U.S. patent application number 11/165159 was filed with the patent office on 2006-04-20 for transparent ionomeric films from blends of ionomeric copolymers.
Invention is credited to Richard J. Arhart, Geraldine M. Lenges.
Application Number | 20060084763 11/165159 |
Document ID | / |
Family ID | 34979093 |
Filed Date | 2006-04-20 |
United States Patent
Application |
20060084763 |
Kind Code |
A1 |
Arhart; Richard J. ; et
al. |
April 20, 2006 |
Transparent ionomeric films from blends of ionomeric copolymers
Abstract
The present invention is a film obtained from a blend of
chemically distinguishable copolymers, wherein the film has a light
transmission of at least 85%, and/or a haze of less than 6%, and
wherein the blend comprises a component copolymer has a secant
modulus of less than 15,000 when cast independently into a
film.
Inventors: |
Arhart; Richard J.;
(Wilmington, DE) ; Lenges; Geraldine M.;
(Wilmington, DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
34979093 |
Appl. No.: |
11/165159 |
Filed: |
June 23, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60582563 |
Jun 24, 2004 |
|
|
|
Current U.S.
Class: |
525/195 |
Current CPC
Class: |
C08L 23/0876 20130101;
C08J 5/18 20130101; C08L 23/0869 20130101; B32B 17/10743 20130101;
C08L 23/0876 20130101; C08L 2666/06 20130101; C08L 23/0869
20130101; C08L 2666/06 20130101; C08J 2323/08 20130101; C08L
2205/02 20130101; B32B 27/32 20130101 |
Class at
Publication: |
525/195 |
International
Class: |
C08F 8/00 20060101
C08F008/00 |
Claims
1. A blend of at least a first copolymer and a second copolymer
each of said copolymers being chemically distinguishable and being
obtained by copolymerization of ethylene each independently with at
least one other comonomer, wherein the at least one other comonomer
is independently an ethylenically unsaturated carboxylic acid or
derivative thereof, and wherein a film obtained from the blend (a)
has a secant modulus of less than about 15,000 psi as measured
according to ASTM D882-01 and (b) (i) transmits at least about 85%
of incident visible light and/or (ii) has a haze value of equal to
or less than about 6% as measured according to ASTM D1003-00.
2. The blend of claim 1 wherein the at least first and second
copolymers are ionomers.
3. A film obtained from the blend of claim 1.
4. The film of claim 3 having a modulus as measured according to
ASTM D882-01 which is less than that which would be predicted from
a composition weighted average of the moduli of films obtained by
producing films individually from the first copolymer and the
second copolymer and further optional copolymers alone.
5. The film of claim 3 that transmits at least about 88% of
incident visible light or (ii) has a haze value of equal to or less
than about 3% as measured according to ASTM D1003-00.
6. The film of claim 5 wherein the at least first and second
copolymers are ionomers.
7. The film of claim 6 wherein the at least first and second
ionomers are derived from copolymers that each independently
comprises from about 8 wt % to about 20 wt % of carboxylic acid
monomer, based on the total weight of the copolymer.
8. The film of claim 7 wherein the at least first and second
ionomers are derived from copolymers that each independently
comprises from about 12 wt % to about 20 wt % of carboxylic acid
monomer, based on the total weight of the copolymer.
9. The film of claim 8 wherein the at least first and second
ionomers are derived from copolymers that each independently
comprises from about 14 wt % to about 19 wt % of carboxylic acid
monomer, based on the total weight of the copolymer.
10. The film of claim 9 wherein the first copolymer is present in a
range of from about 20 wt % to about 60 wt %, and the second
copolymer is present in a range of from about 80 wt % to about 40
wt %, and wherein the first copolymer is an ionomer component
having a secant modulus of less than about 15,000 and the second
copolymer is an ionomer component having an optical transmission of
at least about 87%.
11. A composition obtained from the melt extrusion of a blend of a
first copolymer, a second copolymer and optional further copolymers
each of said copolymers being chemically distinguishable and being
obtained by copolymerization of ethylene with at least one other
comonomer, wherein the at least one other comonomer is an
ethylenically unsaturated carboxylic acid or derivative thereof,
and wherein a film obtained from the blend (a) has a secant modulus
of less than about 15,000 psi as measured according to ASTM D882-01
and (b) (i) transmits at least about 85% of incident visible light
or (ii) has a haze value of equal to or less than about 6% as
measured according to ASTM D1003-00.
12. A film obtained from the blend of claim 11.
13. A photovoltaic cell module that comprises at least one
encapsulant layer comprising an optically transparent film, said
film comprising a blend of a first copolymer, a second copolymer
and optional further copolymers each of said copolymers being
chemically distinguishable and being obtained by copolymerization
of ethylene each with at least one other comonomer, wherein the at
least one other comonomer is independently an ethylenically
unsaturated carboxylic acid or derivative thereof, and wherein the
film (a) has a secant modulus of less than about 15,000 psi as
measured according to ASTM D882-01 and (b) (i) transmits at least
about 85% of incident visible light or (ii) has a haze value of
equal to or less than about 6% as measured according to ASTM
D1003-00.
14. A process for preparing an optically transparent film having a
modulus of less than about 15,000 psi as measured according to ASTM
D882-01 wherein the film (i) transmits at least about 85% of
incident visible light or (ii) has a haze value of equal to or less
than about 6% as measured according to ASTM D1003-00, the process
comprising the step of: blending at least two chemically
distinguishable copolymers that are each obtained by
copolymerization of ethylene with at least one other comonomer,
wherein the at least one other comonomer is an ethylenically
unsaturated carboxylic acid.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/582,563, filed Jun. 24, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to films useful as encapsulants for
photovoltaic (solar) cells. This invention particularly relates to
films comprising ethylene acid copolymer ionomers useful as
encapsulants for photovoltaic cells.
[0004] 2. Description of the Related Art
[0005] In applications where good optical properties are important,
it can be a requirement to have a film that is substantially
transparent to light. Films useful in applications where optical
properties are important may not have other physical or mechanical
properties--such as, for example modulus--suitable for use in the
desired field of use.
[0006] Blends of ionomers have found particular application in golf
ball covers. For example U.S. Pat. No. 5,587,430 to DuPont
describes an ionomer composition for improved high temperature
performance.
[0007] U.S. Pat. No. 5,567,772 to DuPont describes an ionomer blend
comprising a polymer that is an ethylene/acid copolymer ionomer
which is a partially neutralized copolymer of ethylene and
methacrylic acid or acrylic acid.
[0008] Golf ball covers have been obtained from blends of high acid
ionomers with other ionomers. For example U.S. Pat. No. 5,873,796
to Acushnet Company claims a golf ball comprising a core and at
least one cover layer comprising a blend of a high acid ionomer
formed from an acid copolymer having an acid content of 19 weight
percent; and an ionomer formed from an acid copolymer having an
acid content of 15 weight percent.
[0009] Blends of high and low modulus ionomers for use in a golf
ball have been described in U.S. Pat. No. 5,415,937.
[0010] U.S. Pat. No. 4,884,814 to Spalding teaches blending a hard
ionomer resin with a soft ionomer resin to produce a golf ball
cover.
[0011] U.S. Pat. No. 5,120,791 to Lisco describes a composition for
use in a golf ball said to have enhanced carrying distance.
[0012] Other patents of interest that demonstrate the current state
of the art in blending of ionomers are U.S. Pat. Nos. 5,688,869,
5,691,418, and 5,328,959.
[0013] The teaching of the golf ball related art describes blended
compositions suitable for use in a golf ball cover or other parts
of a golf ball. It is of note, however, that transparency and haze
(optical properties) are not properties that are considered
critical or of any influence to golf ball performance or
acceptance.
[0014] Blending ionomers having a modulus that is acceptable for an
encapsulant application with other ionomers having acceptable
optical properties can result in optical properties and modulus
that are intermediate between the properties of the components.
This can be an unsatisfactory result where improved optical
properties or modulus are desirable.
[0015] It would therefore be desirable to provide an ionomer film
that incorporates both the physical and optical properties
desirable for use in applications where both physical properties
and optical properties of a film are important.
SUMMARY OF THE INVENTION
[0016] The present inventors have made the surprising discovery
that it is possible to blend ionomers and obtain a film product
that is more flexible than would be expected based on the moduli of
the component polymers and yet without a sacrifice in the optical
clarity that would be expected from blending two chemically
distinguishable materials. Indeed, the optical clarity is very
close to that of the more clear component in the mixture.
[0017] In one embodiment, the present invention is a blend of at
least two chemically distinguishable copolymers that are each
obtained by copolymerization of ethylene with at least one other
comonomer, wherein the at least one other comonomer is an
ethylenically unsaturated carboxylic acid, and wherein a film
obtained from the blend (a) has a secant modulus of less than about
15,000 psi as measured according to ASTM D882-01 and (b) (i)
transmits at least about 85% of incident visible light and/or (ii)
has a haze value of equal to or less than about 6% as measured
according to ASTM D1003-00.
[0018] In another aspect, the present invention is the product that
is obtained after melt extrusion of a blend of at least two
chemically distinguishable copolymers that are each obtained by
copolymerization of ethylene with at least one other comonomer,
wherein the at least one other comonomer is an ethylenically
unsaturated carboxylic acid, and wherein a film obtained from the
blend (a) has a secant modulus of less than about 15,000 psi as
measured according to ASTM D882-01 and (b) (i) transmits at least
about 85% of incident visible light and/or (ii) has a haze value of
equal to or less than about 6% as measured according to ASTM
D1003-00.
[0019] In a still another aspect, the present invention is a film
obtained by extruding, casting, or blowing a blend of at least two
chemically distinguishable copolymers that are each obtained by
copolymerization of ethylene with at least one other comonomer,
wherein the at least one other comonomer is an ethylenically
unsaturated carboxylic acid, and wherein a film obtained from the
blend (a) has a secant modulus of less than about 15,000 psi as
measured according to ASTM D882-01 and (b) (i) transmits at least
about 85% of incident visible light and/or (ii) has a haze value of
equal to or less than about 6% as measured according to ASTM
D1003-00.
[0020] In still another aspect, the present invention is a film
which has a modulus which is less than would be predicted from a
composition weighted average of the moduli of films obtained by
casting or blowing from the first copolymer and the second
copolymer and further optional copolymers alone.
[0021] In another aspect, the present invention is a process for
preparing an optically transparent film having a modulus of less
than about 15,000 psi as measured according to ASTM D882-01 wherein
the film (i) transmits at least about 85% of incident visible light
and/or (ii) has a haze value of equal to or less than about 6% as
measured according to ASTM D1003-00, the process comprising the
step of: blending at least two chemically distinguishable
copolymers that are each obtained by copolymerization of ethylene
with at least one other comonomer, wherein the at least one other
comonomer is an ethylenically unsaturated carboxylic acid.
[0022] In a still further aspect the invention is a photovoltaic
(solar) cell module that comprises at least one encapsulant layer
comprising an optically transparent film, said film comprising a
blend of a first copolymer, a second copolymer and optional further
copolymers each of said copolymers being chemically distinguishable
and being obtained by copolymerization of ethylene each with at
least one other comonomer, wherein the at least one other comonomer
is independently an ethylenically unsaturated carboxylic acid or
derivative thereof, and wherein the film (a) has a secant modulus
of less than about 15,000 psi as measured according to ASTM D882-01
and (b) (i) transmits at least about 85% of incident visible light
and/or (ii) has a haze value of equal to or less than about 6% as
measured according to ASTM D1003-00.
DETAILED DESCRIPTION OF THE INVENTION
[0023] By "chemically distinguishable" as applied to two polymeric
materials it is meant that the two materials have different monomer
compositions in the polymer chain. For example, two ionomers that
are copolymers of ethylene and a second acid comonomer are
chemically distinguishable for the purposes of the present
invention if they have different mole percentages (and/or different
weight percentages) of the two comonomers in the chain or,
alternatively, they are considered chemically distinct if at least
one of the comonomers in one of the copolymers has a distinct
chemical identity from either of the comonomers in the other
material.
[0024] In one embodiment the present invention is an optically
transparent film, wherein the film can be obtained from a blend of
suitable polymer resins. By optically transparent it is meant that
the film of the present invention is at least 85% transparent to
light in the visible region of the light spectrum. Optical
transparency can be related to the haze of the multilayer laminate
film. In one embodiment of the present invention, the haze of the
film is not greater than 6%.
[0025] In a further embodiment, the present invention is a blend of
a first copolymer, a second copolymer and optional further
copolymers each of said copolymers being chemically distinguishable
and being obtained by copolymerization of ethylene with at least
one other comonomer, wherein the at least one other comonomer is an
ethylenically unsaturated carboxylic acid, and wherein a film
obtained from the blend (a) has a secant modulus of less than about
15,000 psi as measured according to ASTM D882-01 and (b) (i)
transmits at least about 85% of incident visible light and/or (ii)
has a haze value of equal to or less than about 6% as measured
according to ASTM D1003-00.
[0026] In the practice of the present invention, the blend or the
optically transparent film comprises at least two chemically
distinguishable copolymer resins of ethylene and an ethylenically
unsaturated carboxylic acid, or a derivative, or an equivalent
thereof. For example, ethylene copolymers with acrylic acid and/or
methacrylic acid (referred to hereinafter in any combination as
(meth)acrylic acid) can be preferred. Derivatives or equivalents of
carboxylic acids are well-known to one of ordinary skill in the art
and can be used alternatively to, or in addition to, the carboxylic
acid comonomer. Such acid derivatives or equivalents, for example,
are: esters; anhydrides; acid salts; acid halides; amides;
nitrites, and the like. Salts of ethylene/(meth)acrylic acid
copolymers (either fully or partially neutralized) are
conventionally known as ionomers, and are particularly preferred in
the practice of the present invention.
[0027] The polymers can be selected based on the optical and
physical properties of a film obtained from the individual
components. For example, a suitable blend candidate can have a
secant modulus of less than about 35,000 psi, preferably less than
about 30,000, and more preferably less than about 25,000. Most
preferably, the secant modulus of a film obtained from a component
of the blend is less than about 20,000. In a much preferred
embodiment, the components of the blend are selected such that at
least one component, when in combination with the other
component(s), will provide the final film with a secant modulus of
less than about 15,000.
[0028] A component of the blend can also be selected on the basis
of its optical properties as measured on a film obtained therefrom.
For example, a film obtained from a component of the blend
preferably has a percent transmission (% T) of greater than about
85%, more preferably greater than about 87%, even more preferably
greater than about 88%, and most preferably greater than about 90%.
In a particularly preferred embodiment, the components of the blend
are selected such that a film obtained from the blend has a secant
modulus of less than about 15,000 and optical transmission of at
least about 85%. Preferably a film obtained from a blend of the
present invention has a secant modulus of less than about 14,000,
and more preferably less than about 13,000. Most preferably, the
secant modulus of the film is less than about 12,000 and the
optical transmission is greater than about 88%.
[0029] A film can be obtained from the blend of the invention by
any means known to one skilled in the art, and which may include,
without limitation, melt extrusion followed by casting the melt
onto a cold surface or using a gas to blow a bubble from the melt
that is then cooled and solidified. The means for obtaining a film
can also include a process such as dissolution solvent evaporation
or precipitation.
[0030] The haze of a film of the present invention is preferably
less than about 5%, more preferably less than about 4%, and most
preferably less than about 3%. It is surprising that a blend can
provide a film having optical properties that are on the same order
as a monocomponent film. It is generally accepted by those of
ordinary skill in the art that ionomers that differ by more than 3
wt % acid are not readily miscible, and can result in haze levels
that are undesirable in a film that is intended to have low
haze.
[0031] The components can be blended in any proportion suitable and
appropriate to provide a film that has optical and physical
properties that are suitable for use as an encapsulant layer in a
solar cell.
[0032] A blend of the present invention can be prepared by
conventional blending processes such as, for example, dry-blending
of pellets, melt-blending, or co-extrusion.
[0033] Ionomers useful in the practice of the present invention are
copolymers obtained by the copolymerization of ethylene and an
ethylenically unsaturated C.sub.3-C.sub.8 carboxylic acid.
Preferably the unsaturated carboxylic acid is either acrylic acid
or methacrylic acid. The acid copolymer preferably includes from
about 8 wt % to about 20 wt % of the acid, based on the total
weight of the copolymer. Ionomers useful herein preferably comprise
from about 12 wt % to about 20 wt % acid, more preferably from
about 14 wt % to about 19 wt % acid, and most preferably from about
15 wt % to about 19 wt % acid. Less than about 12 wt % acid can
result in too low transmittance or too high haze of the optical
layers. It is to be understood that in the present invention the
acid component described is inclusive of any neutralized acid that
exists in the salt form. If the acid is methacrylic acid, the acid
copolymer preferably includes from about 15 wt % to about 25 wt %
methacrylic acid. In the final blends, the acid groups in the
copolymer are highly neutralized to include from about 65 mole % to
about 100 mole % of the neutralized acid carboxylate. Conventional
ionomers of this type can be obtained commercially from E.I. du
Pont de Nemours and Company (DuPont), for example.
[0034] In a particularly preferred embodiment of the present
invention, two ionomeric components can be combined in a proportion
ranging from about 20 wt % Component 1:80 wt % Component 2 to about
60 wt % Component 1:40 wt % Component 2, wherein Component 1 is an
ionomer component having a secant modulus of less than about 15,000
and Component 2 is an ionomer component having an optical
transmission of at least about 87%.
[0035] Conventional ionomers can include, in addition to the
ethylene and acid components, a third comonomer component which is
an ester of an ethylenically unsaturated carboxylic acid.
Conventional ionomers that include a third comonomer are
commercially available from DuPont, for example, and can be
suitable for use in the practice of the present invention so long
as the optical and physical properties are suitable for application
in the present invention.
[0036] A film of the present invention can be useful in a variety
of applications. The film of the present invention can exhibit
excellent adhesion to glass as well as to other materials such as,
for example, plastic and/or other transparent materials, and thus
can be suitable for use in combination with glass, or clear
plastic, to make optically clear or transparent laminate articles,
laminated windows or safety glass.
EXAMPLES
[0037] The Examples and Comparative Examples are presented for
illustrative purposes only, and are not intended to limit the scope
of the present invention in any manner.
[0038] In the following Examples and Comparative Examples the
resins used are as follows:
Resin 1--ionomeric resin, 15 wt % methacrylic acid 1.2% zinc ion,
Ml of 5.5;
Resin 2--acid copolymer resin, 11.5 wt % acrylic acid, Ml of 1.5;
Resin 3--ionomeric resin, 10 wt % methacrylic acid 0.75% zinc ion,
Ml of 4.0.
[0039] The expected values (EV) of the modulus was the linear
combination that is established by calculating the weight (for EV
1) or mole (for EV 2) average modulus from the moduli of the
individual components.
Comparative Example 1
[0040] Resin 1 was extruded in a Werner Pfleiderer 30 mm twin-screw
extruder. The barrel temperatures were set at 150.degree. C.
(rear), 160.degree. C. (center rear), 190.degree. C. (center),
190.degree. C. (front), 190.degree. C. (adaptor), and 190.degree.
C. (die). The resin was extruded at approximately 80 amps, 230 RPM,
440 psi and 210.degree. C. melt temperature. A cast film was
prepared from the extrudate on a 1.1 D cast film line. The haze of
the film was determined according to ASTM D1003-00. The
transmittance (% T) was determined using a Varian Cary 5 uv/vis/nir
system. The film was scanned from 800 nm to 200 nm, and % T
reported at 500 nm. The secant modulus was determined according to
ASTM D882-01. The results are given in Table 1.
Comparative Example 2
[0041] The procedure of Comparative Example 1 was repeated except
that the film was obtained from 100 wt % Resin 2.
Comparative Example 3
[0042] The procedure of Comparative Example 1 was repeated except
that the film was obtained from 100 wt % Resin 3.
Example 1
[0043] The procedure of Comparative Example 1 was repeated except
that the 2 mil monolayer film was obtained from a blend of 25 wt %
Resin 1 with 75 wt % Resin 3. Haze, secant modulus, and % T are
reported in Table 1.
Example 2
[0044] The procedure of Example 1 was repeated except that resins 1
and 3 were combined in a ration of 50:50. Haze, secant modulus, and
% T are reported in Table 1.
Example 3
[0045] The procedure of Example 1 was repeated except that resins 1
and 2 were combined in a ration of 50:50. Haze, secant modulus, and
% T are reported in Table 1. TABLE-US-00001 TABLE 1 Modulus (2 %
Transmittance Example trials) Haze (%) EV 1 EV 2 C1 29,302/32,183
2.26 90.6 C2 19,935/19,728 2.67 88.4 C3 9,957/10,212 2.23 88.1 1
11,757/11,549 2.24 89.4 15,249 14,922 2 15,529/14,359 2.18 88.7
20,414 19,969 3 22,845/22,659 3.53 90.1 25,287 24,968
[0046] It is evident from the table that the actual modulus values
that were obtained from the blends were at or below the values
expected on the basis of either weight or mole fraction of
components in the blend. However the transmittance numbers were
improved over those of the low modulus component. In particular
with blend examples 1 and 2, the transmittance that was obtained
was close to that of the stiffer component, while the modulus was
close to that of the softer component.
[0047] All aforementioned patents and patent applications are
herein incorporated by reference in their entirety.
[0048] While it is apparent that the invention herein disclosed is
well calculated to fulfill the objects above stated, it will be
appreciated that numerous modifications and embodiments may be
devised by those skilled in the art. It is intended that the
appended claims cover all such modifications and embodiments as
fall within the true spirit and scope of the present invention.
* * * * *