U.S. patent application number 16/681172 was filed with the patent office on 2020-05-14 for multilayer polymer film.
The applicant listed for this patent is DUPONT ELECTRONICS, INC.. Invention is credited to Leopoldo Alejandro Carbajal, KOSTANTINOS KOURTAKIS, Mark Allan Lamontia, Gene M. Rossi, Mobin Yahyazadehfar.
Application Number | 20200147943 16/681172 |
Document ID | / |
Family ID | 68808558 |
Filed Date | 2020-05-14 |
![](/patent/app/20200147943/US20200147943A1-20200514-M00001.png)
United States Patent
Application |
20200147943 |
Kind Code |
A1 |
KOURTAKIS; KOSTANTINOS ; et
al. |
May 14, 2020 |
Multilayer Polymer Film
Abstract
In a first aspect, a multilayer polymer film includes a first
substantially transparent polymer layer having a first elastic
modulus and a second substantially transparent polymer layer having
a second elastic modulus. The first elastic modulus is different
from the second elastic modulus and the first and second
substantially transparent polymer layers are bonded by
consolidation. In a second aspect, a cover window includes the
multilayer polymer film of the first aspect and a layer of a
transparent material. The layer of a transparent material has a
speed of sound of at least 2000 m/s. In a third aspect, an
electronic device includes the cover window of the second
aspect.
Inventors: |
KOURTAKIS; KOSTANTINOS;
(Media, PA) ; Rossi; Gene M.; (Wilmington, DE)
; Carbajal; Leopoldo Alejandro; (Newark, DE) ;
Lamontia; Mark Allan; (Landenberg, PA) ;
Yahyazadehfar; Mobin; (West Chester, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DUPONT ELECTRONICS, INC. |
Wilmington |
DE |
US |
|
|
Family ID: |
68808558 |
Appl. No.: |
16/681172 |
Filed: |
November 12, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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62760523 |
Nov 13, 2018 |
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62760506 |
Nov 13, 2018 |
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62760499 |
Nov 13, 2018 |
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62760488 |
Nov 13, 2018 |
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62760478 |
Nov 13, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 7/10 20130101; B32B
27/365 20130101; B32B 2264/102 20130101; B29K 2995/0026 20130101;
B32B 2305/72 20130101; B32B 2307/412 20130101; B29K 2509/02
20130101; B32B 27/288 20130101; B32B 2250/04 20130101; B32B 2250/24
20130101; B32B 27/308 20130101; B32B 27/08 20130101; B29L 2009/00
20130101; B32B 2264/10 20130101; B29C 48/022 20190201; B32B 27/285
20130101; B32B 27/302 20130101; B32B 2307/558 20130101; B32B 7/022
20190101; B32B 7/12 20130101; B32B 27/281 20130101; B32B 27/36
20130101; B32B 27/34 20130101; B29C 48/21 20190201; B29K 2079/08
20130101; B32B 2307/51 20130101; B32B 2250/40 20130101; B32B
2457/00 20130101; B32B 27/18 20130101; B32B 27/20 20130101; B32B
2307/308 20130101; B32B 2250/02 20130101; B29K 2105/162 20130101;
B32B 2307/54 20130101; B32B 2509/00 20130101; B32B 17/064 20130101;
B32B 2605/003 20130101; B32B 2250/03 20130101; B32B 2250/05
20130101; B32B 2264/12 20130101; B32B 2457/206 20130101 |
International
Class: |
B32B 27/08 20060101
B32B027/08; B32B 27/28 20060101 B32B027/28; B32B 27/34 20060101
B32B027/34; B32B 7/12 20060101 B32B007/12 |
Claims
1. A multilayer polymer film comprising: a first substantially
transparent polymer layer having a first elastic modulus; and a
second substantially transparent polymer layer having a second
elastic modulus, wherein: the first elastic modulus is different
from the second elastic modulus; and the first and second
substantially transparent polymer layers are bonded by
consolidation.
2. The multilayer polymer film of claim 1, wherein a Mode I
interlaminar fracture toughness (G.sub.lc) between the first and
second substantially transparent polymer layers is at least 500
J/m.sup.2.
3. The multilayer polymer film of claim 1, wherein a difference
between the elastic moduli of the first and second substantially
transparent polymer layers is at least 5%.
4. The multilayer polymer film of claim 1, wherein the first
substantially transparent polymer layer, the second substantially
transparent polymer layer, or both the first and second
substantially transparent polymer layers have a speed of sound of
at least 1300 m/s.
5. The multilayer polymer film of claim 1, wherein the first
substantially transparent polymer layer, the second substantially
transparent polymer layer, or both the first and second
substantially transparent polymer layers further comprise
sub-micron fillers.
6. The multilayer polymer film of claim 1, wherein the polymer of
the first substantially transparent polymer layer is cross-linked,
the polymer of the second substantially transparent polymer layer
is cross-linked, or the polymers of both the first and second
substantially transparent polymer layers are cross-linked.
7. The multilayer polymer film of claim 1, wherein the first
substantially transparent polymer layer, the second substantially
transparent polymer layer, or both the first and second
substantially transparent polymer layers comprise a polyimide, a
polyamide imide, a block copolymer of a polyimide or a block
copolymer of a polyamide imide.
8. The multilayer polymer film of claim 7, wherein the first
substantially transparent polymer layer, the second substantially
transparent polymer layer, or both the first and second
substantially transparent polymer layers further comprise an
imidization catalyst.
9. The multilayer polymer film of claim 1, further comprising a
third substantially transparent polymer layer having a third
elastic modulus, wherein: the second substantially transparent
polymer layer is positioned between the first and third
substantially transparent polymer layers; and the second and third
substantially transparent polymer layers are bonded by
consolidation.
10. The multilayer polymer film of claim 9, wherein: (i) the second
elastic modulus is smaller than the first elastic modulus and the
third elastic modulus is greater than the second elastic modulus,
or (ii) the second elastic modulus is greater than the first
elastic modulus and the third elastic modulus is greater than the
second elastic modulus, or (iii) the second elastic modulus is
smaller than the first elastic modulus and third elastic modulus
smaller than the second elastic modulus.
11. A cover window comprising the multilayer polymer film of claim
1 and a layer of a transparent material, wherein the layer of a
transparent material has a speed of sound of at least 2000 m/s.
12. The cover window of claim 11, wherein the transparent material
is selected from the group consisting of polyimide, polyamide
imide, poly(methyl methacrylate), polyether ketone, polystyrene,
polycarbonate, polyester and particle reinforced polymer.
13. The cover window of claim 11, further comprising an additional
layer of a transparent material with a speed of sound of at least
2000 m/s, such that the multilayer polymer film is positioned
between the two layers of transparent material with a speed of
sound of at least 2000 m/s.
14. The cover window of claim 11 further comprising an adhesive
layer.
15. The cover window of claim 11, wherein a minimum Mode I
interlaminar fracture toughness (G.sub.lc) between any adjacent
layers in the cover window is at least 100 J/m.sup.2.
16. The cover window of claim 11, wherein the cover window has a
haze of less than 2%.
17. The cover window of claim 11, wherein the cover window has a b*
of less than 2.
18. The cover window of claim 11, wherein the cover window has a
transmittance of at least 80%.
19. An electronic device comprising the cover window of claim 11.
Description
FIELD OF THE DISCLOSURE
[0001] This invention is directed to multilayer polymer films,
cover windows and electronic devices.
BACKGROUND OF THE DISCLOSURE
[0002] There is increasing interest in creating foldable OLED
displays to be used in foldable smart phones, small tablets,
rollable phones and rollable large display formats for singly and
doubly curved displays for such uses as automotive panels and
appliance panels.
[0003] Polyimide films that contain aromatic monomers are typically
very thermally stable and are foldable. In addition to optical
requirements, flexibility requirements, surface damage resistance
and folding endurance requirements, a cover window must provide
severe impact endurance. Like rigid glass that can shatter or
withstand an impact wave, a polymer will transmit impact energy via
sound waves emanating from the impact directly onto the display. If
the impact energy is low, the display will remain intact. As the
impact energy increases, the display could suffer damage, at worst,
damaging the underlying electronic components and rendering the
display useless.
[0004] A film construction that can protect the display electronic
components from a sharp impact and does not suffer from
delamination will be important for flexible displays for portable
electronics.
SUMMARY
[0005] In a first aspect, a multilayer polymer film includes a
first substantially transparent polymer layer having a first
elastic modulus and a second substantially transparent polymer
layer having a second elastic modulus. The first elastic modulus is
different from the second elastic modulus and the first and second
substantially transparent polymer layers are bonded by
consolidation.
[0006] In a second aspect, a cover window includes the multilayer
polymer film of the first aspect and a layer of a transparent
material. The layer of a transparent material has a speed of sound
of at least 2000 m/s.
[0007] In a third aspect, an electronic device includes the cover
window of the second aspect.
DETAILED DESCRIPTION
[0008] In a first aspect, a multilayer polymer film includes a
first substantially transparent polymer layer having a first
elastic modulus and a second substantially transparent polymer
layer having a second elastic modulus. The first elastic modulus is
different from the second elastic modulus and the first and second
substantially transparent polymer layers are bonded by
consolidation.
[0009] In one embodiment of the first aspect, a Mode I interlaminar
fracture toughness (G.sub.lc) between the first and second
substantially transparent polymer layers is at least 500
J/m.sup.2.
[0010] In another embodiment of the first aspect, a difference
between the elastic moduli of the first and second substantially
transparent polymer layers is at least 5%.
[0011] In still another embodiment of the first aspect, the first
substantially transparent polymer layer, the second substantially
transparent polymer layer, or both the first and second
substantially transparent polymer layers have a speed of sound of
at least 1300 m/s.
[0012] In yet another embodiment of the first aspect, the first
substantially transparent polymer layer, the second substantially
transparent polymer layer, or both the first and second
substantially transparent polymer layers further include sub-micron
fillers.
[0013] In still yet another embodiment of the first aspect, the
polymer of the first substantially transparent polymer layer is
cross-linked, the polymer of the second substantially transparent
polymer layer is cross-linked, or the polymers of both the first
and second substantially transparent polymer layers are
cross-linked.
[0014] In a further embodiment of the first aspect, the first
substantially transparent polymer layer, the second substantially
transparent polymer layer, or both the first and second
substantially transparent polymer layers include a polyimide, a
polyamide imide, a block copolymer of a polyimide or a block
copolymer of a polyamide imide. In a specific embodiment, the first
substantially transparent polymer layer, the second substantially
transparent polymer layer, or both the first and second
substantially transparent polymer layers further include an
imidization catalyst.
[0015] In still a further embodiment of the first aspect, the
multilayer polymer film further includes a third substantially
transparent polymer layer having a third elastic modulus. The
second substantially transparent polymer layer is positioned
between the first and third substantially transparent polymer
layers, and the second and third substantially transparent polymer
layers are bonded by consolidation. In a specific embodiment, the
second elastic modulus is smaller than the first elastic modulus
and the third elastic modulus is greater than the second elastic
modulus, or the second elastic modulus is greater than the first
elastic modulus and the third elastic modulus is greater than the
second elastic modulus, or the second elastic modulus is smaller
than the first elastic modulus and third elastic modulus smaller
than the second elastic modulus.
[0016] In a second aspect, a cover window includes the multilayer
polymer film of the first aspect and a layer of a transparent
material. The layer of a transparent material has a speed of sound
of at least 2000 m/s.
[0017] In one embodiment of the second aspect, the transparent
material is selected from the group consisting of polyimide,
polyamide imide, poly(methyl methacrylate), polyether ketone,
polystyrene, polycarbonate, polyester and particle reinforced
polymer.
[0018] In another embodiment of the second aspect, the cover window
of further includes an additional layer of a transparent material
with a speed of sound of at least 2000 m/s, such that the
multilayer polymer film is positioned between the two layers of
transparent material with a speed of sound of at least 2000
m/s.
[0019] In still another embodiment of the second aspect, the cover
window of further includes an adhesive layer.
[0020] In yet another embodiment of the second aspect, a minimum
Mode I interlaminar fracture toughness (G.sub.lc) between any
adjacent layers in the cover window is at least 100 J/m.sup.2.
[0021] In still yet another embodiment of the second aspect, the
cover window has a haze of less than 2%.
[0022] In a further embodiment of the second aspect, the cover
window has a b* of less than 2.
[0023] In still a further embodiment of the second aspect, the
cover window has a transmittance of at least 80%.
[0024] In a third aspect, an electronic device includes the cover
window of the second aspect.
[0025] Multilayer polymer films can be used to form substantially
transparent and foldable films. In one embodiment, a multilayer
polymer film can include layers based on the same or different
polymer compositions that are bonded together by consolidation. In
one embodiment, useful polymer compositions for a multilayer
polymer can include polyimides, polyamide imides, poly(methyl
methacrylates), polyether ketones, polystyrenes, polycarbonates and
polyesters. Polyimides that contain aromatic monomers are typically
very thermally stable and are foldable.
[0026] In one embodiment, a multilayer polymer film can include
layers of block copolymers, such as polyimide block copolymers or
polyamide imide block copolymers. Compositions of block copolymers
typically are stiffer, i.e., have a higher elastic modulus, than
random copolymers of the same composition. For example, a block
copolymer of a polyimide can have a longer or higher molecular
weight block containing a combination of a more rigid dianhydride
and/or a more rigid diamine. In this way, the mechanical properties
of the block copolymer can be manipulated relative to the other
layers in the multilayer film. In one embodiment, a block copolymer
of polyimides will be used for a layer requiring a higher elastic
modulus and a polyimide will be used for a layer with a lower
elastic modulus.
[0027] Polyamide imide compositions typically are stiffer, i.e.,
have a higher elastic modulus, than polyimide compositions. In one
embodiment, a polyamide imide will be used for a layer requiring a
higher elastic modulus and a polyimide will be used for a layer
with a lower elastic modulus.
[0028] In one embodiment, the elastic modulus of a polymer layer
can be increased by the presence of sub-micron fillers. In another
embodiment, the elastic modulus of a polymer layer can be increased
by cross-linking between the polymer chains in the polymer layer.
In still another embodiment, the elastic modulus of a polyimide
layer or a polyamide imide layer can be increased by the
introduction of an imidization catalyst into the layer.
[0029] There are various embodiments of a multilayer polymer film
with different numbers of layers and variations on the relative
elastic moduli of the layers
[0030] In one embodiment, there are three polymer layers, the first
layer having a first elastic modulus, the second layer having a
second elastic modulus, and the third layer having a third elastic
modulus, wherein the second layer is positioned between the first
layer and the third layer.
[0031] In one three-polymer layer embodiment, the second elastic
modulus is smaller than the first elastic modulus and the third
elastic modulus is greater than the second elastic modulus. In one
such embodiment, the first elastic modulus has been increased by
the presence of sub-micron fillers in the first polymer layer, by
cross-linking between the polymer chains in the first polymer
layer, by the introduction of an imidization catalyst into the
first polymer layer, or by a combination thereof. Alternatively, in
other embodiments, the first polymer layer is a polyamide imide
layer or a layer of block copolymer of polyimides, and the second
polymer layer is a polyimide. In another such embodiment, the
elastic modulus of the third polyimide layer has been increased by
the presence of sub-micron fillers in the third polymer layer, by
cross-linking between the polymer chains in the third polymer
layer, by the introduction of an imidization catalyst into the
third polymer layer, or by a combination thereof. Alternatively, in
other embodiments, the third polymer layer is a polyamide imide
layer or a layer of block copolymer of polyimides. In still another
such embodiment, the first elastic modulus and the third elastic
modulus are essentially the same. In still another such embodiment,
the first elastic modulus is greater than the third elastic
modulus.
[0032] In another three-polymer layer embodiment, the second
elastic modulus is smaller than the first elastic modulus and the
third elastic modulus is smaller than the second elastic modulus.
In one such embodiment, the first elastic modulus has been
increased by the presence of sub-micron fillers in the first
polymer layer, by cross-linking between the polymer chains in the
first polymer layer, by the introduction of an imidization catalyst
into the first polymer layer, or by a combination thereof.
Alternatively, in other embodiments, the first polymer layer can be
a polyamide imide layer or a layer of block copolymer of
polyimides.
[0033] In still another three-polymer layer embodiment, the second
elastic modulus is greater than the first elastic modulus and the
third elastic modulus is greater than the second elastic modulus.
In one such embodiment, the third elastic modulus has been
increased by the presence of sub-micron fillers in the third
polymer layer, by cross-linking between the polymer chains in the
third polymer layer, by the introduction of an imidization catalyst
into the third polymer layer, when it includes a polyimide, or by a
combination thereof. Alternatively, in other embodiments, the third
polyimide layer can be a polyamide imide layer or a layer of block
copolymer of polyimides.
[0034] In another embodiment, there are four polymer layers, the
first layer having a first elastic modulus, the second layer having
a second elastic modulus, the third layer having a third elastic
modulus, and the fourth layer a fourth elastic modulus, wherein the
second layer is positioned between the first layer and the third
layer and the third layer is positioned between the second layer
and the fourth layer.
[0035] In one four-polymer layer embodiment, the second elastic
modulus is smaller than the first elastic modulus, the third
elastic modulus is smaller than the second elastic modulus, and the
fourth elastic modulus is larger than the third elastic modulus. In
one such embodiment, the first elastic modulus has been increased
as described above for the three-polymer layer embodiments. In
another such embodiment, the second elastic modulus has been
increased as described above for the three-polymer layer
embodiments. In yet another such embodiment, the fourth elastic
modulus has been increased as described above for the three-polymer
layer embodiments. In still another such embodiment, the second
elastic modulus and the fourth elastic modulus are essentially the
same. In an additional embodiment, the second elastic modulus is
larger than the fourth elastic modulus.
[0036] In another four-polymer layer embodiment, the second elastic
modulus is smaller than the first elastic modulus, the third
elastic modulus is smaller than the second elastic modulus, and the
fourth elastic modulus is smaller than the third elastic
modulus.
[0037] In still another four-polymer layer embodiment, the second
elastic modulus is smaller than the first elastic modulus, the
third elastic modulus is greater than the second elastic modulus,
and the fourth layer has a low glass transition temperature and the
fourth elastic modulus is smaller than the elastic modulus of any
of the other three layers. In still another such embodiment, the
first elastic modulus and the third elastic modulus are essentially
the same. In an additional such embodiment, the first elastic
modulus is larger than the third elastic modulus.
[0038] In still another embodiment, there are five polymer layers,
the first layer having a first elastic modulus, the second layer
having a second elastic modulus, the third layer having a third
elastic modulus, the fourth layer a fourth elastic modulus, and the
fifth layer having a fifth elastic modulus, wherein the second
layer is positioned between the first layer and the third layer,
the third layer is positioned between the second layer and the
fourth layer and the fourth layer is positioned between the third
layer and the fifth layer.
[0039] In one five-polymer layer embodiment, the second elastic
modulus is smaller than the first elastic modulus, the third
elastic modulus is smaller than the second elastic modulus, the
fourth elastic modulus is greater than the third elastic modulus,
and the fifth layer has a low glass transition temperature and a
fifth elastic modulus smaller than the elastic modulus of any of
the other four layers and wherein the first elastic modulus is
greater than the elastic modulus of any of the other four layers.
In one such embodiment, the elastic modulus of the first polymer
layer has been increased as described above for the three-polymer
layer embodiments. In another such embodiment, the second elastic
modulus and the fourth elastic modulus are essentially the same. In
still another such embodiment, the second elastic modulus is
greater than the fourth elastic modulus.
[0040] In another five-polymer layer embodiment, the second elastic
modulus is smaller than the first elastic modulus, the third
elastic modulus is smaller than the second elastic modulus, the
fourth elastic modulus is smaller than the third elastic modulus,
and the fifth layer has a low glass transition temperature and a
fifth elastic modulus smaller than the elastic modulus of any of
the other four layers and wherein the first elastic modulus is
greater than the elastic modulus of any of the other four layers.
In one such embodiment, the elastic modulus of the first polymer
layer has been increased as described above for the three-polymer
layer embodiments.
[0041] In still another five-polymer layer embodiment, the second
elastic modulus is smaller than the first elastic modulus, the
third elastic modulus is greater than the second elastic modulus,
the fourth elastic modulus is greater than the elastic modulus of
any of the other four layers, and the fifth layer has a low glass
transition temperature and a fifth elastic modulus smaller than the
elastic modulus of any of the other four layers. In another such
embodiment, the first elastic modulus and the third elastic modulus
are essentially the same. In still another such embodiment, the
first elastic modulus is greater than the third elastic
modulus.
[0042] In another five-polymer layer embodiment, the second elastic
modulus is smaller than the first elastic modulus, the third
elastic modulus is smaller than the second elastic modulus, the
fourth elastic modulus is greater than the elastic modulus of any
of the other four layers, and the fifth layer has a low glass
transition temperature and a fifth elastic modulus smaller than the
elastic modulus of any of the other four layers. Those skilled in
the art will understand how to form multilayer polymer films bonded
by consolidation having any number of layers and how to control the
relative elastic moduli of each layer.
[0043] In one embodiment, a difference between the elastic moduli
of two adjacent substantially transparent polymer layers is at
least 5, at least 15 or at least 25%.
[0044] Even when using the same polyimide and the same amount of
sub-micron fillers, the same degree of cross-linking, the same
amount of imidization catalyst, the same block copolymer of
polyimides, or the same polyamide imide, it is difficult to produce
two layers with exactly identical elastic moduli. "Essentially
identical" is used herein to describe those layers prepared with
the intent and care to have the same elastic moduli.
[0045] Various other layers in the configurations described above
may also have the elastic modulus increased by the presence of
sub-micron fillers, by cross-linking between polymer chains, by the
introduction of an imidization catalyst, or by a combination
thereof.
[0046] In one embodiment, a multilayer polymer film is
substantially transparent. Transparency or transmittance in the
visible (400-700 nm) or between 380 and 780 nm is necessary. A
substantially transparent polymer film or layer can have a
transmittance of greater than 60, 70, 80 or 90% in the visible
range.
[0047] In one embodiment, the polymer films must be colorless and
transparent. Transparency or high transmittance in the visible
spectrum (400-700 nm), or between 380 and 780 nm, is necessary.
Typical specifications require that both a* and b* are no greater
than 1 color unit from neutral (0) in CIE L*, a*, b* color space
coordinates. The three coordinates of CIE L*, a*, b* represent: (1)
the lightness of the color (L*=0 yields black and L*=100 indicates
diffuse white), (2) its position between red/magenta and green
(negative a* values indicate green, while positive values indicate
magenta) and (3) its position between yellow and blue (negative b*
values indicate blue and positive values indicate yellow). For a 50
.mu.m film, the absolute value of a* and b* should each be less
than 2, or less than 1.
[0048] The polyimides, polyamide imides and block copolymers of
polyimides are described in terms of the diamines and dianhydrides
used to form them.
[0049] Examples of suitable diamines to form the polyimide,
polyamide imide and block copolymer of polyimide layers include
p-phenylenediamine (PPD), m-phenylenediamine (MPD),
2,5-dimethyl-1,4-diaminobenzene, 2,5-dimethyl-1,4-phenylenediamine
(DPX), 2,2-bis-(4-aminophenyl) propane,
1,4-naphthalenediamine,1,5-naphthalenediamine,
4,4'-diaminobiphenyl, 4,4''-diamino terphenyl, 4,4'-diamino
benzanilide, 4,4'-diaminophenyl benzoate, 4,4'-diaminobenzophenone,
4,4'-diaminodiphenylmethane (MDA), 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), 4,4'-diaminodiphenyl ether
(ODA), 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, 1,5-diaminonaphthalene,
3,3'-dimethyl-4,4'-diaminobiphenyl, m-amino benzoyl-p-amino
anilide, 4-aminophenyl-3-aminobenzoate, N,N-bis-(4-aminophenyl)
aniline, 2,4-diaminotoluene, 2,5-diaminotoluene,
2,6-diaminotoluene, 2,4-diamine-5-chlorotoluene,
2,4-diamine-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, and
p-xylylene diamine.
[0050] Other useful diamines include
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-phenoxy aniline) isopropylidene,
2,4,6-trimethyl-1,3-diaminobenzene,
2,4,6-trimethyl-1,3-diaminobenzene.
[0051] In one embodiment, a suitable diamine can include a
fluorinated diamine, such as 2,2'-bis(trifluoromethyl) benzidine
(TFMB), trifluoromethyl-2,4-diaminobenzene,
trifluoromethyl-3,5-diaminobenzene,
2,2'-bis-(4-aminophenyl)-hexafluoro propane,
4,4'-diamino-2,2'-trifluoromethyl diphenyloxide,
3,3'-diamino-5,5'-trifluoromethyl diphenyloxide,
9.9'-bis(4-aminophenyl)fluorene,
4,4'-trifluoromethyl-2,2'-diaminobiphenyl,
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'-sulfoxyl-bis-[(3-trifluoromethyl)benzene amine],
4,4'-keto-bis-[(2-trifluoromethyl)benzene amine],
1,1-bis[4'-(4''-amino-2''-trifluoromethylphenoxy)phenyl]cyclopentane,
1,1-bis[4'-(4''-amino-2''-trifluoromethylphenoxy)phenyl]cyclohexane,
2-trifluoromethyl-4,4'-diaminodiphenyl ether;
1,4-(2'-trifluoromethyl-4',4''-diaminodiphenoxy)-benzene,
1,4-bis(4'-aminophenoxy)-2-[(3',5'-ditrifluoromethyl)phenyl]benzene,
1,4-bis[2'-cyano-3'(''4-amino
phenoxy)phenoxy]-2-[(3',5'-ditrifluoro-methyl)phenyl]benzene
(6FC-diamine),
3,5-diamino-4-methyl-2',3',5',6'-tetrafluoro-4'-tri-fluoromethyldiphenylo-
xide,
2,2-Bis[4'(4''-aminophenoxy)phenyl]phthalein-3',5'-bis(trifluorometh-
yl)anilide (6FADAP) and
3,3',5,5'-tetrafluoro-4,4'-diamino-diphenylmethane (TFDAM). In a
specific embodiment, the fluorinated diamine is
2,2'-bis(trifluoromethyl) benzidine (TFMB).
[0052] In one embodiment, any number of suitable dianhydrides can
be used. The dianhydrides can be used in their tetra-acid form (or
as mono, di, tri, or tetra esters of the tetra acid), or as their
diester acid halides (chlorides). However, in some embodiments, the
dianhydride form can be preferred, because it is generally more
reactive than the acid or the ester.
[0053] Examples of suitable dianhydrides include 3,3',4,4'-biphenyl
tetracarboxylic dianhydride (BPDA), 1,2,5,6-naphthalene
tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic
dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride,
2-(3',4'-dicarboxyphenyl) 5,6-dicarboxybenzimidazole dianhydride,
2-(3',4'-dicarboxyphenyl) 5,6-dicarboxybenzoxazole dianhydride,
2-(3',4'-dicarboxyphenyl) 5,6-dicarboxybenzothiazole dianhydride,
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,
bicyclo-[2,2,2]-octen-(7)-2,3,5,6-tetracarboxylic-2,3,5,6-dianhydride,
4,4'-thio-diphthalic anhydride, bis (3,4-dicarboxyphenyl) sulfone
dianhydride, bis (3,4-dicarboxyphenyl) sulfoxide dianhydride
(DSDA), bis (3,4-dicarboxyphenyl oxadiazole-1,3,4) p-phenylene
dianhydride, bis (3,4-dicarboxyphenyl) 2,5-oxadiazole
1,3,4-dianhydride, bis 2,5-(3',4'-dicarboxydiphenylether)
1,3,4-oxadiazole dianhydride, 4,4'-oxydiphthalic anhydride (ODPA),
bis (3,4-dicarboxyphenyl) thio ether dianhydride, bisphenol A
dianhydride (BPADA), bisphenol S dianhydride,
bis-1,3-isobenzofurandione, 1,4-bis(4,4'-oxyphthalic anhydride)
benzene, bis (3,4-dicarboxyphenyl) methane dianhydride,
cyclopentadienyl tetracarboxylic acid dianhydride, cyclopentane
tetracarboxylic dianhydride, ethylene tetracarboxylic acid
dianhydride, perylene 3,4,9,10-tetracarboxylic dianhydride,
pyromellitic dianhydride (PMDA), tetrahydrofuran tetracarboxylic
dianhydride, 1,3-bis-(4,4'-oxydiphthalic anhydride) benzene,
2,2-bis(3,4-dicarboxyphenyl) propane dianhydride,
2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,
2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,
2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,
phenanthrene-1,8,9,10-tetracarboxylic dianhydride,
pyrazine-2,3,5,6-tetracarboxylic dianhydride,
benzene-1,2,3,4-tetracarboxylic dianhydride,
thiophene-2,3,4,5-tetracarboxylic dianhydride and cyclobutane
dianhydride (CBDA).
[0054] In one embodiment, a suitable dianhydride can include a
fluorinated dianhydride, such as
4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and
9,9-bis (trifuoromethyl)-2,3,6,7-xanthene tetracarboxylic
dianhydride. In a specific embodiment, the fluorinated dianhydride
is 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA).
[0055] In specific embodiments, 6FDA/TFMB and BPDA/6FDA//TFMB
polymer layers were used to form multilayers. In one embodiment, a
poly(amic acid) blend containing BPDA, 6FDA and TFMB was created by
polymerizing BPDA with TFMB and combining with a polyamic acid
derived from the reaction of 6FDA with TFMB.
[0056] In one embodiment, the elastic modulus of a polymer layer
can be increased by the presence of sub-micron fillers. The percent
transmittance of the multilayer film will be a function of the
refractive index difference between the filler and the polymer host
and the size of the filler. Smaller differences in the refractive
index between the filler and the polymer host will allow for larger
dimensions of the filler without adversely affecting the
transmittance of the film. The sub-micron filler can be inorganic
or organic and can be present in an amount between and optionally
including any two of the following percentages: 5, 10, 15, 20, 25,
30, 35, 40, and 45 volume percent of the polymer film.
[0057] Depending on the refractive index of the filler, in one
embodiment the sub-micron filler can have a size of less than 550
nm in at least one dimension. In other embodiments, the filler can
have a size of less than 500, less than 450, less than 400, less
than 350, less than 300, less than 250, or less than 200 nm (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). The average aspect ratio of the filler can be 1 or
greater. In some embodiments, the sub-micron filler is selected
from a group consisting of needle-like fillers (acicular), fibrous
fillers, platelet fillers, polymer fibers, and mixtures thereof. In
one embodiment, the sub-micron filler is substantially
non-aggregated. The sub-micron filler can be hollow, porous, or
solid. In one embodiment, the sub-micron fillers of the present
disclosure exhibit an aspect ratio of at least 1, at least 2, at
least 4, at least 6, at least 8, at least 10, at least 12, or at
least 15 to 1.
[0058] In some embodiments, sub-micron fillers are 100 nm in size
or less. In some embodiments, the fillers are spherical or oblong
in shape and are nanoparticles. In one embodiment, sub-micron
fillers can include inorganic oxides, such as oxides of silicon,
aluminum and titanium, hollow (porous) silicon oxide, antimony
oxide, zirconium oxide, indium tin oxide, antimony tin oxide, mixed
titanium/tin/zirconium oxides, and binary, ternary, quaternary and
higher order composite oxides of one or more cations selected from
silicon, titanium, aluminum, antimony, zirconium, indium, tin,
zinc, niobium and tantalum. In one embodiment, nanoparticle
composites (e.g. single or multiple core/shell structures) can be
used, in which one oxide encapsulates another oxide in one
particle.
[0059] In one embodiment, sub-micron fillers can include other
ceramic compounds, such as boron nitride, aluminum nitride, ternary
or higher order compounds containing boron, aluminum and nitrogen,
gallium nitride, silicon nitride, aluminum nitride, zinc selenide,
zinc sulfide, zinc telluride, silicon carbide, and their
combinations, or higher order compounds containing multiple cations
and multiple anions.
[0060] In one embodiment, solid silicon oxide nanoparticles can be
produced from sols of silicon oxides (e.g., colloidal dispersions
of solid silicon oxide nanoparticles in liquid media), especially
sols of amorphous, semi-crystalline, and/or crystalline silica.
Such sols can be prepared by a variety of techniques and in a
variety of forms, which include hydrosols (i.e., where water serves
as the liquid medium), organosols (i.e., where organic liquids
serves as the liquid medium), and mixed sols (i.e., where the
liquid medium comprises both water and an organic liquid). See,
e.g., descriptions of the techniques and forms disclosed in U.S.
Pat. Nos. 2,801,185, 4,522,958 and 5,648,407. In one embodiment,
the nanoparticle is suspended in a polar, aprotic solvent, such as,
DMAC or other solvent compatible with polyamic acid or poly(amide
amic acid). In another embodiment, solid nanosilica particles can
be commercially obtained as colloidal dispersions or sols dispersed
in polar aprotic solvents, such as for example DMAC-ST (Nissan
Chemical America Corporation, Houston Tex.), a solid silica colloid
in dimethylacetamide containing less than 0.5 percent water, with
20-21 wt % SiO.sub.2, with a median nanosilica particle diameter
d50 of about 16 nm.
[0061] In one embodiment, sub-micron fillers can be porous and can
have pores of any shape. One example is where the pore comprises a
void of lower density and low refractive index (e.g., a void
containing air) formed within a shell of an oxide such as silicon
oxide, i.e., a hollow silicon oxide nanoparticle. The thickness of
the sub-micron fillers shell affects the strength of the sub-micron
fillers. As the hollow silicon oxide particle is rendered to have
reduced refractive index and increased porosity, the thickness of
the shell decreases resulting in a decrease in the strength (i.e.,
fracture resistance) of the sub-micron fillers. Methods for
producing such hollow silicon oxide nanoparticles are known, for
example, as described in Japanese Patent Nos. 4406921B2 and
4031624B2. Hollow silicon oxide nanoparticles can be obtained from
JGC Catalysts and Chemicals, LTD, Japan.
[0062] In one embodiment, sub-micron fillers can be coated with a
coupling agent. For example, a nanoparticle can be coated with an
aminosilane, phenylsilane, acrylic or methacrylic coupling agents
derived from the corresponding alkoxysilanes. Trimethylsilyl
surface capping agents can be introduced to the nanoparticle
surface by reaction of the sub-micron fillers with
hexamethyldisilazane. In one embodiment, sub-micron fillers can be
coated with a dispersant. In one embodiment, sub-micron fillers can
be coated with a combination of a coupling agent and a dispersant.
Alternatively, the coupling agent, dispersant or a combination
thereof can be incorporated directly into the polyimide film and
not necessarily coated onto the sub-micron fillers.
[0063] The surface coating on an inorganic sub-micron filler will
affect its refractive index. The refractive index of sub-micron
fillers with a surface coating can be estimated by summing the
volume fraction of the surface coating multiplied by its refractive
index and the volume fraction of the inorganic core multiplied by
the refractive index of the core.
[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. In one embodiment, for a multilayer
polymer film with outer layers on both sides of a core layer, the
outer layer modulus can be increased while maintaining a softer
core layer. Since there is some interdiffusion between layers, the
boundary layers where there is intermixing between layers can
extend over a distance of 1-2 .mu.m or greater so that the
transition in properties between adjacent layers are more
gradual.
[0065] In one embodiment, the elastic modulus of a polymer layer
can be increased by cross-linking between the polymer chains within
the layer. The cross-linking chemistry is targeted within specific
layers in which a higher elastic modulus and speed of sound is
required. Cross-linking between the polymer chains can be achieved
through thermal processing or through UV initiated chemistries.
[0066] Thermally induced cross-linking between the polymer chains
can be achieved by introducing diacetylene groups into the polymer
composition. These acetylene or ethylene groups can be cross-linked
with other acetylene or ethylene groups, in some cases by thermally
activated processes near the temperature of imidization of the
film. Other approaches for thermally initiated cross-linking
include the inclusion of monomers with carboxylic acid pendant
groups that can decarboxylate at moderate temperatures to generate
radicals that can react and form covalent bonds with entities on a
neighboring polymer chain. An example of such a monomer which can
be co-polymerized into the polyamic acid is 3,5 diaminobenzoic
acid, which would generate an aryl radical to initiate
cross-linking reactions.
[0067] Cross-linking chemistry between polymer chains can also be
achieved through the incorporation of diols into the polymer
backbone. One such example is 1,4-butylene glycol. In addition, the
diols can react with carboxylic acid moieties on neighboring chains
(such as those introduced by diaminobenzoic acid) to form an ester
linkage between polymer chains.
[0068] UV induced cross-linking reactions can also be used, and
these may be performed before or after the thermal imidization
step. One approach would be to incorporate DAM
(2,4,6-trimethl-1,3-phenylene diamine) into the polymer backbone
during the formation of the polyamic acid along with a benzophenone
monomer such as BTDA (3',4,4'-benzophenonoetetracarboxylic
dianhdride). It is postulated that the benzophenone can react with
hydrogen donating moieties on a neighboring chain (such as those on
the DAM monomer or another monomer with pendant hydrogen groups)
through hydrogen abstraction and subsequent radical coupling
between the polymer chains.
[0069] Cross-linking and branching between polymer chains can also
be achieved by introducing trifunctional monomers (e.g. triamines)
into the polymer backbone.
[0070] The cross-linking chemistry has a beneficial impact on the
interlayer bonding. For instance, if two chemical moieties are
needed for the cross-link, one could be used for the polymer
composition in each layer. A thermally or UV induced cross-linking
reaction can improve the bonding between layers by introducing
covalent bonds between polymer chains of two neighboring layers.
When incorporating cross-linking in any polymer layers of the
multilayer polymer film, the layers are first bonded by
consolidation, followed by cross-linking.
[0071] In one embodiment, polyimide layer properties can be
adjusted by the introduction of imidization catalysts into specific
layers. In general, the catalyst will lower the temperature of
imidization, increase the crystallinity and increase the polyimide
modulus. The concentration and type of catalyst can be used to
control properties. Typical imidization catalysts can range from
bases such as imidazole, 1-methylimidazole, 2-methylimidazole,
1,2-dimethylimidazole, 2-phenylimidazole, benzimidazole,
isoquinoline, or substituted pyridines such as methyl pyridines,
lutidine, and trialkylamines. Combinations of the tertiary amines
with acid anhydrides can be used. These dehydration agents, which
can act as co-catalysts, include acetic anhydride, propionic
anhydride, n-butyric anhydride, benzoic anhydride and others. The
ratio of these catalysts and their concentration in the polyamic
acid layer will influence imidization kinetics and the film
properties. Some configurations may have different catalysts
introduced into different layers, depending on the properties
desired. For instance, for a three-layer polyimide film where the
first and third layers possess an increased modulus, the catalysts
can be introduced only into those two layers.
[0072] Since there is some interdiffusion of solvents between
layers, the imidization catalyst can also interdiffuse to some
degree as well. This will depend on the catalyst concentration, the
thickness of the layers, and the drying profile used to prepare the
film. In this way, a property gradation from one layer to another
can be achieved.
[0073] Adjacent polymer layers of the multilayer polymer film are
bonded by consolidation. Consolidation is a welding process rather
than an adhesion process. The layers to be consolidated or welded
must be capable of undergoing a physical change--melting and
solidification. There is heat transfer to soften and melt the
layers to be consolidated together. The surfaces are brought
together and allowed to accomplish intimate molecular contact.
There is polymer interdiffusion by reptation (snake-like) motion.
This accomplishes strong bonds as the long polymer chains move
across the interface of the two layers to be consolidated. It is
common for the reconsolidated interface to be undetectable.
[0074] In this process, the polyamic or polyimide amic acids are
either cast as polyamic acid layers, partially imidized polyamic
layers, polyamide amic acids, soluble polyimides or soluble
polyamide imides. These layers can be cast in a co-extrusion
process that results in consolidation. In this process, the
polyamic acid polymer chains can co-mingle; there can be
co-entanglement of the polyamic or polyimide amic acids layers,
partially imidized polyamic layers, polyimide amic acids, soluble
polyimide or soluble polyamide imides chains between neighboring
layers as discussed above. There will be greater interlayer bonding
than can be conventionally achieved by coating one formulation onto
a second pre-formed polymer substrate. When the multi-layer is
based on polyamic acid, it can be imidized in a separate step, so
that the entire multilayer is cured or imidized simultaneously. If
the material is co-extruded using a multicavity die with
independent polyamic acid streams, there is also a significant
manufacturing cost advantage, because the layers are formed and
combined in a single or cascaded casting process (as opposed to
sequentially coating one film layer on top of the other). In one
embodiment, multiple slot dies can be slightly cascaded.
[0075] In one embodiment, the multilayer polymer film is prepared
by simultaneously extruding the layers. In some embodiments, the
layers are extruded through a single or multi-cavity extrusion die.
In one embodiment, the multilayer film is produced using a
single-cavity die. If a single-cavity die is used, the laminar flow
of the streams should be of high enough viscosity to prevent
comingling of the streams and to provide even layering. In one
embodiments, the multilayer polymer film is prepared by casting
from a slot die onto a moving stainless-steel belt. In a specific
embodiment including a polyimide layer(s), the belt is then passed
through a convective oven, to evaporate solvent and partially
imidize the polymer, to produce a "green" film. The green film can
be stripped off the casting belt and wound up. The green film can
then be passed through a tenter oven to fully cure the polyimide.
In some embodiments, during tentering, shrinkage can be minimized
by constraining the film along the edges (i.e. using clips or
pins).
[0076] In some embodiments, layers can be formed by successive
coatings of the polyamic acid, polyamic imide, soluble polyimide,
or soluble polyamide imides. For instance, solutions of these
polymers can be sequentially deposited by slot die coating,
casting, or similar processes.
[0077] In one embodiment, outer layers of a multilayer polymer film
can be applied to a core layer or during an intermediate
manufacturing stage of film formation, such as to gel film or to
green film.
[0078] Also provided is a cover window for a display comprising a
multilayer polymer film of the invention. The first layer of each
of the various multilayer variations is the layer farthest from the
display.
[0079] In an impact resistance structure such as the cover window,
the velocity at which stresses propagate in a material must be high
to allow dissipation of the initial kinetic energy over a large
volume of the structure, and to enhance the interchange of momentum
between an impactor and the target. Sound, a mechanical wave, and
stresses propagate at various wave speeds in a material. Different
modes of deformation result in different waves speeds
(longitudinal, distortional, rayleigh, etc.) in a material.
[0080] Herein reference to the high speed of sound layer means the
speed of the longitudinal wave in the material. This is the fastest
elastic wave in a material. It is common to refer to the speed of
the longitudinal wave as the speed of sound in the material. For an
isotropic material, the longitudinal wave speed equation is
G lc - ( 1 v ) ( 1 v ) ( 1 2 v ) E .rho. ##EQU00001##
where,
[0081] E is the elastic modulus of the material
[0082] v is the Poisson's ratio of the material
[0083] .rho. is the density of the material
[0084] In an embodiment, the interfaces in the multilayer polymer
film have a Mode I interlaminar fracture toughness (G.sub.lc) of at
least 100, at least 500, at least 1500 or at least 3000 J/m.sup.2.
In one embodiment, a minimum Mode I interlaminar fracture toughness
(G.sub.lc) between any adjacent layers in a cover window is at
least 100, at least 200 or at least 350 J/m.sup.2. In one
embodiment, the speed of sound in at least one substantially
transparent layer of the multilayer polymer film is at least 1300,
at least 1800 or at least 2000 m/s.
[0085] In one embodiment, the cover window further comprises a
layer of transparent material with a high speed of sound positioned
between the multilayer polymer film and the display. In one such
embodiment, the speed of sound of the transparent material with a
high speed of sound is at least 2000, at least 2500 or at least
3000 m/s. In another such embodiment, the transparent material with
a high speed of sound polyimide, polyamide imide, poly(methyl
methacrylate), polyether ketone, polystyrene, polycarbonate or
polyester. In still another such embodiment, the transparent
material with a high speed of sound is a particle reinforced
polymer.
[0086] In another embodiment, the cover window further comprises a
layer of transparent material with a high speed of sound positioned
above the first layer of the multilayer polymer film. In one such
embodiment, the speed of sound of the transparent material with a
high speed of sound is at least 2000, at least 2500 or at least
3000 m/s. In another such embodiment, the transparent material with
a high speed of sound is polyimide, polyamide imide, poly(methyl
methacrylate), polyether ketone, polystyrene, polycarbonate or
polyester. In still another such embodiment, the transparent
material with a high speed of sound is a particle reinforced
polymer.
[0087] In another embodiment, the cover window further comprises
two layers of transparent material with a high speed of sound, one
layer positioned between the multilayer polymer film and the
display and one layer positioned above the first layer of the
multilayer polymer film. In one such embodiment, the speed of sound
of the transparent material with a high speed of sound is at least
2000, at least 2500 or at least 3000 m/s. In another such
embodiment, the transparent material with a high speed of sound is
polyimide, polyamide imide, poly(methyl methacrylate), polyether
ketone, polystyrene, polycarbonate or polyester. In still another
such embodiment, the transparent material with a high speed of
sound is a particle reinforced polymer.
[0088] In one embodiment, a cover window further comprises an
adhesive layer, such as an epoxy adhesive, an acrylic adhesive or a
urethane adhesive.
[0089] In one embodiment, a cover window can include more than one
multilayer polymer film. For instance, in one embodiment, a cover
window can include a first multilayer polymer film, a first
adhesive, a layer of transparent material with a high speed of
sound, a second adhesive and a second multilayer polymer film. In
another embodiment, a cover window can include a first layer of
transparent material with a high speed of sound, a first multilayer
polymer film, and second layer of transparent material with a high
speed of sound, an adhesive, a third layer of a transparent
material with a high speed of sound and a second multilayer polymer
film. Those skilled in the art will understand that any number of
cover window designs can be provided based on an understanding of
the properties of the different layers as described in the present
invention.
EXAMPLES
Test Methods
Elastic Modulus
[0090] The elastic modulus was measured using a nanoindenter
specially configured to measure the stiffness of films.
Nanoindentation measures a transverse modulus with some in-plane
modulus component, ideal for a thin film. A nanoindenter (Hysitron
TI 980 Tribolndenter, Bruker, Minneapolis, Minn.) was used to
characterize the film indentation modulus. The nanoindenter had
load and displacement resolutions of 1 nN and 0.04 nm,
respectively, and was operated in continuous stiffness mode whereby
the indenter tip was continuously oscillated at a 1-2 nm amplitude
for improved surface detection and extraction from a single
measurement of mechanical properties as a function of indentation
depth. A standard Berkovich tip whose projected contact area
function was calibrated to an indentation depth from .about.50 nm
and above by making 20 to 25 indentations on each specimen. The
indicated films were mounted on sample holders using an adhesive to
sample mounts. Indentations were made on each coating in at least
six different locations once the test system had reached a thermal
drift of .about.0.1-0.2 nm/sec. After measurements, subsequent to
the measurement, three to five indentations were again made on the
specimen to verify the previous calibration.
Interlaminar Fracture Toughness in Mode I (G.sub.lc)
[0091] Interfacial bond strength was measured with a
double-cantilever beam test. The test uses a 1''.times.6''
multilayer film specimen. This specimen was adhered top and bottom
with 1''.times.6'' aluminum backing bars to limit the sample
deflection under load, and to attach to loading blocks. The result
is a sandwich as follows: Al bar/`A` Layer/`B` layer/`A` layer/Al
bar. Then, loading blocks were attached to the aluminum backing
bars top and bottom. The samples were tested in an ElectroForce
1000 load frame equipped with a 1000 lb load cell. The test
purposefully creates an initial crack between the weakest layers
and propagates that crack along the interface while measuring the
transverse load, the opening displacement, and the crack length
along the specimen long axis. If the crack can be easily created,
the interfacial adhesion is low or modest and G.sub.lc can be
measured. If the crack cannot be created, the interlaminar adhesion
is high, or is not adhesion at all, but instead consolidation. A
fully consolidated tri-layer stack should not be able to be
separated. The locus of failure should be elsewhere.
Thickness
[0092] Cross-sectional scanning electron microscope (SEM) images of
films were obtained to determine the thicknesses of the multilayer
films and the individual film layers. Film samples were cut and
mounted in an epoxy and allowed to dry overnight. The samples were
then polished using a Buehler variable speed grinder/polisher and
placed into a desiccator for about two hours to ensure dryness.
Images were captured using a Hitachi S-3400 SEM (Hitachi High
Technologies America, Inc., Schaumburg, Ill.) under variable
pressure.
Example 1
[0093] For Example 1 (E1), multilayer films were cast by
co-extrusion to form `ABA` type layers by consolidation. Three
separate polyamic polymer streams were simultaneously extruded
through a multi-cavity extrusion die onto a heated moving belt to
form a co-extruded three-layer polyamic acid film that can be cured
to form a three-layer polyimide film. The thicknesses of the
polyimide core layer (second transparent, colorless polymer layer)
and the top and bottom outer layers (first and third transparent,
colorless polymer layers) were adjusted by varying the amounts of
polyamic acids fed to the extruder. Silicon oxide nanoparticles
were introduced into the outer `A` layers, to increase the layer
modulus.
[0094] To prepare the core layer (second transparent, colorless
polymer layer), in a nitrogen purged 80-gallon reactor, 16.20 kg of
trifluoromethyl-benzidine (TFMB, Seika Corporation, Wakayam Seika
Kogyo Co., LTD., Japan) and 143.34 kg of dimethyl acetamide (DMAC)
were stirred and agitated. 21.91 kg of
4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA, Synasia,
Metuchen, N.J.) were added in four separate aliquots over a 6 hours
period. The reaction mixture was maintained at .about.40.degree. C.
during this procedure. Eight additional aliquots of 36.145 g of
6FDA were added to the reaction mixture over a period of .about.3
hours. The viscosity of the pre-polymer was .about.60 poise.
[0095] A portion of the polymer was polymerized ("finished") to
.about.1200-1300 poise using a mixture of 6 wt % pyromellitic
dianhydride (PMDA) in DMAC in a nitrogen purged reactor. The
material was polymerized with the PMDA solution over the course of
.about.24 hours at 40.degree. C.
[0096] To prepare the outer polymer layers (first and third
transparent, colorless polymer layers), a portion of the polymer
used in the core layer was also co-extruded in the outer skin
layer. However, this layer was co-mingled with a stream of silicon
oxide nanoparticles. The silicon oxide nanocolloid was injected
into this outer layer. The colloid contains silicon oxide
nanoparticles which are .about.20-30 nm in diameter and are
colloidally dispersed at .about.31 wt % in DMAC. The product was
derived from a Ludox.RTM. TMA colloid silica product in water
(Sigma-Aldrich, St. Louis, Mo.). The colloid was deionized (Na ions
removed) by exchanging with Dowex.RTM. HCR-W2 resin (hydrogen form,
Sigma-Aldrich). The deionized Ludox.RTM. TMA was exchanged into
DMAC solvent by distillation. During the final part of the
exchange, a trimethoxy phenylsilane capping agent was introduced
into the colloid mixture to functionalize the nanoparticles. The
nanoparticle stream was introduced at the required volumetric rate
to create a silicon oxide nanoparticle enriched outer layer, with
.about.13 vol % SiO.sub.2 nanoparticles.
[0097] The multilayer polymer film was formed by co-extrusion. The
flow rates of the polyamic acid solutions were adjusted to yield a
three-layer co-extruded film, in which the outer layers were
.about.5-6 .mu.m after drying. The inner core layer was
.about.35-36 .mu.m. The extruded multilayer polymer film was dried
at an oven temperature in the range of from about 95 to about
150.degree. C. to produce a green film containing some DMAC
solvent.
[0098] The dried film was mounted on a 3.times.8-inch pin frame to
secure it and placed in a furnace (Thermolyne.TM. F6000 box
furnace, Thermo Fisher Scientific, Inc., Waltham, Mass.). The
furnace was nitrogen purged and heated according to the following
temperature protocol:
[0099] 25 to 45.degree. C. (5.degree. C./min), hold at 45.degree.
C. for 5 minutes;
[0100] 45 to 150.degree. C. (20.degree. C./min), hold at
150.degree. C. for 10 minutes;
[0101] 150 to 250.degree. C. (20.degree. C./min), hold at
250.degree. C. for 10 minutes;
[0102] 250 to 350.degree. C. (20.degree. C./min), hold at
350.degree. C. for 5 minutes.
[0103] The films were removed "hot" from the oven after heating to
350.degree. C. for 5 minutes and allowed to cool in air.
Example 2
[0104] For Example 2 (E2), the same procedures as described in E1
were used, except that the flow rate of the silicon oxide colloid
was increased to increase the concentration of silicon oxide
nanoparticles in the outer layers to .about.18 vol %.
[0105] High resolution microscopy was used to observe the
interfaces between the layers of the multilayer polymer films.
Films were prepared as described above in E1 and E2, except that
instead of curing the films in a furnace, self-supported films were
heated with radiant heaters in a tenter oven from about 180 to
about 620.degree. C. (radiant heater surface temperature) to
completely dry and imidized the polymers. Samples were prepared by
ultra-microtome to capture transmission electron microscopy (TEM)
cross-section images of the films. The transition regions from the
outer layers and the core is very gradual. Some silicon oxide
nanoparticles are present in this interface region, and there is no
clear boundary between the outer layers and the core layer. This
microstructure results in high adhesion between the outer and the
core layers due to bonding by consolidation.
[0106] In both E1 and E2, the nanoindentation modulus of the
unreinforced `B` layer was 4.53 GPa. In the case with the higher
level of particle reinforcement, the `A` layer measured 5.57 GPa
modulus, some 23% higher than the modulus of the `A` layer. In the
case with the lower level of particle reinforcement, the `A` layer
measured 5.46 GPa modulus, some 21% higher than the modulus of the
`A` layer (Table 1).
TABLE-US-00001 TABLE 1 Vol % SiO.sub.2 in Vol % SiO.sub.2 in Avg.
Modulus in Avg. Modulus Example Layers Layer A Layer B Layer A
(GPa) Layer in B (GPa) E1 A/B/A 18.3 0 5.57 4.53 E2 A/B/A 13.3 0
5.46 4.53
[0107] Interfacial strength of both E1 and E2 was the same or
nearly the same as the strength of the parent material as measured
by a interlaminar fracture toughness test in Mode I (G.sub.lc). Our
attempt to measure the weakest G.sub.lc of the consolidated
tri-layer structure using the double-cantilever beam test was
unsuccessful due to the strength of the interfaces. We were unable
to create the initial crack region between the consolidated
interfaces. Instead, the locus of failure was in the epoxy layer
used to join the consolidated structure to the aluminum beams.
Thus, we know the G.sub.lc of the consolidated interfaces is higher
than that of the epoxy-aluminum interface. Previous studies Alfano
et al., "Analysis of Fracture in Aluminum Joints Bonded with a
Bi-Component Epoxy Adhesive," Journal of Testing and Evaluation,
Vol. 39, No. 2, 2010) reports G.sub.lc values of around 2000
J/m.sup.2 for a similar Aluminum/Epoxy interface. This suggests
that the interfaces of the consolidated interfaces of the tested
sample was higher than 2000 J/m.sup.2.
* * * * *