U.S. patent application number 11/296138 was filed with the patent office on 2006-07-27 for multilayer composite films and articles prepared therefrom.
Invention is credited to Diego Boeri, Geraldine M. Lenges.
Application Number | 20060165929 11/296138 |
Document ID | / |
Family ID | 36091331 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060165929 |
Kind Code |
A1 |
Lenges; Geraldine M. ; et
al. |
July 27, 2006 |
Multilayer composite films and articles prepared therefrom
Abstract
The present invention is an optically transparent laminate film
comprising: at least three layers of film, wherein at least two of
the at least three layers comprise ionomeric films, and wherein the
film can be suitable for use in a photovoltaic cell or in
packaging.
Inventors: |
Lenges; Geraldine M.;
(Wilmington, DE) ; Boeri; Diego; (Geneva,
CH) |
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: |
36091331 |
Appl. No.: |
11/296138 |
Filed: |
December 7, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60634421 |
Dec 7, 2004 |
|
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Current U.S.
Class: |
428/35.7 |
Current CPC
Class: |
B32B 2333/04 20130101;
B32B 2439/00 20130101; B32B 2439/60 20130101; B32B 2605/006
20130101; B32B 27/32 20130101; B32B 2307/734 20130101; B32B 2333/00
20130101; B32B 2553/00 20130101; B32B 2457/12 20130101; H01L
31/0481 20130101; Y02E 10/50 20130101; Y10T 428/31645 20150401;
Y10T 428/1352 20150115; Y10T 428/3158 20150401; B32B 2307/412
20130101; Y10T 428/31928 20150401; Y10T 428/31786 20150401; B32B
27/08 20130101; B32B 27/30 20130101; B32B 2250/03 20130101; B32B
2250/40 20130101; H01L 31/048 20130101; B32B 27/28 20130101; B32B
17/10743 20130101; B32B 2250/24 20130101; B32B 17/10431 20130101;
Y10T 428/31551 20150401; B32B 27/308 20130101; B32B 2323/04
20130101 |
Class at
Publication: |
428/035.7 |
International
Class: |
B32B 27/08 20060101
B32B027/08 |
Claims
1. A laminate article comprising: (i) a first outer layer
comprising a first ionomer; (ii) a core layer unit comprising at
least one polymer layer positioned such that a first surface of the
core layer unit is in direct contact with at least one surface of
the first outer layer; (iii) a second outer layer comprising a
second ionomer positioned such that a second surface of the core
layer unit is in direct contact with at least one surface of the
second outer layer; wherein the at least one core layer polymer is
a non-ionomeric polymer and wherein the individual optical
transmittance for each of the first ionomer layer, the second
ionomer layer, the core layer unit, and the laminate at the same
wavelength can each be measured, and wherein the measured
transmittance for the laminate is greater than the expectation
value of the transmittance calculated from the transmittance of the
three individual layers in their non laminated state weighted by
their thicknesses in the laminate.
2. The laminate article of claim 1 wherein the first and second
ionomers comprise identical compositions.
3. The laminate article of claim 1 wherein the optical
transmittance of the laminate material of light of 500 nm
wavelength is greater than 85%.
4. The laminate article of claim 1 which shows a DMA transition
temperature of greater than 65.degree. C. at 1 Hz.
5. The laminate article of claim 5 wherein the core layer polymer
shows a DMA transition temperature of less than 40.degree. C. at 1
Hz when not laminated to the outer layers.
6. The laminate article of claim 1 wherein the core layer polymer
is a laminate.
7. The laminate article of claim 1 wherein the core layer polymer
comprises a polymer selected from the group consisting of:
polyurethane; ethylene vinyl acetate (EVA); polyvinyl chloride
(PVC); polyester; polyacetals; ethylene acid copolymers (which can
be inclusive of ethylene acid terpolymers or higher copolymers),
ethylene acrylate copolymers (which can be inclusive of terpolymers
and higher copolymers) and blends, laminates or combinations
thereof.
8. The laminate article of claim 1 wherein the first and second
ionomers independently comprise copolymers obtained by the
copolymerization of ethylene and an ethylenically unsaturated
C.sub.3-C.sub.8 carboxylic acid.
9. The laminate article of claim 1 wherein the first and second
ionomers independently comprise an acid copolymer that includes
from about 8 wt % to about 25 wt % of the acid, based on the total
weight of the copolymer.
10. The laminate article of claim 9 wherein the first and second
ionomers independently comprise an acid copolymer that includes
from about 11 wt % to about 25 wt % of the acid, based on the total
weight of the copolymer.
11. The laminate article of claim 10 wherein the first and second
ionomers independently comprise an acid copolymer that includes
from about 14 wt % to about 19 wt % of the acid, based on the total
weight of the copolymer.
12. The laminate article of claim 11 wherein the first and second
ionomers independently comprise an acid copolymer that includes
from about 15 wt % to about 19 wt % of the acid, based on the total
weight of the copolymer.
13. An optically transparent laminate film comprising: at least
three layers of film, wherein (a) at least two of the at least
three layers comprise ionomeric films, (b) at least one layer of
the laminate independently in a non laminated state (i) transmits
less than about 85% incident visible light and/or (ii) has a haze
value of equal to or greater than about 6% as measured according to
ASTM D1003-00 on the at least one layer having a thickness of about
40 mil or less and (c) the transparent laminate (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.
14. An article comprising the optically transparent laminate film
of claim 13.
15. The article of claim 14 wherein the article is a package or
container.
16. The article of claim 15 wherein the article comprises one or
more layers of glass laminated to at least one of the ionomeric
films.
17. A solar cell module comprising: (a) at least one solar cell and
(b) a transparent encapsulant material disposed adjacent to at
least one surface of the solar cell, the encapsulant material
comprises a laminate of claim 1, wherein the solar cell module
further comprises a front support layer formed of light
transmitting material disposed adjacent a front surface of the
encapsulant material and a backskin layer disposed adjacent a rear
surface of the encapsulant material.
18. The solar cell module of claim 17 comprising a plurality of
interconnected solar cells.
19. A laminate article comprising: (i) a first outer layer that
comprises a first ionomer; (ii) a core layer unit comprised of at
least one core layer polymer located with a first surface next to a
surface of the first outer layer; (iii) a second outer layer that
comprises a second ionomer located next to a second surface of the
core layer unit, wherein the core layer polymer is not an ionomer
and the laminate material, the first and second ionomers and the
core layer polymer can be characterized by their transition
temperature measured under tensile conditions at 1 Hz by DMA such
that the value of the transition temperature for the laminate
material is greater than the value of the transition temperature of
the core layer polymer measured under identical conditions and not
in the laminate.
20. The laminate article of claim 19 wherein the first and second
ionomers are the same.
21. The laminate article of claim 20 having a DMA transition
temperature of greater than 65.degree. C. at 100 Hz.
22. The laminate article of claim 21 wherein the core layer polymer
has a DMA transition temperature of less than 40.degree. C. at 100
Hz when not laminated to the outer layers.
23. The laminate article of claim 22 wherein the core layer polymer
is a laminate.
24. The laminate article of claim 23 wherein the core layer polymer
comprises a polymer selected from the group consisting of
polyurethane; ethylene vinyl acetate (EVA); polyvinyl chloride
(PVC); polyester; polyacetals; ethylene acid copolymers (which can
be inclusive of ethylene acid terpolymers or higher copolymers);
ethylene acrylate copolymers (which can be inclusive of terpolymers
and higher copolymers), and blends or combinations thereof.
25. The laminate article of claim 24 wherein the first and second
ionomers independently comprise copolymers obtained by the
copolymerization of ethylene and an ethylenically unsaturated
C.sub.3-C.sub.8 carboxylic acid.
26. The laminate article of claim 25 wherein the first and second
ionomers are independently comprise an acid copolymer that includes
from about 8 wt % to about 25 wt % of the acid, based on the total
weight of the copolymer.
27. The laminate article of claim 26 wherein the first and second
ionomers are independently comprise an acid copolymer that includes
from about 11 wt % to about 25 wt % of the acid, based on the total
weight of the copolymer.
28. The laminate article of claim 27 wherein the first and second
ionomers are independently comprise an acid copolymer that includes
from about 14 wt % to about 19 wt % of the acid, based on the total
weight of the copolymer.
29. The laminate article of claim 28 wherein the first and second
ionomers independently comprise an acid copolymer that includes
from about 15 wt % to about 19 wt % of the acid, based on the total
weight of the copolymer.
Description
[0001] This application claims the priority from U.S. Application
No. 60/634,421, filed Dec. 7, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to laminate films useful in packaging
in general and as encapsulants in photovoltaic modules in
particular. The invention particularly relates to transparent
packaging films comprising ethylene acid copolymer ionomers.
[0004] 2. Description of the Related Art
[0005] Good optical properties are important in packaging materials
in general and solar cell modules in particular because good
performance requires that light incident to the cell be transmitted
efficiently and effectively to the voltage-generating layer. Poor
light transmission reduces the efficiency and/or productivity of
the photovoltaic generation process.
[0006] For example, a common form of solar cell module is made by
interconnecting individually formed and separate solar cells made
for example of crystalline silicon, and then mechanically
supporting and protecting the cells against environmental
degradation by integrating the cells into a laminated solar cell
module. The laminated modules usually comprise a stiff transparent
protective front panel or sheet, and a rear panel or sheet
typically called a "backskin". Disposed between the front and back
sheets so as to form a sandwich arrangement are the interconnected
solar cells and an encapsulant.
[0007] A necessary requirement of the encapsulant (or at least that
portion thereof that extends between the front sides of the cells
and the transparent front panel) is that it be transparent to solar
radiation. The typical mode of forming the laminated module is to
assemble a sandwich comprising in order: a transparent panel, e.g.,
a front panel made of glass or a transparent polymer, a front layer
of at least one sheet of encapsulant, an array of solar cells
interconnected by electrical conductors (with the front sides of
the cells facing the transparent panel), a back layer of at least
one sheet of encapsulant, and a backskin or back panel, and then
bonding those components together under heat and pressure using a
vacuum-type laminator. The back layer of encapsulant may be
transparent or any other color, and prior art modules have been
formed using a backskin consisting of a thermoplastic or
thermosetting polymer, glass or some other material.
[0008] A further requirement of the encapsulant is dimensional
stability. In order to avoid potentially damaging stresses on the
silicon cell, the encapsulant and surrounding structure should be
stable to the temperature fluctuations that are found in end-use
locations of the module.
[0009] A large number of materials have been used or considered for
use as the encapsulant in modules made up of individual silicon
solar cells. Ethylene vinyl acetate copolymer (commonly known as
"EVA") is commonly used as an encapsulant for modules comprising
crystalline silicon solar cells. However, EVA may have certain
limitations or deficiencies, such as its tendency to discolor.
Also, it can decompose and release acetic acid. EVA also can
require cross-linking--for example as described in U.S. Pat. No.
6,093,757--to impart dimensional stability. Cross-linking is a
potential source of variability in the product, and can promote
subsequent oxidation and degradation of EVA. In addition, EVA must
be laminated in a vacuum when making a module because of the
presence of peroxide as a cross-linking promoter in the EVA. EVA
used as an encapsulant material usually contains 33% (by weight) of
vinyl acetate, and thus is a very soft and tacky material that
makes handling EVA in a manufacturing environment somewhat
troublesome.
[0010] The use of ionomer as an encapsulant is described in U.S.
Pat. No. 5,478,402, hereby incorporated herein in its entirety by
reference. The use of ionomer as an encapsulant is further
disclosed in U.S. Pat. No. 5,741,370. The term "ionomer" and the
type of resins identified thereby are well known in the art, as
evidenced by Richard W. Rees, "Ionic Bonding In Thermoplastic
Resins", DuPont Innovation, 1971, 2(2), pp. 1-4, and Richard W.
Rees, "Physical Properties And Structural Features Of Surlyn.RTM.
Ionomer Resins", Polyelectrolytes, 1976, C, 177-197. Ionomers may
be formed by partial neutralization of ethylene-methacrylic acid
copolymers or ethylene-acrylic acid copolymers with organic bases
having cations of elements from Groups I, II, or III of the
Periodic Table, notably, sodium, zinc, aluminum, lithium, magnesium
and barium. Surlyn.RTM. ionomers have been identified as copolymers
of ethylene and methacrylic or acrylic acid that typically have a
melting point in the range of 83-95.degree. C.
[0011] It can be desirable to provide materials that are useful as
encapsulant materials in photovoltaic cells, wherein cross-linking
is not required for acceptable dimensional stability of the
encapsulant material.
SUMMARY OF THE INVENTION
[0012] The present inventors have made the surprising discovery
that one or more physical properties of a polymer can be
significantly improved when the polymer is sandwiched as a core
layer in a laminate between ionomer layers.
[0013] In one aspect, the present invention is a laminate
comprising: at least three polymeric layers which include [0014]
(1) two outer polymeric layers that are ionomeric polymers, and
[0015] (2) at least one core layer unit; wherein each of the outer
layers is in direct contact with opposing surfaces of at least one
surface of a core layer unit, and wherein the at least one core
layer unit is a single or multiple layer polymeric film or sheet
that comprises at least one non-ionomeric polymer layer and wherein
the optical clarity, as measured by the transmittance, and the
dimensional stability of the laminate are each respectively
enhanced over the expected values of said properties for the
individual laminate layers.
[0016] In another aspect, the present invention is a laminate
comprising: [0017] (i) a first outer layer comprising a first
ionomer; [0018] (ii) a core layer unit comprising at least one
polymer layer positioned such that a first surface of the core
layer unit is in direct contact with at least one surface of the
first outer layer; [0019] (iii) a second outer layer comprising a
second ionomer positioned such that a second surface of the core
layer unit is in direct contact with at least one surface of the
second outer layer; wherein the at least one core layer polymer is
a non-ionomeric polymer and wherein the individual optical
transmittance for each of the first ionomer layer, the second
ionomer layer, the core layer unit, and the laminate at the same
wavelength can each be measured, and wherein the measured
transmittance for the laminate is greater than the expectation
value of the transmittance calculated from the transmittance of the
three individual layers in their non laminated state weighted by
their thicknesses in the laminate.
[0020] In another aspect, the present invention is a solar cell
module comprising an encapsulant comprising: [0021] (i) a first
outer layer comprising a first ionomer; [0022] (ii) a core layer
unit comprising at least one polymer layer positioned such that a
first surface of the core layer unit is in direct contact with at
least one surface of the first outer layer; [0023] (iii) a second
outer layer comprising a second ionomer positioned such that a
second surface of the core layer unit is in direct contact with at
least one surface of the second outer layer; wherein the at least
one core layer polymer is a non-ionomeric polymer and wherein the
individual optical transmittance for each of the first ionomer
layer, the second ionomer layer, the core layer unit, and the
laminate at the same wavelength can each be measured, and wherein
the measured transmittance for the laminate is greater than the
expectation value of the transmittance calculated from the
transmittance of the three individual layers in their non laminated
state weighted by their thicknesses in the laminate.
[0024] In another aspect, the present invention is a plurality of
interconnected solar cells comprising an encapsulant comprising;
[0025] (i) a first outer layer comprising a first ionomer; [0026]
(ii) a core layer unit comprising at least one polymer layer
positioned such that a first surface of the core layer unit is in
direct contact with at least one surface of the first outer layer;
[0027] (iii) a second outer layer comprising a second ionomer
positioned such that a second surface of the core layer unit is in
direct contact with at least one surface of the second outer
layer;
[0028] wherein the at least one core layer polymer is a
non-ionomeric polymer and wherein the individual optical
transmittance for each of the first ionomer layer, the second
ionomer layer, the core layer unit, and the laminate at the same
wavelength can each be measured, and wherein the measured
transmittance for the laminate is greater than the expectation
value of the transmittance calculated from the transmittance of the
three individual layers in their non laminated state weighted by
their thicknesses in the laminate.
DETAILED DESCRIPTION OF THE INVENTION
[0029] In one embodiment, the present invention is a laminate
article having (a) outer layers that comprise ionomeric polymers
and (b) a core layer unit that is disposed between the outer layers
and comprises a non ionomeric polymer. In a laminate of the present
invention the measured optical and/or dimensional stability of the
laminate can be enhanced over the expected value of either or both
said properties for the individual layers of the laminate.
[0030] By "expectation value" of a property it is meant the
predicted value of said laminate property as calculated from the
individual layers of the laminate, taking into account the layer
thickness weighted average. By way of illustration, a three layer
laminate wherein each layer has an optical extinction coefficient
would be expected to have an absorbance that is the layer thickness
weighted sum of the individual extinction coefficients. Similarly a
three layer laminate where each layer has a tensile modulus would
be expected to have a tensile modulus that is a layer thickness
weighted average of the individual layers.
[0031] A laminate, as the term is used herein, comprises multiple
polymer layers in face to face relationship among each other,
wherein the adhesion between the layers is such that the layers
remain adhered together during the application of such stresses as
the structure is subjected to during normal or intended use of said
laminate. Adhesion can be accomplished by the use of polymers in
the different layers that adhere to each other during the
manufacture of the material, or by the use of additional adhesives
or primers.
[0032] The outer layers of the present invention are structural
layers of a laminate of the present invention that are positioned
so that they are in direct contact with a core layer unit on at
least one surface of said core layer unit. The outer layers of a
laminate of the present invention contribute to good optical
properties in a laminate of the present invention. The outer layers
of a laminate of the present invention comprise ionomeric polymers
(ionomers). The outer layers each can comprise the identical
ionomer composition to one another or can be different ionomer
compositions from one another. 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 25 wt
% of the acid, based on the total weight of the copolymer. Ionomers
useful as optical layers in the practice of the present invention
preferably comprise from about 11 wt % to about 25 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.
[0033] Ionomers suitable for use herein can include a third
comonomer component which is an ester of an ethylenically
unsaturated C.sub.3-C.sub.8 carboxylic acid. The alkyl substituent
of the ester can preferably be derived from a C.sub.1 to C.sub.12
alcohol, but any unsaturated ester that can provide the optical
properties described herein can be suitable for use in the practice
of the present invention. Conventional ionomers that include a
third comonomer are commercially available from E. I. du Pont de
Nemours and Company, 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.
[0034] A core layer unit of the present invention is a structural
component within a laminate of the present invention that is in
direct contact with at least one outer layer on at least one
surface of the at least one outer layer. The core layer unit of the
present invention provides properties to the laminate that are not
provided by the outer layers alone. For example, the core layer can
provide higher or lower modulus, barrier properties, strength,
absorbancy, permeability, or other properties desirable in a
package or other article.
[0035] The core layer unit can itself be a single polymeric layer,
or a laminated polymeric structure, or multiple plied layers of
film and/or sheet. Any layer included or used in a core layer unit
of the present invention is, for the purposes herein, considered a
core layer. A core layer suitable for use herein can comprise any
polymer that imparts desirable properties to the laminate. For
example, the core layer can be polyurethane, ethylene vinyl acetate
(EVA), polyvinyl chloride (PVC), polyester, polyacetals, ethylene
acid copolymers (which can be inclusive of ethylene acid
terpolymers or higher copolymers), ethylene acrylate copolymers
(which can be inclusive of terpolymers and higher copolymers), or
other polymeric layers that have suitable physical properties and
can be laminated to an ionomer to yield a multilayer film either
directly or through a tie or adhesive layer. A laminate of the
present invention can comprise more than one core layer unit.
[0036] In another embodiment, the present invention is an optically
transparent multilayer laminate film structure comprising at least
three film layers. By optically transparent it is meant that
optical measurements taken on the combination of the at least three
layers of the multilayer film structure are 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 the practice of the present invention, the haze
of the multilayer laminate structure is not greater than 6%.
[0037] A optically transparent laminate of the present invention is
constructed such that the outer layers contact the core layer and
form an interface with opposing surfaces of the at least one core
layer.
[0038] While the laminate structure of the present invention
transmits at least about 85% of the incident light, and/or has a
haze of less than about 6%, the individual components of the
laminate are not required to have optical properties that meet
those standards. In particular, the at least one core layer of the
present invention is not required to have optical properties which
meet the minimum optical standards of the laminate. In fact, it is
one object of the present invention to overcome relatively poor
optical properties in a core layer component by combining core
structural layer(s) with outer layers, or optical layers, of the
present invention described herein, thereby providing a laminate
having acceptable optical properties.
[0039] In another embodiment, an optically transparent multilayer
laminate of the present invention comprises: (1) at least two
ionomeric outer layers having independently transparency of at
least about 85% and/or a haze value of less than about 6%, and (2)
at least one core layer that provides other desirable properties
not provided by the optical layers but having a transparency of
less than about 85% and/or a haze of greater than about 6% when
taken alone and not in a laminate with the outer layers.
[0040] The outer layers can each independently transmit at least
about 85% of incident light. Preferably the outer layers transmit
at least about 88% of incident light, and more preferably at least
about 89% of the incident light. Most preferably the outer layers
transmit at least about 90% of incident light. In a much preferred
embodiment the outer layers can each independently transmit at
least about 91%, 92%, 93%, 94%, 95% or more of incident light. The
haze of the outer layers is preferably less than about 5%, more
preferably less than about 4%, and most preferably less than about
3%. In a particularly preferred embodiment of the present
invention, the haze of the outer layers is less than about 2%, and
can be as low as 1% or less, and light transmission can be at least
98% or even 99% or more.
[0041] In the practice of the present invention the outer layers of
the multilayer film are chemically distinct from the at least one
core layer and can be chemically distinct from each other. To
illustrate by way of example, the percentage of the acid component
in the ionomer can vary between the at least two of the ionomer
layers, as can the level of neutralization of the acid components,
as can the identity of the counterion present in the at least two
ionomers, as can the presence or absence of a third comonomer. Each
of these conditions, and others, can be varied independently or in
combination to make the outer layers chemically distinct from the
core layer and/or from each other. It can be preferable, for
reasons of cost or to reduce complexity, that the outer layers are
identical to each other.
[0042] In a preferred embodiment of the present invention a
laminate of the present invention has a transition temperature as
measured by DMA (and described hereunder in the examples) of
65.degree. C. or more at 1 Hz. More preferably, the transition
temperature of the material is greater than about 65.degree. C. and
that of the core layer alone is 40.degree. C. or less at 1 Hz.
[0043] A transparent multilayer film of the present invention can
be suitable for use as an interlayer in a laminate glazing system
such as: a vehicle windshield or sidelite; as safety glass in
buildings; cabinet glass; glazing in doors; shelving; laminated
glazing in other conventional applications.
[0044] A multilayer film of the present invention surprisingly
exhibits superior optical properties compared to the core layer
alone, and the outer layers provide other physical properties to
the multilayer film. This result is surprising because the optical
layers can provide desirable optical properties in spite of poor
optical properties of the core layer(s).
[0045] The multilayer laminate of the present invention has a total
thickness 40.0 mil or less. Preferably, the laminate can have a
total thickness of 20.0 or less. More preferably, the laminate can
have a total thickness of 10.0 mil or less, and even more
preferably a thickness of 4.0 mil or less. Even more preferably,
the laminate can have a total thickness of about 3.0 mil or less,
or 2.0 mil or less. The thickness required of a multilayer film can
be a balance between obtaining structural properties required to
protect the contents of a package, for example, and achieving other
goals such as meeting optical requirements of transparency, using
cost-effective materials, and/or minimizing production costs.
[0046] The outer layers of the present invention can be thinner
than the core layers of the present invention, but this may not be
a requirement in all applications of the present invention. The
thickness of the outer layer(s) can each independently be about 50%
or less of the thickness of the outer layer. The outer layers of a
laminate of the present invention can each independently have a
thickness of 20.0 mil or less, preferably 15 mil or less, and more
preferably 10 mil or less, with the proviso that any film thickness
can be varied to balance the desirable optical and other physical
properties, with the practical aspects of producing a
cost-effective film.
[0047] A multilayer laminate film of the present invention can be
useful in a variety of applications and can be suitable for use in
combination with glass, or clear plastic, to make optically clear
or transparent laminate articles such as solar cell modules, or
laminated windows, or other safety glass, or plastic bottles, or
squeezable bottles.
[0048] In another embodiment, the present invention is a
photovoltaic cell in which a light sensitive silicon device is
disposed against one of the ionomer comprising layers of the
multilayer laminate ("the first layer") wherein the outer layers
comprise ionomers and an inner, core, layer comprises a non
ionomeric polymer. The light sensitive portion of the silicon
device faces the three layer laminate. The other surface of the
silicon device is disposed against a second layer that may comprise
a second three layer laminate, or any polymer that can form a seal
against the first layer. The second layer may also comprise a
backsheet layer, and the backsheet layer can be laminated with the
second layer or separate therefrom.
[0049] In a preferred embodiment the invention is a solar cell
module comprising at least one solar cell which in turn comprises a
transparent encapsulant material positioned adjacent to at least
one surface of the solar cell. The encapsulant material comprises a
laminate material further comprising: [0050] (i) a first outer
layer comprising a first ionomer; [0051] (ii) a core layer unit
comprising at least one polymer layer positioned such that a first
surface of the core layer unit is in direct contact with at least
one surface of the first outer layer; [0052] (iii) a second outer
layer comprising a second ionomer positioned such that a second
surface of the core layer unit is in direct contact with at least
one surface of the second outer layer; wherein the at least one
core layer polymer is a non-ionomeric polymer and wherein the
individual optical transmittance for each of the first ionomer
layer, the second ionomer layer, the core layer unit, and the
laminate at the same wavelength can each be measured, and wherein
the measured transmittance for the laminate is greater than the
expectation value of the transmittance calculated from the
transmittance of the three individual layers in their non laminated
state weighted by their thicknesses in the laminate.
[0053] A module of the present invention further comprises a front
support layer formed of light transmitting material disposed
adjacent a front surface of the encapsulant material and a backskin
layer disposed adjacent a rear surface of the encapsulant
material.
[0054] The solar cell module can further comprise at least one
solar cell that in turn comprises a plurality of interconnected
solar cells.
[0055] In another embodiment, the present invention is a laminate
that comprises outer layers that in turn comprise ionomers, and a
core layer that is disposed between the outer layers and comprises
a non ionomeric polymer such that the phase transition temperature
of the laminate is enhanced over what would be expected from the
individual laminate layers alone. It is possible for the laminated
structure to have a DMA phase transition temperature under dynamic
mechanical analysis that is higher than the phase transition
temperature of the material from which the core material is
fabricated. The enhanced transition temperature yields a material
which is dimensionally stable at ambient temperatures. Optionally
the laminates of this embodiment have optical transparency, however
this embodiment of the invention is not limited to transparent
laminates.
EXAMPLES
[0056] 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.
[0057] In the following experiments cast film was made on a Sano
multi-layer extrusion line. The total structure of thickness 460
microns structure comprised of 25 micron thick identical
Surlyn.RTM. 1705-1 (Du Pont, Wilmington, Del.) outer layers
bounding a 410 micron thick core layer comprising a second
resin.
[0058] Secant Modulus was measured on film samples (Instru-Met load
frame 1122 tensile tester using ASTM D 882-01)
[0059] % Haze was measured on film samples (BYK Gardner haze-gard
plus using ASTM D 1003-00)
[0060] % Transmittance was measured on film samples (Varian Cary 5
uv/vis/nir, System I.D. Cary5-1081139 scanned from 800 nm to 200 nm
and reported at 500 nm). The expectation value of the transmittance
was calculated as the layer thickness weighted value calculated
from the absorbance per unit thickness of the materials that each
layer comprised.
[0061] Dynamic mechanical analysis (DMA) was conducted in order to
ascertain the dimensional stability of the samples. The experiments
were run on a Seiko DMS 210 in tensile mode from ambient to
150.degree. C. at 1.degree. C./min heating rate, 1 Hz frequency and
10 .mu.m amplitude. By "DMA transition" is meant the temperature at
which the gradient of the length of the specimen vs temperature
plot sharply changes direction, indicating either shrinkage or
expansion of the sample, that is a lack of dimensional stability
(dimensional instability), at the given temperature.
[0062] In the following examples, Elvaloy.RTM. 1330 is
ethylene-methyl acrylate copolymer with 30% MA and 3 melt index
(MI). Elvaloy.RTM. 1335 is ethylene-methyl acrylate copolymer with
35% MA and 3 MI. Elvaloy.RTM. 3427 is ethylene-butyl acrylate
copolymer with 27% BA and 4 MI. Surlyn.RTM. 1705-1 is a 5.5 MI,
zinc-neutralized ethylene-methacrylic acid copolymer and
Surlyn.RTM. 1857 is a 4 MI, zinc-neutralized ethylene-methacrylic
acid-isobutyl acrylate terpolymer. TABLE-US-00001 DMA Data Control
Samples Observed DMA Film Composition Transition (.degree. C.)
S1705 82 S1857 NM E1335 33 E1330 35 E3427 38 Laminate Samples Film
Composition Observed Transition S1705/E1330/S1705 78
S1705/E1335/S1705 75 S1705/E3427/S1705 74 NM = Not Measured.
[0063] DMA data at 1 Hz from 0 .degree.C.- 150 .degree.C. indicate
that having a thin laminate of Surlyn.RTM. (1-mil) outside an EMA
core (16-mil) proveds dimensional stability of the multi-layer
structure at from ambient temperatures up to more than 70
.degree.C. with results almost equivalent to the mono-layer
Surlyn.RTM. 1705-1. TABLE-US-00002 Optical and Tensile Data Control
samples Observed Observed MD Transmittance Secant Modulus TD
Modulus Film Composition (%) (psi) (psi) S1705 90.5 29459 26930
S1857 89.4 NM NM E1335 37.3 992 744 E1330 34.1 1727 1458 E3427 75.7
3310 3310 Laminate samples Expectation Observed Film Composition
Transmittance (%) Transmittance (%) S1705/S1875/S1705 89.4 89.7
S1705/E1330/S1705 38.0 88.1 S1705/E1335/S1705 41.2 85.1
S1705/E3427/S1705 77.2 88.1 Tensile Data (Secant Modulus) Expected
Observed Expected Observed MD MD TD TD modulus Modulus modulus
Modulus Film Composition (psi) (psi) (psi) (psi) S1705/E1330/S1705
4808 4733 4288 5071 S1705/E1335/S1705 4155 4320 3654 4846
S1705/E3427/S1705 6215 7498 5934 7729
[0064] The transparency of tri-layer structures is improved over
monolayer Elvaloy.RTM. AC films, however the advantages of the low
modulus of the EMA is retained, while the dimensional stability as
measured by the DMA transition) of tri-layer structure is also
significantly improved over monolayer Elvaloy.RTM. AC films. The
need for cross linking of the core layer is obviated.
[0065] The present invention has been described with regard to
certain embodiments and examples. However one skilled in the art
will be able with obvious modifications to modify the invention.
The scope of the invention as claimed is intended to include all
such modifications and is not to be construed to be limited to the
examples and embodiments described herein.
* * * * *