianhydride components are first reacted and
then the residual diamine components are reacted, or vice versa,
(h) a method wherein the conversion chemicals are mixed with the
polyamic acid to form a polyamic acid casting solution and then
cast to form a gel film, (i) a method wherein the components are
added in part or in whole in any order to either part or whole of
the solvent, also where part or all of any component can be added
as a solution in part or all of the solvent, (j) a method of first
reacting one of the dianhydride components with one of the diamine
components giving a first polyamic acid, then reacting the other
dianhydride component with the other amine component to give a
second polyamic acid, and then combining the amic acids in any one
of a number of ways prior to film formation, and (k) a method of
creating block copolymers by sequential addition, e.g., adding a
first diamine and a first dianhydride to form a polyamic acid
having excess dianhydride (or excess diamine) to create a first
block and then adding a second diamine and a second dianhydride to
the polyamic acid to form a second block in the presence of the
first block; alternatively, blocks can be made based upon different
dianhydrides (and the same diamine) or based upon different
dianhydrides and different diamines (in each block), depending upon
the particular application or properties desired.
[0084] The sub-micron filler (dispersion or colloid thereof) can be
added at several points in the polyimide film preparation. In one
embodiment, the colloid or dispersion is incorporated into a
prepolymer to yield a Brookfield solution viscosity in the range of
about 50-100 poise at 25.degree. C. In an alternative embodiment,
the colloid or dispersion can be combined with the monomers
directly, and in this case, polymerization occurs with the
nanocolloid present during the reaction. The monomers may have an
excess of either monomer (diamine or dianhydride) during this "in
situ" polymerization. The monomers may also be added in a 1:1
ratio. In the case where the monomers are added with either the
amine (case i) or the dianhydride (case ii) in excess, increasing
the molecular weight (and solution viscosity) can be accomplished,
if necessary, by adding incremental amounts of additional
dianhydride (case i) or diamine (case ii) to approach the 1:1
stoichiometric ratio of dianhydride to amine.
[0085] The polyamic acid casting solution can then be cast or
applied onto a support, such as an endless belt or rotating drum.
The polyamic acid contain conversion chemical reactants. Next, the
solvent-containing film can be converted into a self-supporting
film by baking at an appropriate temperature (thermal curing) to
remove solvent or baking together with the chemical conversion
reactants (chemical curing). The film can then be separated from
the support, oriented such as by tentering, with continued thermal
curing to provide a polyimide film.
[0086] Generally speaking, film smoothness is desirable, since
surface roughness: i. can interfere with the functionality of the
layer or layers deposited on the polyimide film of the present
disclosure, ii. can increase the probability of electrical or
mechanical defects, and iii. can diminish property uniformity along
the polyimide film. In one embodiment, the sub-micron filler (and
any other discontinuous domains) are sufficiently dispersed during
polyimide film formation, such that the sub-micron filler (and any
other discontinuous domains) are sufficiently between the surfaces
of the polyimide film upon polyimide film formation to provide a
final polyimide film having an average surface roughness (Ra) of
less than 1000, 750, 500 or 400 nanometers. Surface roughness as
provided herein can be determined by optical surface profilometry
to provide Ra values, such as, by measuring on a Veeco Wyco NT 1000
Series instrument in VSI mode at 25.4.times. or 51.2.times.
utilizing Wyco Vision 32 software.
[0087] The polyamic acid (and casting solution) can further
comprise any one of a number of additives, such as processing aids
(e.g., oligomers), antioxidants, light stabilizers, flame retardant
additives, anti-static agents, heat stabilizers, ultraviolet
absorbing agents, fillers or various reinforcing agents.
[0088] An alkoxy silane coupling agent (or any conventional,
nonconventional, presently known or future discovered coupling
agent) can be added during the process by pretreating the
sub-micron filler prior to formulation. Alkoxysilane coupling
agents can also be added during the "in situ" polymerization by
combining the fillers and monomers with the alkoxysilane, generally
so long as the coupling agent does not interfere with the
polymerization reaction.
[0089] In some cases, the dianhydride can be contacted with the
sub-micron filler. While not intending to be bound to any
particular theory or hypothesis, it is believed such contact
between the dianhydride and the sub-micron filler can functionalize
the sub-micron filler with the dianhydride prior to further
reaction with the monomers or prepolymer. Ultimately, a filled
polyamic acid composition is generally cast into a film, which is
subjected to drying and curing (chemical and/or thermal curing) to
form a filled polyimide film. Any conventional or non-conventional
method of manufacturing filled polyimide films can be used in
accordance with the present disclosure. The manufacture of filled
polyimide films in general is well known and need not be further
described here. In one embodiment, the polyimide used in polyimide
film of the present disclosure has a high glass transition
temperature (Tg) of greater than 300, 310, 320, 330, 340, 350, 360,
370 380, 390 or 400.degree. C. A high Tg generally helps maintain
mechanical properties, such as storage modulus, at high
temperatures.
[0090] In some embodiments, electrically insulating fillers may be
added to modify the electrical properties of the polyimide film. In
some embodiments, it is important that the polyimide film be free
of pinholes or other defects (foreign particles, gels, filler
agglomerates or other contaminates) that could adversely impact the
electrical integrity and dielectric strength of the polyimide film,
and this can generally be addressed by filtering. Such filtering
can be done at any stage of the polyimide film manufacture, such
as, filtering solvated filler before or after it is added to one or
more monomers and/or filtering the polyamic acid, particularly when
the polyamic acid is at low viscosity, or otherwise, filtering at
any step in the manufacturing process that allows for filtering. In
one embodiment, such filtering is conducted at the minimum suitable
filter pore size or at a level just above the largest dimension of
the selected filler material. In some embodiments, the sub-micron
filler is subjected to intense dispersion energy, such as agitation
and/or high shear mixing or media milling or other dispersion
techniques, including the use of dispersing agents, when
incorporated into the film (or incorporated into a polyimide
precursor) to inhibit unwanted agglomeration above the desired
maximum filler size or to break up aggregates which may be
originally present in the sub-micron filler. As the aspect ratio of
the sub-micron filler increases, so too does the tendency of the
sub-micron filler's long axis to align or otherwise position itself
parallel to the outer surfaces of the film.
[0091] A single layer film can be made thicker in an attempt to
decrease the effect of defects caused by unwanted (or undesirably
large) discontinuous phase material within the film. Alternatively,
multiple layers of polyimide may be used to diminish the harm of
any particular defect (unwanted discontinuous phase material of a
size capable of harming desired properties) in any particular
layer, and generally speaking, such multilayers will have fewer
defects in performance compared to a single polyimide layer of the
same thickness. Using multiple layers of polyimide films can
diminish or eliminate the occurrence of defects that may span the
total thickness of the film, because the likelihood of having
defects that overlap in each of the individual layers tends to be
extremely small. Therefore, a defect in any one of the layers is
much less likely to cause an electrical or other type failure
through the entire thickness of the film. In some embodiments, the
polyimide film comprises two or more polyimide layers. In some
embodiments, the polyimide layers are the same. In some
embodiments, the polyimide layers are different. In some
embodiments, the polyimide layers independently may comprise a
thermally stable filler, reinforcing fabric, inorganic paper,
sheet, scrim or combinations thereof. Optionally, 0-55 weight
percent of the film also includes other ingredients to modify
properties as desired or required for any particular
application.
[0092] It would be desirable for the polyimide films used in the
assemblies of the present disclosure resist shrinkage or creep
(even under tension, such as, reel to reel processing) within a
broad temperature range, such as, from about room temperature to
temperatures in excess of 400.degree. C., 425.degree. C. or
450.degree. C. In one embodiment, the polyimide film changes in
dimension by less than 1, 0.75, 0.5, or 0.25 percent when subjected
to a temperature of 460.degree. C. for 30 minutes while under a
stress in a range from 7.4-8.0 MPa (megapascals). In some
embodiments, the polyimide films have sufficient dimensional and
thermal stability to be a viable alternative to metal or ceramic
support materials. In some embodiments, the polyimide film has
improved adherence to the electrode.
Assembly
[0093] Assemblies of the present disclosure comprise an electrode
and a polyimide film as described above. The assemblies are
particularly useful in thin film photovoltaic cells (solar cells).
Thus, in some embodiments, assembly of the present disclosure
further comprises a light absorber layer where the electrode is
between the light absorber layer and the polyimide film, and the
electrode is in electrical communication with the light absorber
layer. The light absorber layer is a semiconductive material
(semiconductor). In some embodiments, the light absorber layer is
amorphous silicon or microcrystalline silicon. In another
embodiment, the light absorber layer is a CIGS/CIS light absorber
layer. "CIGS/CIS" is intended to mean i. a copper indium gallium
di-selenide composition; ii. a copper indium gallium disulfide
composition; iii. a copper indium di-selenide composition; iv. a
copper indium disulfide composition; or v. any element or
combination of elements that could be substituted for copper,
indium, gallium, di-selenide, and/or disulfide, whether presently
known or developed in the future. In yet another embodiment, the
light absorber layer is II-VI ternary alloy semiconductors (CdZnTe,
HgCdTe, HgZnTe, HgZnSe). In yet another embodiment, the light
absorber layer is CuZnSnS.sub.4 or CuZnSnSe.sub.4. Additional
useful light absorber layers are, but not limited to: [0094] 1.
Group IV compound semiconductors (SiGe, SiC); [0095] 2. Group III-V
semiconductors (AlSb, AlAs, AlN, AlP, BN, BP, BAs, GaSb, GaAs, GaN,
GaP, InSb, InAs, InN, InP); [0096] 3. Group III-V semiconductor
alloys (AlGaAs, InGaAs, InGaP, AlInAs, AlInAs, AlInSb, GaAsN,
GaAsP, AlGaN, AlGaP, InGaN, InAsSb, InGaSb); [0097] 4. III-V
quaternary semiconductor alloys (AlGaInP, AlGaAsP, InGaAsP,
InGaAsP, AlInAsP, AlGaAsN, InGaAsN, InAlAsN, GaAsSbN); [0098] 5.
III-V quinary semiconductor alloys (GaInNAsSb, GaInAsSbP): [0099]
6. II-VI semiconductors (CdSe, CdS, CdTe, ZnO, ZnSe, ZnS, ZnTe);
[0100] 7. I-VII semiconductors (CuCl); [0101] 8. IV-VI
semiconductors (PbSe, PbS, PbTe, SnS, SnTe); [0102] 9. IV-VI
ternary semiconductors (PbSnTe, TI.sub.2SnTe.sub.5,
TI.sub.2GeTe.sub.5); [0103] 10. V-VI semiconductors
(Bi.sub.2Te.sub.3); [0104] 11. II-V semiconductors
(Cd.sub.3P.sub.2, Cd.sub.3As.sub.2, Cd.sub.3Sb.sub.2,
Zn.sub.3P.sub.2, Zn.sub.3As.sub.2, Zn.sub.3Sb.sub.2); [0105] 12.
layered semiconductors (PbI.sub.2, MoS.sub.2, GaSe, SnS,
Bi.sub.2S.sub.3).sub.; [0106] 13. others (PtSi, BiI.sub.3,
HgI.sub.2, TIBr); [0107] 14. and the like.
[0108] The electrode metals are typically deposited by sputtering.
In some embodiments, the electrode is flexible. The light absorber
layer can be deposited by sputtering or other physical vapor
deposition (PVD) methods known in the art for this purpose, such as
close space sublimation (CSS), vapor transport deposition (VTD),
evaporation, close-space vapor transport (CSVT) or similar PVD
method or by chemical vapor deposition (CVD) methods. In one
embodiment the light absorber layer can be deposited, typically at
temperatures of about 400.degree. C. This is particularly
advantages for CIGS systems, where a high temperature
deposition/annealing step is generally applied to improve light
absorber layer performance. In some embodiments, the polyimide film
can also be coated on both sides with the electrode metal even if
only one metal side is used as the electrode on which the light
absorber layer is deposited.
[0109] The polyimide film can be reinforced with thermally stable,
inorganic: fabric, paper (e.g., mica paper), sheet, scrim or
combinations thereof. In some embodiments, the polyimide film of
the present disclosure has adequate electrical insulation
properties to allow multiple CIGS/CIS photovoltaic cells to be
monolithically integrated into a photovoltaic module. In some
embodiments, the assembly further comprises a plurality of
monolithically integrated CIGS/CIS photovoltaic cells. In some
embodiments, the polyimide films of the present disclosure provide:
[0110] i. low surface roughness, i.e., an average surface roughness
(Ra) of less than 400, 350, 300, 275 or 100 nanometers; [0111] ii.
low levels of surface defects; and/or [0112] iii. other useful
surface morphology, to diminish or inhibit unwanted defects, such
as, electrical shorts.
[0113] The polyimide films used in the assemblies of the present
disclosure should have high thermal stability so the films do not
substantially degrade, lose weight, have diminished mechanical
properties, or give off significant volatiles, e.g., during the
light absorber layer deposition and/or annealing process in a
CIGS/CIS application of the present disclosure. In a CIGS/CIS
application, in one embodiment the polyimide film should be thin
enough to not add excessive weight to the photovoltaic module, but
thick enough to provide high electrical insulation at operating
voltages, which in some cases may reach 400, 500, 750 or 1000 volts
or more.
[0114] The polyimide films used in the assemblies of the present
disclosure should have good adhesion to the electrode. In some
embodiments, polyimide films used in the assemblies of the present
disclosure a low CTE can be obtained to more closely match those of
the semiconductor layer deposited thereon. In some embodiments, the
filler increases the storage modulus above the glass transition
temperature (Tg) of the polyimide film. The addition of filler
typically allows for the retention of mechanical properties at high
temperatures and can improve handling characteristics. In some
embodiments, the crystallinity and amount of crosslinking of the
polyimide film can aid in storage modulus retention.
[0115] In some embodiments, the polyimide film used in an assembly
of the present disclosure has an isothermal weight loss of less
than 2, 1.5, 1, 0.75, 0.5 or 0.3 percent at 500.degree. C. over
about 30 minutes in an inert environment, such as, in a vacuum or
under nitrogen or other inert gas. Polyimides used in the
assemblies of the present disclosure have high dielectric strength,
generally higher than many common inorganic insulators. In some
embodiments, polyimides used in the assemblies of the present
disclosure have a breakdown voltage equal to or greater than 10
V/micrometer.
[0116] In some embodiment, there is an interface layer between the
electrode and light absorber layer. Interface layer materials are
known in the art and any suitable material such as ZnTe or similar
materials that provide advantages in contacting absorber materials
such as CdTe and/or CIGS which do not easily form ohmic contacts
directly with metals. The interface layer can be deposited by
sputtering or by evaporation.
[0117] In some embodiments, following deposition of the light
absorber layer, a window layer can be deposited on the light
absorber layer by PVD methods. In one embodiment, the window
layer(s) may comprise CdS, ZnS, CdZnS, ZnSe, In.sub.2S.sub.3,
and/or any conventional or nonconventional, known or future
discovered window layer material. In one embodiment CdS is the
window layer material and may be deposited by those techniques
known in the art such as CSS or VTD.
[0118] In some embodiments, a transparent conductive oxide (TCO) is
deposited on the window layer. The TCO can be deposited by PVD
methods, for example sputtering. Common TCO's known in the art for
this purpose include ZnO, ZnO:Al, ITO, SnO.sub.2 and CdSnO.sub.4.
ITO is In.sub.2O.sub.3 containing 10% of Sn. In some embodiments,
the TCO thickness is about 200 nm to 2,000 nm, preferably about 500
nm.
[0119] The present disclosure contemplates the deposition of
additional layers if desired. Non-limiting examples include a top
metal contact in a grid-like pattern for improved solar cell device
performance and an encapsulating or protective material such as,
but not limited to, ethylene vinyl acetate (EVA) or Tedlar.RTM..
Once completed, the flexible solar cell can be re-rolled onto a
take-up spool. This method is either semi-continuous or
continuous.
[0120] Referring now to FIG. 1, an embodiment of the present
disclosure is illustrated as a thin-film solar cell, indicated
generally at 10. The thin-film solar cell 10 includes a flexible
polyimide film 12 containing sub-micron filler as described and
discussed above. A bottom electrode 16 (comprising molybdenum, for
example) is applied onto the flexible polyimide film 12, such as,
by sputtering, evaporation deposition or the like. A semiconductor
light absorber layer 14 (comprising Cu(In, Ga)Se.sub.2, for
example) is deposited over the bottom electrode 16. The deposition
of the semiconductor light absorber layer 14 onto the bottom
electrode 16 and the flexible polyimide film 12 can be by any of a
variety of conventional or non-conventional techniques including,
but not limited to, casting, laminating, co evaporation,
sputtering, physical vapor deposition, chemical vapor deposition,
and the like. Deposition processes for semiconductor light absorber
layer 14 are well known and need not be further described here
(examples of such deposition processes are discussed and described
in U.S. Pat. No. 5,436,204 and U.S. Pat. No. 5,441,897).
[0121] An optional adhesion layer or adhesion promoter (not shown)
can be used to increase adhesion between any of the above described
layers. In one embodiment, the flexible polyimide film 12 is thin
and flexible, i.e., approximately 8 microns to approximately 150
microns, in order that the thin-film solar cell 10 is lightweight,
or the flexible polyimide film (substrate) 12 can be thick and
rigid to improve handling of the thin-film solar cell 10.
[0122] To complete the construction of the thin-film solar cell 10
in this particular embodiment, additional optional layers can be
applied. For example, the CIGS light absorber layer 14 can be
paired (e.g., covered) with a II/VI film 22 to form a photoactive
heterojunction. In some embodiments, the II/VI film 22 is
constructed from cadmium sulfide (CdS). Alternatively, the II/VI
films 22 can be constructed from other materials including, but not
limited to, cadmium zinc sulfide (CdZnS) and/or zinc selenide
(ZnSe) is also within the scope of the present disclosure.
[0123] A transparent conducting oxide (TCO) layer 23 for collection
of current is applied to the II/VI film. Preferably, the
transparent conducting oxide layer 23 is constructed from zinc
oxide (ZnO), although constructing the transparent conducting oxide
("TCO") layer 23 from other materials is also within the scope of
the present disclosure.
[0124] A suitable grid contact 24 or other suitable collector is
deposited on the upper surface of the TCO layer 23 when forming a
stand-alone thin-film solar cell 10. The grid contact 24 can be
formed from various materials but should have high electrical
conductivity and form a good ohmic contact with the underlying TCO
layer 23. In some embodiments, the grid contact 24 is constructed
from a metal material, although constructing the grid contact 24
from other materials including, but not limited to, aluminum,
indium, chromium, or molybdenum, with an additional conductive
metal overlayment, such as copper, silver, or nickel is within the
scope of the present disclosure.
[0125] In some embodiments, one or more anti-reflective coatings
(not shown) can be applied to the exposed surfaces of the grid
contact 24 and the exposed surfaces of transparent conducting oxide
layer 23 that are not in contact with the grid contacts. In another
embodiment, an anti-reflective coating can be applied to only the
exposed surfaces of transparent conducting oxide layer 23 that are
not in contact with the grid contacts. The anti-reflective coating
improves the collection of incident light by the thin-film solar
cell 10. As understood by a person skilled in the art, any suitable
anti-reflective coating is within the scope of the present
disclosure.
[0126] The invention will be further described in the following
examples, which are not intended to limit the scope of the
invention described in the claims.
EXAMPLES
[0127] The invention will be further described in the following
examples, which are not intended to limit the scope of the
invention described in the claims.
[0128] In all examples, for calculations to convert to composition
weight percentages to equivalent volume percentages, densities of
4.2 g/cc for the acicular titanium dioxide, 2.75 g/cc for talc,
3.22 g/cc for SiC and 1.42 g/cc for the polyimide were used.
[0129] Examples 1-4 demonstrate that the sub-micron filler of the
present disclosure at 10 volume percent or higher significantly
increase storage modulus and lower CTE when compared to unfilled
Comparative Example 1, while maintaining adequate elongation to
break.
Example 1
15 vol % (34.3 wt %) Acicular TiO.sub.2 in PMDA//ODA
[0130] 25.0 grams of acicular TiO.sub.2 (FTL-110, Ishihara
Corporation, USA) was combined with 141.11 grams of anhydrous DMAC.
This slurry was mixed at high shear for approximately 10 to 15
minutes using Silverson Model L4RT high-shear mixer (Silverson
Machines, LTD, Chesham Baucks, England) equipped with a
square-hole, high-shear screen (with a blade speed of approximately
4000 rpm).
[0131] In a round bottom flask, 74.1 grams of the slurry containing
acicular TiO.sub.2 was mixed with 116.94 grams of PMDA//ODA
prepolymer (20 wt % solution in anhydrous DMAC), and the resulting
mixture was stirred for approximately 24 hours. During this
operation, a gentle nitrogen gas purge was used in the round bottom
flask.
[0132] After stirring for approximately 24 hours, this material was
filtered through 45 micron filter media (Millipore, 45 micron
polypropylene screen, PP4504700).
[0133] In a separate container, a 6 wt % solution of pyromellitic
anhydride (PMDA) was prepared by combining 9.00 g of PMDA (Aldrich
412287, Allentown, Pa.) and 15 ml of DMAC.
[0134] The PMDA solution was slowly added to the prepolymer slurry
to achieve a final viscosity of 1090 poise. The formulation was
stored overnight at 0.degree. C. to allow it to degas.
[0135] The formulation was cast using a 25 mil doctor blade onto a
surface of a glass plate to form a 3''.times.4'' film. The cast
film and the glass plate are then soaked in a solution containing
110 ml of 3-picoline (beta picoline, Aldrich, 242845) and 110 ml of
acetic anhydride (Aldrich, 98%, P42053).
[0136] The film was subsequently lifted off of the glass surface,
and mounted on a 3''.times.4'' pin frame. The mounted film was
placed in a furnace (Thermolyne, F6000 box furnace). The furnace
was purged with nitrogen and heated according to the following
temperature protocol:
[0137] 40.degree. C. to 125.degree. C. (ramp at 4.degree.
C./min)
[0138] 125.degree. C. to 125.degree. C. (soak 30 min)
[0139] 125.degree. C. to 250.degree. C. (ramp at 4.degree.
C./min)
[0140] 250.degree. C. (soak 30 min)
[0141] 250.degree. C. to 400.degree. C. (ramp at 5.degree.
C./min)
[0142] 400.degree. C. (soak 20 min)
[0143] The coefficient of thermal expansion was measured by
thermomechanical analysis (TMA). A TA Instrument model 2940 was
used in tension mode. The instrument was purged with N.sub.2 gas at
30-50 ml/min. A mechanical cooler was also used, which allowed
temperature of the instrument to rapidly cool down between heating
cycles. The film was cut to a 2.0 mm width and 6-9 mm length (in MD
or casting direction). The film was clamped lengthwise to a length
of 7.5-9.0 mm. A preload tension was set for 5 grams of force. The
film was then subjected to heating from 0.degree. C. to 400.degree.
C. at 10.degree. C./min rate, held at 400.degree. C. for 3 minutes,
and cooled back down to 0.degree. C.
[0144] A second heating cycle to 400.degree. C. was performed in
the same way. The calculations of thermal expansion coefficient in
the unit of .mu.m/m-.degree. C. (or pp/.degree. C.) from 60.degree.
C. to 400.degree. C. were reported for the casting direction (MD)
for the second heating cycle.
[0145] Storage modulus (E') was measured by a Dynamic Mechanical
Analysis (DMA) instrument was used to characterize the mechanical
behavior of the film. The DMA operation was based on the
viscoelastic response of polymers subjected to a small oscillatory
strain (e.g., 10 .mu.m) as a function of temperature and time (TA
Instruments, New Castle, Del., USA, DMA 2980). The films were
placed under tension in a multifrequency-strain mode. A finite size
of rectangular specimen was clamped between stationary jaws and
movable jaws. The films were 6-6.4 mm in width, 0.03-0.05 mm thick
and 10 mm in length. The MD direction was used, and the film was
fastened with 3 in-lb torque force. The static force in the length
direction was 0.05 N with autotension of 125%. The film was heated
at frequency of 1 Hz from 0.degree. to 500.degree. C. at a rate of
3.degree. C./min. The storage modulus at 25.degree. C. was measured
to be 5757 MPa.
[0146] Tensile properties (including % elongation at break) of the
films were measured on an Instron model 3345 instrument. Crosshead
gap (sample test length) was 1 inch (2.54 centimeters) and width
was 0.5 inch (1.27 centimeters). Crosshead speed was 1 inch (2.54
centimeters)/min.
[0147] Results are shown in Table 1.
Example 2
10 vol % (24.70 wt %) Acicular TiO.sub.2 (FTL-110) in PMDA//ODA
[0148] The same procedure as described in Example 1 was followed,
with the following exceptions. 54.24 grams of the slurry containing
acicular TiO.sub.2 (FTL-110, 15 wt % in DMAC) was mixed with 136.15
grams of PMDA//ODA prepolymer (20 wt % in DMAC).
[0149] The material was finished with the PMDA solution to a
viscosity of 899 poise.
[0150] CTE, E' and % elongation at break were measured as in
Example 1.
[0151] Results are shown in Table 1.
Example 3
20 vol % (42.5 wt %) Acicular TiO.sub.2 (FTL-110) in PMDA//ODA
[0152] The same procedure as described in Example 1 was followed,
with the following exceptions. 57.7 grams of the slurry containing
acicular TiO.sub.2 (FTL-110, 15 wt % in DMAC, high shear mixed) was
combined with 63.3 grams of PMDA//ODA prepolymer (20.6 wt % in
DMAC).
[0153] The material was finished with the PMDA solution to a
viscosity of 1380 poise.
[0154] CTE, E' and % elongation at break were measured as in
Example 1.
[0155] Results are shown in Table 1.
Example 4
10 vol % SiC Fibers (20.1 wt %) in PMDA//ODA
[0156] The same procedure as described in Example 1 was followed,
except for the following differences. 24.75 grams of SiC fibers
(Silar.RTM. Silicon Carbide whiskers, beta form, Advanced
Composites Materials, Greer, S.C., USA) was combined with 140.25
grams of anhydrous DMAC. The slurry was blended under high shear
conditions, as described in Example 1.
[0157] 45.62 grams of this slurry was combined with 144.44 grams of
PMDA//ODA prepolymer (20.6 wt % in DMAC).
[0158] CTE, E' and % elongation at break were measured as in
Example 1.
[0159] Results are shown in Table 1.
Comparative Example 1
Unfilled PMDA//ODA
[0160] The same procedure as described in Example 1 was followed,
with the following exceptions. The slurry containing the inorganic
particles was not added to the PDMA//ODA prepolymer (prepolymer is
20 wt % in DMAC). The material was finished with the PMDA solution
to a viscosity of 890 poise.
[0161] CTE, E' and % elongation at break were measured as in
Example 1.
[0162] Results are shown in Table 1.
[0163] Comparative Examples 2-5 demonstrate the sub-micron filler
of the present disclosure present below 10 volume percent does not
produce a significant increase in storage modulus (especially
storage modulii at 500.degree. C.) or decrease CTE (relatively
minor improvement in storage modulus and CTE).
Comparative Example 2
2.5 vol % (7 wt %) Acicular TiO.sub.2 in PMDA//ODA
[0164] A procedure similar to that described in Example 1 was used,
except for the following differences. 24.08 grams of acicular
TiO.sub.2 (FTL-110, Ishihara Corporation, USA) was combined with
135.92 grams of anhydrous DMAC, and the slurry mixed at high
shear.
[0165] 10.1 grams of the slurry containing acicular TiO.sub.2 was
mixed with 109.9 grams of PMDA//ODA prepolymer.
[0166] CTE, E' and % elongation at break were measured as in
Example 1.
[0167] Results are shown in Table 1.
Comparative Example 3
5 vol % (13.5 wt %) Acicular TiO.sub.2 in PMDA//ODA
[0168] A procedure similar to that described in Example 1 was used,
except for the following differences. 24.08 grams of acicular
TiO.sub.2 (FTL-110, Ishihara Corporation, USA) was combined with
135.92 grams of anhydrous DMAC, and the slurry mixed at high
shear.
[0169] 19.1 grams of the slurry containing acicular TiO.sub.2 was
mixed with 100.9 grams of PMDA//ODA prepolymer.
[0170] CTE, E' and % elongation at break were measured as in
Example 1.
[0171] Results are shown in Table 1.
Comparative Example 4
6.5 vol % (17.1 wt %) Acicular TiO.sub.2 in PMDA//ODA
[0172] A procedure similar to that described in Example 1 was used,
except for the following differences. 24.08 grams of acicular
TiO.sub.2 (FTL-110, Ishihara Corporation, USA) was combined with
135.92 grams of anhydrous DMAC, and the slurry mixed at high
shear.
[0173] 23.96 grams of the slurry containing acicular TiO.sub.2 was
mixed with 96.1 grams of PMDA//ODA prepolymer.
[0174] CTE, E' and % elongation at break were measured as in
Example 1.
[0175] Results are shown in Table 1.
Comparative Example 5
8.5 vol % (21.6 wt %) Acicular TiO.sub.2 in PMDA//ODA
[0176] A procedure similar to that described in Example 1 was used,
except for the following differences. 24.08 grams of acicular
TiO.sub.2 (FTL-110, Ishihara Corporation, USA) was combined with
135.92 grams of anhydrous DMAC, and the slurry mixed at high
shear.
[0177] 30.0 grams of the slurry containing acicular TiO.sub.2 was
mixed with 90.0 grams of PMDA//ODA prepolymer.
[0178] CTE, E' and % elongation at break were measured as in
Example 1.
[0179] Results are shown in Table 1.
Comparative Example 6
15 vol. % (34.3 wt %) Less than 3:1 Aspect Ratio TiO.sub.2 in
PMDA//ODA
[0180] Comparative Example 6 demonstrates that filler having an
aspect ratio less than 3:1 produces a film with lower storage
modulus and higher CTE compared to Example 1 which has sub-micron
filler with an aspect ratio of at least 3:1 at 15 volume percent.
The film was brittle on the edges, and would not be viable in a
commercial manufacturing process.
[0181] The same procedure as described in Example 1 was followed,
with the following exceptions. 33.84 grams of the slurry containing
Du Pont Light Stabilized Titania, 210 (Du Pont, Wilmington, Del.,
25 wt % in DMAC, high shear mixed) was combined with 86.2 grams of
PMDA//ODA prepolymer (20.6 wt % in DMAC).
[0182] The material was finished with the PMDA solution to a
viscosity of 1100 poise.
[0183] Du Pont Titania 210 is a fine white powder with a
distribution of particles centered in the range of 130-140 nm on a
weight basis. The particles are roughly spherical.
[0184] CTE, E' and % elongation at break were measured as in
Example 1.
[0185] Results are shown in Table 1.
Comparative Example 7
Unfilled BPDA//PPD
[0186] The same procedure as described for Comparative Example 8
was followed, except that acicular TiO.sub.2 was not added to the
formulation.
[0187] CTE, E' and % elongation at break were measured as in
Example 1.
[0188] Results are shown in Table 1.
[0189] Comparative Examples 8-9 demonstrate that the sub-micron
filler of the present disclosure does not behave predictably in all
polyimides. In the case of a BPDA//PPD system, CTE dramatically
increases (greater than a factor of 2) with approximately 15 vol %
of acicular of TiO.sub.2 is introduced.
Comparative Example 8
14.64 vol % (33.7 wt %) Acicular TiO.sub.2 (FTL-110) in
BPDA//PPD
[0190] CTE increased with the introduction of acicular
TiO.sub.2.
[0191] BPDA//PPD prepolymer (69.3 g of a 17.5 wt % solution in
anhydrous DMAC) was combined with 5.62 g of acicular TiO.sub.2
(FTL-110, Ishihara Corporation, USA) and the resulting slurry was
stirred for 24 hours. In a separate container, a 6 wt % solution of
pyromellitic anhydride (PMDA) was prepared by combining 0.9 g of
PMDA (Aldrich 412287, Allentown, Pa.) and 15 ml of DMAC.
[0192] The PMDA solution was slowly added to the prepolymer slurry
to achieve a final viscosity of 653 poise. The formulation was
stored overnight at 0.degree. C. to allow it to degas.
[0193] The formulation was cast using a 25 mil doctor blade onto a
surface of a glass plate to form a 3''.times.4'' film. The glass
was pretreated with a release agent to facilitate removal of the
film from the glass surface. The film was allowed to dry on a hot
plate at 80.degree. C. for 20 minutes. The film was subsequently
lifted off the surface, and mounted on a 3''.times.4'' pin
frame.
[0194] After further drying at room temperature under vacuum for 12
hours, the mounted film was placed in a furnace (Thermolyne, F6000
box furnace). The furnace was purged with nitrogen and heated
according to the following temperature protocol:
TABLE-US-00001 125.degree. C. (30 min) 125.degree. C. to
350.degree. C. (ramp at 4.degree. C./min) 350.degree. C. (30 min)
350.degree. C. to 450.degree. C. (ramp at 5.degree. C./min)
450.degree. C. (20 min) 450.degree. C. to 40.degree. C. (cooling at
8.degree. C./min)
[0195] CTE, E' and % elongation at break were measured as in
Example 1.
[0196] Results are shown in Table 1.
Comparative Example 9
14.64 vol % Acicular TiO.sub.2 (FTL-110) in BPDA//PPD
[0197] The elongation to break is very low. The film is too brittle
to be manufacturable.
[0198] The same procedure as described in Example 1 was used,
except for the following differences. 33.99 grams of acicular
TiO.sub.2 (FTL-110, Ishihara Corporation, USA) was combined with
191.9 grams of anhydrous DMAC. This slurry was mixed at high shear
for approximately 10 to 15 minutes using Silverson Model L4RT
high-shear mixer (Silverson Machines, LTD, Chesham Baucks, England)
equipped with a square-hole, high-shear screen (with a blade speed
of approximately 4000 rpm).
[0199] 129.25 g of BPDA//PPD prepolymer (17.5 wt % solution in
anhydrous DMAC) was combined with 69.335 grams of the slurry
containing acicular TiO.sub.2. The resulting slurry was stirred for
24 hours. In a separate container, a 6 wt % solution of
pyromellitic anhydride (PMDA) was prepared by combining 0.9 g of
PMDA (Aldrich 412287, Allentown, Pa.) and 15 ml of DMAC.
[0200] The PMDA solution was slowly added to the prepolymer slurry
to achieve a final viscosity of 998 poise.
[0201] After chemical imidization the film was lifted off of the
glass surface, and mounted on a 3''.times.4'' pin frame. The
mounted film was placed in a furnace (Thermolyne, F6000 box
furnace). The furnace was purged with nitrogen and heated according
to the following temperature protocol:
TABLE-US-00002 125.degree. C. (30 min) 125.degree. C. to
350.degree. C. (ramp at 4.degree. C./min) 350.degree. C. (30 min)
350.degree. C. to 450.degree. C. (ramp at 5.degree. C./min)
450.degree. C. (20 min) 450.degree. C. to 40.degree. C. (cooling at
8.degree. C./min)
[0202] CTE, E' and % elongation at break were measured as in
Example 1.
[0203] Results are shown in Table 1.
Comparative Example 10
Unfilled PMDA//ODA
[0204] Three 180 g portions of a prepolymer of PMDA and ODA
(prepared in DMAC at about 20.6%, approximately 50 poise viscosity)
were diluted to 18% polymer solids via the addition of 26 g of DMAC
to give three 206 g portions of diluted polymers. One of these
three diluted prepolymer samples was reacted ("finished") to a
viscosity of about 2100 poise (Brookfield DV-II+ viscometer with a
#LV5 spindle) by stepwise additions of a 6 wt % PMDA solution in
DMAC with thorough mixing to increase the molecular weight
(hereafter referred to as "finished polymer"). After pressure
filtering the solution through a polypropylene screen filter disk
(45 micron), the solution was degassed under vacuum to remove air
bubbles and then this solution was cast onto a letter size sheet of
clear polyester film (approximately 3 mil thick). The polyamic acid
coating on the polyester sheet was subsequently immersed in a bath
containing a 1/1 v/v mixture of acetic anhydride and 3-picoline.
After about 2 minutes, once the partially imidized coating began to
separate from the polyester sheet, it was removed from the bath and
pinned on a approximately 8''.times.8'' pin frame and allow to
stand at room temperature in a lab hood for about 10-20 min. Next,
the film on the pin frame was placed in a nitrogen purged oven and
after purging at about 40.degree. C. for 30 minutes, this oven was
ramped to 320.degree. C. over 70 minutes, held there for 30
minutes, then ramped to 450.degree. C. over about 16 minutes, and
held there for 4 minutes, in order to cure to polyimide. After
cooling, the resulting 2.4 mil (61 micron) film was removed from
the oven and pin frame.
[0205] Storage modulus (E') by Dynamic Mechanical Analysis (TA
Instruments, DMA-2980, 5.degree. C./min) was measured by heating
from room temperature to 500.degree. C. at 5.degree. C./min.
[0206] Coefficient of thermal expansion (CTE) by Thermal Mechanical
Analysis (TA Instruments, TMA-2940, heat 10.degree. C./min, up to
460.degree. C., then cool and reheat to 500.degree. C.) was
evaluated between 50-350.degree. C. on the reheat.
[0207] % Tensile Elongation (Instron model 3345 tensile tester)-0.5
in specimen width, 1 inch (2.54 centimeters) gauge length, 1 inch
(2.54 centimeters)/min crosshead speed.
[0208] Results are shown in Table 1.
Comparative Example 11
5.4 vol % (10 wt %) Talc in PMDA//ODA
[0209] Comparative Example 11 demonstrates talc below about 5.5
volume percent does not behave predictably.
[0210] In a similar manner to Comparative Example 10, a portion of
a prepolymer of PMDA and ODA (prepared in DMAC at about 20.6%,
approximately 50 poise viscosity) was diluted to 18% polymer solids
via the addition of DMAC. Then, the prepolymer was blended with
SF310 talc for several minutes in a Thinky ARE-250 centrifugal
mixer to yield a dispersion of the filler in the PAA solution, to
achieve about a 10 wt % loading in the PI film. Finishing,
filtration, casting and curing was similar to as described in
Comparative Example 10. A 1 mil (25 micron) film was produced.
[0211] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0212] Results are shown in Table 1.
[0213] Examples 5-9 demonstrate talc above about 5.5 volume percent
significantly increase storage modulus and lower CTE while
maintaining adequate elongation to break.
Example 5
14.0 vol % (24 wt %) Talc in PMDA//ODA
[0214] The same procedure as described in Example 1 was followed,
with the following exceptions. 25 grams of talc (Flextalc 610, Kish
Company, Inc., Mentor, Ohio) was mixed, at high shear, with 141
grams of anhydrous DMAC.
[0215] 55.9 grams of this slurry was mixed with 134.7 grams of
PMDA//ODA prepolymer.
[0216] CTE, E' and % elongation at break were measured as in
Example 1.
[0217] Results are shown in Table 1.
Example 6
18 vol % (30 wt %) Talc in PMDA//ODA
[0218] In a similar manner to Comparative Example 11, the second of
the 206 g portions of the diluted prepolymer from Comparative
Example 10 was blended with 14.77 g of Flextalc 610 (Lot M1085,
Kish Co., Mentor, Ohio).
[0219] Finishing, filtration, casting and curing was similar to as
described in Comparative Example 10. Filler loading was
approximately 30 wt % in the polyimide film. A 3.2 mil (81 micron)
film was produced.
[0220] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0221] Results are shown in Table 1.
Example 7
18.1 vol % (30 wt %) Talc in PMDA//ODA
[0222] In a similar manner to Comparative Example 11, the third of
the 206 g portions of the diluted prepolymer from Comparative
Example 10 was blended with 14.77 g of SF310 talc (Kish Co.,
Mentor, Ohio). Finishing, filtration, casting and curing was
similar to as described in Comparative Example 10. Filler loading
was approximately 30 wt % in the polyimide film. A 3.2 mil (81
micron) film was produced.
[0223] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0224] Results are shown in Table 1.
Example 8
34 vol % (50 wt %) Talc in PMDA//ODA
[0225] In a similar manner to Comparative Example 11, the PMDA//ODA
prepolymer was blended with SF310 talc to achieve about a 50 wt %
loading in the PI film. Finishing, filtration, casting and curing
was similar to as described in Comparative Example 10 filler
loading was approximately 50 wt % in the polyimide film. A 1.8 mil
(46 micron) film was produced.
[0226] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0227] Results are shown in Table 1.
Example 9
43.6 vol % (60 wt %) Talc in PMDA//ODA
[0228] In a similar manner to Comparative Example 11, the PMDA//ODA
prepolymer was blended with SF310 talc to achieve about a 60 wt %
loading in the PI film. Finishing, filtration, casting and curing
was similar to as described in Comparative Example 10. A 1.3 mil
(33 micron) film was produced.
[0229] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0230] Results are shown in Table 1.
[0231] Examples 10-11 demonstrate sub-micron fillers of the present
disclosure in polyimide copolymers above 10 volume percent
significantly increases storage modulus and lowers CTE when
compared to unfilled copolymer in Comparative Example 13.
Example 10
18.1 vol % (30 wt %) Talc in Random Copolymer of PMDA//ODA/PPD
100//70/30
[0232] In a similar manner to Comparative Example 11, a 186.87 g
portion of the prepolymer from Comparative Example 13 was blended
with 13.13 g of Flextalc 610 (Lot M6734, Kish Co., Mentor, Ohio).
Finishing, filtration, casting and curing was similar to as
described in Comparative Example 10. Filler loading was
approximately 30 wt % in the polyimide film. A 2.2 mil (56 micron)
film was produced.
[0233] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0234] Results are shown in Table 1.
Example 11
12.6 vol % (30 wt %) Acicular TiO.sub.2 in Random Copolymer of
PMDA//ODA/PPD 100//70/30
[0235] In a similar manner to Comparative Example 11, a 173 g
portion of the prepolymer from Comparative Example 13 was blended
with 27 g of a milled/dispersed 45 wt % slurry of acicular
TiO.sub.2 (FTL-110 powder from Ishihara Corp. (USA)) in DMAC.
Finishing, filtration, casting and curing was similar to as
described in Comparative Example 10. Filler loading was
approximately 30 wt % in the polyimide film. A 1.1 mil (28 micron)
film was produced.
[0236] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0237] Results are shown in Table 1.
Comparative Example 12
Unfilled Random Copolymer of PMDA//ODA/PPD 100//70/30
[0238] In a 1.5 liter beaker inside a nitrogen purged glove box,
15.118 g of PPD (0.1398 moles) and 65.318 g (0.3262 moles) ODA were
added to 779.2 g of DMAC well agitated with a mechanical stirrer.
After brief mixing at room temperature, 99.612 g (0.4567 moles) of
PMDA was slowly added to maintain the temperature below 40.degree.
C., followed by 41.0 g DMAC and the reaction was allowed to proceed
for about 2 hours. The resulting prepolymer solution (98% overall
stoichiometry of dianhydride to diamine, 18% polymer solids), was
decanted into a bottle and stored in a freezer until use. A portion
of this prepolymer was finished similarly as in Example A,
filtered, and then a film was cast and cured similarly to
Comparative Example 10. A 1.4 mil (36 micron) film was
produced.
[0239] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0240] Results are shown in Table 1.
[0241] Examples 12 and 13 demonstrate that a mixture of sub-micron
fillers of the present disclosure significantly increase storage
modulus and lower CTE when compared to unfilled polyimide in
Comparative Example 10.
Example 12
10 wt % Talc, 20 wt % Acicular TiO.sub.2 in Polymer of
PMDA//ODA
[0242] A 168.21 g portion of a prepolymer of PMDA and ODA (prepared
in DMAC at about 20.6%, approximately 50 poise viscosity) was
blended together with 4.60 g SF310 talc and 20.46 g FTL-110
TiO.sub.2 (45% slurry as described in example 11 to achieve 10 wt %
and 20 wt % loading respectively of the sub-micron fillers in the
PI film (30 wt % total). Finishing, filtration, casting and curing
was similar to as described in Comparative Example 10. A 1.0 mil
(25 micron) film was produced.
[0243] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0244] Results are shown in Table 1.
Example 13
20 wt % Talc, 10 wt % Acicular TiO.sub.2 in Polymer of
PMDA//ODA
[0245] In a similar manner to Example 12, a 173.13 portion of the
PMDA//ODA prepolymer was blended together with 9.45 g SF310 talc
and 10.50 g FTL-110 TiO.sub.2 (45% slurry as described in Example
11) to achieve 20 wt % and 10 wt % loading respectively of the
sub-micron fillers in the PI film (30 wt % total). Finishing,
filtration, casting and curing was similar to as described in
Comparative Example 10. A 2.2 mil (56 micron) film was
produced.
[0246] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0247] Results are shown in Table 1.
[0248] Examples 14 and 15 demonstrate a TiO.sub.2 sub-micron filler
of the present disclosure does not behave in the same manner in all
polyimides in regards to CTE.
Example 14
11.7 vol % Acicular TiO.sub.2 (28.23 wt %) in Block Copolymer of
PMDA//ODA/PPD 100//80/20
[0249] High aspect ratio TiO.sub.2 in the block copolymer of
example 14 significantly increases storage modulus while largely
maintaining CTE compared to unfilled block copolymer of Comparative
Example 13.
[0250] A similar procedure as described in Example 1 was used,
except for the following differences. To prepare the prepolymer,
1.36 grams of PPD was combined with 110.0 grams of anhydrous DMAC
and stirred, with gentle heating at 40.degree. C. for approximately
20 minutes. 2.71 grams of PMDA was then added to this mixture to
create the first block, which was stirred with gentle heating
(35-40.degree. C.) for approximately 2.5 hours. The mixture was
allowed to cool to room temperature.
[0251] To this formulation, 10.10 grams of ODA was added and
allowed to dissolve in to the formulation for about 5 minutes. An
ice water bath was then used to control the temperature during the
subsequent PMDA addition. 10.9 g PMDA was slowly added to this
mixture. An addition 15 grams of DMAC was added to the formulation
and the reaction was allowed to stir with gentle heat
(30-35.degree. C.) for 90 minutes. The mixture was allowed to stir
at room temperature for approximately 18 hours.
[0252] In a separate container, 20.88 grams of acicular TiO.sub.2
(FTL-11) was combined with 25.52 g of anhydrous DMAC and 0.426 g of
Solplus D540 (Lubrizol) and milled for 24 hours in a jar mill using
8 mm spherical milling media.
[0253] 14.2 gram of the slurry containing TiO.sub.2 was mixed with
105.8 grams of the prepolymer formulation described above.
[0254] A modified heating procedure was used, as shown below:
TABLE-US-00003 40.degree. C. to 125.degree. C. (ramp at 4.degree.
C./min) 125.degree. C. (soak 30 min) 125.degree. C. to 350.degree.
C. (ramp at 4.degree. C./min) 350.degree. C. to 350.degree. C.
(soak 30 min) 350.degree. C. to 450.degree. C. (ramp at 5.degree.
C./min) 450.degree. C. (soak 20 min)
[0255] CTE, E' and % elongation at break were measured as in
Example 1.
[0256] Results are shown in Table 1.
Example 15
17.5 vol % Acicular TiO.sub.2 (38.5 wt %) in Block Copolymer of
PMDA//ODA/PPD 100//80/20
[0257] High aspect ratio TiO.sub.2 in the block copolymer of 15
significantly increases storage modulus while slightly decreasing
CTE in the transverse direction compared to unfilled block
copolymer of Comparative Example 13.
[0258] A similar procedure as described in Example 1 was used,
except for the following differences. To prepare the prepolymer,
1.36 grams of PPD was combined with 113.0 grams of anhydrous DMAC
and stirred, with gentle heating at 40.degree. C. for approximately
20 minutes. 2.71 grams of PMDA was then added to this mixture to
create the first block, which was stirred with gentle heating
(35-40.degree. C.) for approximately 2.5 hours. The mixture was
allowed to cool to room temperature.
[0259] To this formulation, 10.10 grams of ODA was added and
allowed to dissolve in to the formulation for about 5 minutes. An
ice water bath was then used to control the temperature during the
subsequent PMDA addition. 10.9 g PMDA was slowly added to this
mixture. An additional 12 grams of DMAC was added to the
formulation and the reaction was allowed to stir with gentle heat
(30-35 degrees) for 90 minutes. The mixture was allowed to stir at
room temperature for approximately 18 hours.
[0260] In a separate container, 20.88 grams of acicular TiO.sub.2
(FTL-11) was combined with 25.52 g of anhydrous DMAC and 0.426 g of
Solplus D540 (Lubrizol) and milled for 24 hours in a 4'' (internal
diameter) nylon jar mill using 8 mm spherical milling media,
turning at 80 rpm.
[0261] 15.34 gram of the slurry containing TiO.sub.2 was mixed with
72.0 grams of the prepolymer formulation described above.
[0262] A modified heatina procedure was used. as shown below:
TABLE-US-00004 40.degree. C. to 125.degree. C. (ramp at 4.degree.
C./min) 125.degree. C. (soak 30 min) 125.degree. C. to 350.degree.
C. (ramp at 4.degree. C./min) 350.degree. C. to 350.degree. C.
(soak 30 min) 350.degree. C. to 450.degree. C. (ramp at 5.degree.
C./min) 450.degree. C. (soak 20 min)
[0263] CTE, E' and % elongation at break were measured as in
Example 1.
[0264] Results are shown in Table 1.
Comparative Example 13
Unfilled Block Copolymer of PMDA//ODA/PPD 100//80/20
[0265] The same procedure was used as described in Example 15 was
used, except that the acicular TiO.sub.2 slurry was not added to
the formulation. The final viscosity of the formulation was
1000-1200 poise. CTE, E' and % elongation at break were measured as
in Example 1.
[0266] Results are shown in Table 1.
Example 16
12.6 vol % Acicular TiO.sub.2 (30 wt %) Filled Block Copolymer of
PMDA//ODA/PPD 100//70/30
[0267] Example 16 demonstrates acicular TiO.sub.2 sub-micron filler
of the present disclosure does not behave in the same manner in all
polyimides in regards to CTE. CTE increases compared to unfilled
block copolymer in Comparative Example 14 but still remains in a
desirable range.
[0268] In a similar manner to Comparative Example 11, a 173 g
portion of the prepolymer from Comparative Example 14 was blended
with 27 g of a milled/dispersed 45 wt % slurry of acicular
TiO.sub.2 (FTL-110 powder from Ishihara Corp. (USA)) in DMAC.
Finishing, filtration, casting and curing was similar to as
described in Comparative Example 10. Filler loading was
approximately 30 wt % in the polyimide film. A 3.0 mil (76 micron)
film was produced.
[0269] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0270] Results are shown in Table 1.
Comparative Example 14
Unfilled Block Copolymer of PMDA//ODA/PPD 100//70/30
[0271] In a 1.5 liter beaker inside a nitrogen purged glove box,
15.115 g of PPD were added to 396.7 g of DMAC well agitated with a
mechanical stirrer. After brief mixing at room temperature (some
but not all PPD had dissolved), 28.962 g of PMDA was slowly added
to maintain the temperature below 40.degree. C. The monomers
dissolved and reacted and the polyamic acid (PAA) solution was
allowed to stir for 1 hr. Afterwards, the solution was diluted with
382.3 g of DMAC and then 65.304 g ODA was added. This solution was
stirred for 30 min and the ODA dissolved into the PAA solution.
Subsequently, 70.627 g of PMDA was slowly added, followed by 41.0 g
DMAC and the reaction was allowed to proceed for about 2 hours. The
resulting prepolymer solution (98% overall stoichiometry of
dianhydride to diamine, 18% polymer solids), was decanted into a
bottle and stored in a freezer until use. A 180 g portion of this
prepolymer was finished as in Comparative Example 10 to about 2200
poise, filtered, and then a film was cast and cured similarly to
Comparative Example 10. Properties of the resulting 2.2 mil (56
micron) film.
[0272] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0273] Results are shown in Table 1.
[0274] Examples 17-20 demonstrate block copolymer with talc above
about 5.5 volume percent significantly increase storage modulus and
maintain CTE while maintaining adequate elongation to break.
Example 17
18.1 vol % Talc (30 wt %) Filled Block Copolymer of PMDA//ODA/PPD
100//70/30
[0275] A 186.87 g portion of the prepolymer prepared in Comparative
Example 14 was blended with 13.13 g of SF-310 talc (Lot M685, Kish
Co., Mentor, Ohio) in a similar manner to Comparative Example 11.
This filler containing PAA solution was finished similarly as in
Comparative Example 10 to yield a viscosity of ca. 2000 poise. The
solution was pressured filtered through a 45 micron polypropylene
screen and degassed under vacuum to remove air bubbles. A film was
cast and cured similarly Comparative
Example 10
Filler Loading was Approximately 30 wt % in the Polyimide Film
[0276] A 2.6 mil (66 micron) film was produced.
[0277] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0278] Results are shown in Table 1.
Example 18
18.1 vol % Talc (30 wt %) Filled Block Copolymer of PMDA//ODA/PPD
100//70/30
[0279] In a similar manner to Comparative Example 11, a 186.87 g
portion of the prepolymer from Comparative Example 14 was blended
with 13.13 g of Flextalc 610 (Lot M1085, Kish Co., Mentor, Ohio).
Finishing, filtration, casting and curing was similar to as
described in Comparative Example 10. Filler loading was
approximately 30 wt % in the polyimide film. A 2.9 mil (74 micron)
film was produced.
[0280] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0281] Results are shown in Table 1.
Example 19
25.6 vol % Talc (40 wt %) Filled Block Copolymer of PMDA//ODA/PPD
100//70/30
[0282] In a similar manner to Comparative Example 15, the
PMDA//ODA/PPD 100//70/30 block prepolymer was blended with SF310
talc to achieve about a 40 wt % loading in the PI film. Finishing,
filtration, casting and curing was similar to as described in
Comparative Example 10. A 1.8 mil (46 micron) film was
produced.
[0283] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0284] Results are shown in Table 1.
Example 20
34 vol % Talc (50 wt %) Filled Block Copolymer of PMDA//ODA/PPD
100//70/30
[0285] In a similar manner to Comparative Example 14, a block
prepolymer was prepared with a 70/30 ratio of ODA to PPD. Then in a
similar manner to
[0286] Comparative Example 11, a 171.75 g portion of this
prepolymer was blended with 28.255 g SF310 talc to achieve about a
50 wt % loading in the PI film. Finishing, filtration, casting and
curing was similar to as described in Comparative Example 10. A 1.5
mil (38 micron) film was produced. CTE, E' and % elongation at
break were measured as in Comparative Example 10.
[0287] Results are shown in Table 1.
Comparative Example 15
5.4 vol % Talc (10 wt %) Filled Block Copolymer of PMDA//ODA/PPD
100//70/30
[0288] Comparative Example 15 demonstrates talc below about 5.5
volume percent does not significantly increase storage modulus.
[0289] In a similar manner to Comparative Example 14, a block
prepolymer was prepared with a 70/30 ratio of ODA to PPD. Then in a
similar manner to Comparative Example 11, a 187.16 g portion of
this prepolymer was blended with 3.48 g SF310 talc to achieve about
a 10 wt % loading in the PI film. Finishing, filtration, casting
and curing was similar to as described in Comparative Example 10. A
1.7 mil (43 micron) film was produced.
[0290] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0291] Results are shown in Table 1.
[0292] The examples 21-24 illustrate the ability to include
additional co-monomers in the compositions of the present invention
and still achieve desirable properties.
Example 21
18.1 vol % (30 wt %) Talc Filled Block Copolymer of
PMDA/BPDA//ODA/PPD 95/5//70/30
[0293] In a similar manner to Comparative Example 14, a prepolymer
was produced from 14.988 g PPD and 28.720 g PMDA in 393.4 g DMAC,
followed by dilution with 386.8 g DMAC, then addition of 64.758 g
ODA, and then 6.796 g of BPDA (which was allowed to
dissolve/react), then 64.998 g of PMDA, followed by 41.0 g DMAC. A
186.8 g portion of this prepolymer was blended with 13.17 g SF310
talc (Lot M685, Kish Co., Mentor, Ohio) similar to Comparative
Example 11, finished as in Comparative Example 10, filtered, and
then a film was cast and cured similarly to Comparative Example 10.
A 2.0 mil (51 micron) film was produced.
[0294] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0295] Results are shown in Table 1.
Example 22
12.6 vol % (30 wt %) acicular TiO.sub.2 Filled Block Copolymer of
PMDA//BPDA//ODA/PPD 95/5//70/30
[0296] In a similar manner to Example 21, a 172.7 g portion of the
prepolymer from Example 21 was blended with a 27.3 g portion of the
TiO.sub.2 slurry as described in Example 16. Finishing, filtration,
casting and curing was similar to as described in Comparative
Example 10. Filler loading was approximately 30 wt % in the
polyimide film. A 2.2 mil (56 micron) film was produced.
[0297] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0298] Results are shown in Table 1.
Example 23
18.1 vol % (30 wt %) Talc Filled Block Copolymer of
PMDA/BPDA//ODA/PPD 75/25//70/30
[0299] In a similar manner to Comparative Example 14, a prepolymer
was produced from 14.407 g PPD and 27.607 g PMDA in 378.1 g DMAC,
followed by dilution with 401 g DMAC, then addition of 62.249 g
ODA, and then 32.666 g of BPDA (which was allowed to
dissolve/react), then 43.106 g of PMDA, followed by 41.0 g DMAC. A
186.8 g portion of this prepolymer was blended with 13.17 g SF310
talc (Lot M685, Kish Co., Mentor, Ohio) similar to Comparative
Example 11, finished, cast and cured similarly to Comparative
Example 10. A 1.7 mil (43 micron) film was produced.
[0300] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0301] Results are shown in Table 1.
Example 24
12.6 vol % (30 wt %) acicular TiO.sub.2 Filled Block Copolymer of
PMDA/BPDA//ODA/PPD 75/25//70/30
[0302] In a similar manner to Example 23, a 172.7 g portion of the
prepolymer from Example 23 was blended with a 27.3 g portion of the
TiO.sub.2 slurry as described in Example 16. Finishing, filtration,
casting and curing was similar to as described in Comparative
Example 10. A 2.3 mil (58 micron) film was produced.
[0303] CTE, E' and % elongation at break were measured as in
Comparative Example 10.
[0304] Results are shown in Table 1.
[0305] The following Examples demonstrate the impact on properties
of a particulate (less than 3:1 aspect ratio) vs. a high aspect
ratio (greater than 3:1 aspect ratio) platelet filler on the
properties of a polyimide film. The platelet filler results in
advantageously higher modulus and lower CTE at equivalent weight
loadings. (Note that although the average particle sizes of these
two fillers appear significantly different (platelet is
significantly larger) via particle size analysis (Horiba LA-930
particle size analyzer), it is believed that the effect on
properties is largely due to the filler shape, rather than any
differences in average particle size).
Comparative Example 16
(40 wt %) Less Than 3:1 Aspect Ratio Al.sub.2O.sub.3 (Particulate)
in PMDA//ODA
[0306] A portion of a polyamic acid prepolymer of PMDA and ODA
(prepared in DMAC at about 20.6%, approximately 50 poise viscosity)
was blended with particulate alumina filler (Martoxid MZS-1,
Albermarle Corporation) in a Silverson (model L4RT-A) high shear
mixer. The amount of alumina was chosen so as to ultimately yield a
final polyimide film with a 40 wt % loading of alumina in
polyimide. The polyamic acid was then further reacted ("finished")
to a viscosity of about 537 poise (Brookfield DV-II+ viscometer
with a #LV5 spindle) by stepwise additions of a 6 wt % PMDA
solution in DMAC with thorough mixing via a high torque mechanical
mixer/stir blade. The polymer was subsequently cast onto a glass
plate and heated to about 80.degree. C. until a tack free film was
obtained. The film was carefully peeled from the glass and placed
on a pin frame and placed in a circulating air oven and the
temperature slowly ramped to 320.degree. C. and held there for 30
minutes. Next, the film was removed from the 320.degree. C. oven
and place in a 400.degree. C. air oven for 5 minutes. Afterwards,
the polyimide film on the pin frame was removed from the oven and
allowed to cool to room temperature. The film was then separated
from the pin frame.
[0307] E' was measured as in Comparative Example 10. CTE was
measured on the same instrument and at the same rate as Comparative
Example 10 except that the sample was heated to 380.degree. C.,
then cooled and reheated to 380.degree. C.) and evaluated between
50-350.degree. C. on the reheat.
[0308] Results are shown in Table 1.
Example 25
(40 wt %) Greater than 3:1 Aspect Ratio Al.sub.2O.sub.3 (Platy) in
PMDA//ODA
[0309] In a similar manner to Comparative Example 16, a portion of
the PMDA//ODA prepolymer was blended with a platelet-shaped alumina
("Platyl" from Advanced Nanotechnology Limited, Australia) at the
same loading level as the particular alumina from Comparative
Example 16 and finished to a Brookfield viscosity of 502 poise).
This filled polymer solution was cast and thermally cured as in
Comparative Example 16.
[0310] E' was measured as in Comparative Example 10. CTE was
measured on the same instrument and at the same rate as Comparative
Example 16.
[0311] Results are shown in Table 1.
[0312] Note that not all of the activities described above in the
general description or the examples are required, that a portion of
a specific activity may not be required, and that further
activities may be performed in addition to those described. Still
further, the order in which each of the activities are listed is
not necessarily the order in which they are performed. After
reading this specification, skilled artisans will be capable of
determining what activities can be used for their specific needs or
desires.
[0313] In the foregoing specification, the invention has been
described with reference to specific embodiments. However, one of
ordinary skill in the art appreciates that various modifications
and changes can be made without departing from the scope of the
invention as set forth in the claims below. Accordingly, the
specification and any figures are to be regarded in an illustrative
rather than a restrictive sense and all such modifications are
intended to be included within the scope of the invention.
[0314] Benefits, other advantages, and solutions to problems have
been described above with regard to specific embodiments. However,
the benefits, advantages, solutions to problems, and any element(s)
that may cause any benefit, advantage, or solution to occur or
become more pronounced are not to be construed as a critical,
required, or essential feature or element of any or all the
claims.
[0315] When an amount, concentration, or other value or parameter
is given as either a range, preferred range or a list of upper
values and lower values, this is to be understood as specifically
disclosing all ranges formed from any pair of any upper range limit
or preferred value and any lower range limit or preferred value,
regardless of whether ranges are separately disclosed. Where a
range of numerical values is recited herein, unless otherwise
stated, the range is intended to include the endpoints thereof, and
all integers and fractions within the range. It is not intended
that the scope of the invention be limited to the specific values
recited when defining a range.
TABLE-US-00005 TABLE 1 Equivalent vol %, using density of % 1.42
g/c for TENSILE polymer, 4.2 g/cc E' at 50.degree. C. ELON- POLYMER
for acicular TiO.sub.2, (unless E' at CTE CTE GATION (ODA/PPD 2.75
g/cc for talc, otherwise 300.degree. C., E' at 480.degree. C. MD,
TD, to Break ratio) Filler wt % 3.22 g/cc for SiC noted) GPa GPa
GPa ppm/C ppm/C MD/TD 1 PMDA/ODA Acicular TiO.sub.2, 34.3 15.00 5.7
(25.degree. C.) 3.2 0.854 (500.degree. C.) 24.0 26.4 35.6 MD 2
PMDA/ODA Acicular TiO.sub.2, 24.7 10.00 6.2 (25.degree. C.) 3.5
0.875 (500.degree. C.) 24.6 32.4 3 PMDA/ODA Acicular TiO.sub.2,
42.5 20.00 6.14 (25.degree. C.) 3.6 1.02 (500.degree. C.) 27.1 17.4
4 PMDA/ODA SiC fiber 20.1 10.00 5.3 (25.degree. C.) 2.7 0.27
(500.degree. C.) 22.0 31.2 35.8 MD Comp. 1 PMDA/ODA None 0 0.00 3.5
(25.degree. C.) 1.8 0.4 (500.degree. C.) 38.4 39.6 Comp. 2 PMDA/ODA
acicular TiO.sub.2, 7 2.50 3.9 (25.degree. C.) 2.1 0.51
(500.degree. C.) 38.0 38.6 Comp. 3 PMDA/ODA acicular TiO.sub.2,
13.5 5.00 4.4 (25.degree. C.) 2.3 0.55 (500.degree. C.) 31.0 36.8
Comp. 4 PMDA/ODA acicular TiO.sub.2, 17.1 6.50 4.4 (25.degree. C.)
2.4 0.61 (500.degree. C.) 30.0 33.8 Comp. 5 PMDA/ODA acicular
TiO.sub.2, 21.6 8.50 4.3 (25.degree. C.) 2.2 0.51 (500.degree. C.)
32.9 34.1 Comp 6 PMDA/ODA Spherical 34.3 15.00 4.42 (25.degree. C.)
2.2 0.48 (500.degree. C.) 37.7 43.5 TiO.sub.2, Comp. 7 BPDA/PPD
None 0 0.00 10.8 Comp. 8 BPDA/PPD acicular TiO.sub.2, 33.7 14.64
23.0 Comp. 9 BPDA/PPD acicular TiO.sub.2, 33.7 14.64 6 all rigid
rod Comp. 10 PMDA/ODA None 0 0.00 2.9 0.29 43.0 42.0 Comp. 11
PMDA/ODA Talc 10 5.42 3.0 0.21 29.0 23.0 126/136 5 PMDA/ODA Talc 24
14.02 5.7 (25.degree. C.) 25.4 6 PMDA/ODA Talc 30 18.08 5.8 0.78
24.0 23.0 178/181 7 PMDA/ODA Talc 30 18.08 5.4 0.86 21.0 19.0
171/148 8 PMDA/ODA Talc 50 34.00 8.9 1.20 11.0 13.0 56/73 9
PMDA/ODA Talc 60 43.60 11.1 1.96 8.0 9.0 42/56 10 PMDA// Talc 30
18.08 7.1 1.17 13.0 17.0 63/41 ODA/PPD Random (70/30) 11 PMDA//
acicular TiO.sub.2, 30 12.64 6.3 0.87 18.0 25.0 27/45 ODA/PPD
Random (70/30) Comp. 12 PMDA// None 0 0.00 4.5 0.45 23.0 25.0
122/123 ODA/PPD Random (70/30) 12 PMDA/ODA Talc 10 wt % 7.3 0.94
21.0 29.0 69/72 TiO.sub.2, 20 wt % 13 PMDA/ODA Talc 20 wt % 5.9
0.94 19.0 21.0 76/78 TiO.sub.2, 10 wt % 14 PMDA// acicular
TiO.sub.2, 28.23 11.74 6.8 (25.degree. C.) 4.0 1.5 (500.degree. C.)
23.0 21.0 ODA/PPD 80/20 15 PMDA// acicular TiO.sub.2, 38.5 17.50
7.1 (25.degree. C.) 4.1 1.3 (500.degree. C.) 20.0 17.5 ODA/PPD
80/20 Comp. 13 PMDA// None 0 0.00 3.5 2.0 1.2 (500.degree. C.) 23.0
24.0 ODA/PPD 80/20 16 PMDA// acicular TiO.sub.2, 30 12.64 7.5 1.22
15.0 14.0 41/53 ODA/PPD 70/30 Comp. 14 PMDA// None 0 0.00 5.2 0.70
7.0 9.0 107/124 ODA/PPD 70/30 17 PMDA// Talc 30 18.08 6.9 1.24 9.0
9.0 84/69 ODA/PPD 70/30 18 PMDA// Talc 30 18.08 7.4 1.34 8.0 13.0
62/54 ODA/PPD 70/30 19 PMDA// Talc 40 25.62 9.5 1.80 10.0 9.0 58/52
ODA/PPD 70/30 20 PMDA// Talc 50 34.00 11.1 2.60 8.0 7.0 31/41
ODA/PPD 70/30 Comp. 15 PMDA// Talc 10 5.42 5.4 0.72 9.0 4.0 60/66
ODA/PPD 70/30 21 PMDA/BPDA// Talc 30 18.08 9.7 (25.degree. C.) 1.42
(498.degree. C.) 6.0 10.0 60/80 ODA/PPD 95/5//70/30 22 PMDA/BPDA//
acicular TiO.sub.2, 30 12.64 8.3 (25.degree. C.) 1.26 (498.degree.
C.) 11.0 17.0 40/56 ODA/PPD 95/5//70/30 23 PMDA/BPDA// Talc 30
18.08 10.9 (25.degree. C.) 0.88 (498.degree. C.) 8.0 11.0 51/38
ODA/PPD 75/25//70/30 24 PMDA/BPDA// acicular TiO.sub.2, 30 12.64 9
(25.degree. C.) 0.61 (498.degree. C.) 11.0 20.0 32/68 ODA/PPD
75/25//70/30 Comp. 16 PMDA/ODA particle Al.sub.2O.sub.3 40 4.1 0.28
52.0 25 PMDA/ODA platy Al.sub.2O.sub.3 40 6.6 1.10 20.0
* * * * *