U.S. patent application number 14/698965 was filed with the patent office on 2015-10-29 for solar cell modules with improved backsheet.
The applicant listed for this patent is E I DU PONT DE NEMOURS AND COMPMANY. Invention is credited to RICHARD T CHOU, TIMOTHY A. LIBERT, BARRY ALAN MORRIS, BENJAMIN ANDREW SMILLIE, JINGJING XU.
Application Number | 20150311370 14/698965 |
Document ID | / |
Family ID | 53200297 |
Filed Date | 2015-10-29 |
United States Patent
Application |
20150311370 |
Kind Code |
A1 |
CHOU; RICHARD T ; et
al. |
October 29, 2015 |
SOLAR CELL MODULES WITH IMPROVED BACKSHEET
Abstract
Disclosed is a polyamide-ionomer composition suitable for use in
a backsheet in a photovoltaic module comprising a polymer component
a polyamide and an anhydride ionomer comprising a copolymer of
ethylene, an alpha, beta-unsaturated C.sub.3-C.sub.8 carboxylic
acid and an ethylenically unsaturated dicarboxylic acid or
derivative thereof selected from the group consisting of maleic
acid, fumaric acid, itaconic acid, maleic anhydride, and a
C.sub.1-C.sub.1 alkyl half ester of maleic acid, wherein the
carboxylic acid functionalities present are at least partially
neutralized to carboxylate salts of one or more alkali metal,
transition metal, or alkaline earth metal cations; 0 to 20 weight %
of pigment; and 0 to 40 weight % of filler; preferably wherein the
combination of pigment and filler comprises 10 to 50 weight % of
the composition; and 0 to 5 weight % of weatherability
additives.
Inventors: |
CHOU; RICHARD T; (Hockessin,
DE) ; LIBERT; TIMOTHY A.; (HOCKESSIN, DE) ;
MORRIS; BARRY ALAN; (WILMINGTON, DE) ; SMILLIE;
BENJAMIN ANDREW; (KINGSTON, CA) ; XU; JINGJING;
(WILINGTON, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
E I DU PONT DE NEMOURS AND COMPMANY |
Wilmington |
DE |
US |
|
|
Family ID: |
53200297 |
Appl. No.: |
14/698965 |
Filed: |
April 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61985579 |
Apr 29, 2014 |
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Current U.S.
Class: |
136/251 ; 438/66;
524/514 |
Current CPC
Class: |
B32B 2270/00 20130101;
C08L 77/06 20130101; C08K 2003/2241 20130101; B32B 2264/105
20130101; B32B 2307/4026 20130101; C08L 23/0876 20130101; B32B
2264/102 20130101; H01L 31/049 20141201; B32B 2307/412 20130101;
C08L 77/02 20130101; C08L 2203/204 20130101; B32B 2307/736
20130101; B32B 2457/12 20130101; B32B 2307/726 20130101; C08K 3/22
20130101; C08K 3/34 20130101; C08L 77/06 20130101; B32B 27/08
20130101; B32B 27/20 20130101; C08L 77/02 20130101; C08L 77/06
20130101; B32B 2307/54 20130101; Y02E 10/50 20130101; C08K 3/2279
20130101; B32B 27/34 20130101; B32B 2264/104 20130101; C08L
2203/206 20130101; C08K 3/34 20130101; C08K 3/2279 20130101; C08K
3/2279 20130101; C08K 3/34 20130101; C08L 23/0876 20130101; C08K
3/22 20130101; C08K 3/34 20130101; C08L 23/0876 20130101; C08K 3/34
20130101; C08L 23/0876 20130101; C08K 3/22 20130101; C08L 23/0876
20130101; B32B 2307/418 20130101; C08L 23/08 20130101; C08L 77/02
20130101 |
International
Class: |
H01L 31/048 20060101
H01L031/048; H01L 31/18 20060101 H01L031/18; C08L 77/02 20060101
C08L077/02; H01L 31/049 20060101 H01L031/049; C08L 23/08 20060101
C08L023/08 |
Claims
1. A polyamide-ionomer blend composition comprising (i) A polymer
component comprising 1) 53 to 64 weight %, based on the combination
of (1) and (2), of a polyamide component; 2) 36 to 47 weight %,
based on the combination of (1) and (2), of an anhydride ionomer
component comprising a copolymer of (a) ethylene; (b) from 5 weight
% to 15 weight % of an alpha, beta-unsaturated C3-C.sub.8
carboxylic acid; (c) from 0.5 weight % to 12 weight % of at least
one comonomer that is an ethylenically unsaturated dicarboxylic
acid or derivative thereof selected from maleic acid, fumaric acid,
itaconic acid, maleic anhydride, or a C.sub.1-C.sub.4 alkyl half
ester of maleic acid; and (d) from 0 weight % to 30 weight % of
monomers selected from alkyl acrylate or alkyl methacrylate,
wherein the alkyl groups have from one to twelve carbon atoms;
wherein the carboxylic acid functionalities present are at least
partially neutralized to carboxylate salts comprising one or more
alkali metal, transition metal, or alkaline earth metal cations;
(ii) 0 to 20 weight % of pigment; and (iii) 0 to 40 weight % of
filler; and (iv) 0 to 5 weight % of weathering additives selected
from oxidation inhibitors, UV stabilizers and hindered amine light
stabilizers.
2. The composition of claim 1 wherein the combination of (ii) and
(iii) comprises 8 to 50 weight % of the combination of (i), (ii),
(iii) and (iv).
3. The composition of claim 1 wherein the polyamide component
comprises nylon 6, nylon 12, nylon 610, nylon 612, nylon 610/6T,
nylon 612/6T, or combinations thereof.
4. The composition of claim 1 wherein the polyamide component
comprises nylon 6.
5. The composition of claim 1 wherein the comonomer of (c) is a
C.sub.1-C.sub.4 alkyl half ester of maleic acid.
6. The composition of claim 1 wherein the carboxylic acid
functionalities present are at least partially neutralized to
carboxylate salts comprising zinc or sodium.
7. The composition of claim 5 wherein the carboxylic acid
functionalities present are at least partially neutralized to
carboxylate salts comprising zinc.
8. The composition of claim 1 comprising 8 to 20 weight % of
pigment and 0 weight % filler.
9. The composition claim 1 comprising 8 to 40 weight % of filler
and 0 weight % of pigment.
10. The composition of claim 1 comprising 10 to 40 weight % of
filler and 8 to 15 weight % of pigment.
11. The composition of claim 1 comprising 8 to 12 weight % of
pigment and 12 to 18 weight % of filler.
12. The composition of claim 1 wherein the pigment comprises
titanium dioxide, zinc oxide, or antimony oxide.
13. The composition of claim 1 wherein the filler comprises an
inorganic oxide, carbonate, sulfate, silica, alkali and alkaline
earth metal silicate, or baryte of a metal of Groups IA, IIA, IIIA,
IIB, VIB or VIII of the periodic table of the elements.
14. The composition of claim 13 wherein the filler comprises
calcium carbonate, barium sulfate, wollastonite or talc.
15. The composition of claim 14 wherein the filler comprises
talc.
16. The composition of claim 1 comprising 10 to 40 weight % of talc
and 8 to 15 weight % of titanium dioxide.
17. A backsheet for a photovoltaic module comprising the
composition of claim 1.
18. The backsheet of claim 17 wherein the polyamide component
comprises nylon 6.
19. The backsheet of claim 17 wherein the pigment comprises
titanium dioxide, zinc oxide, or antimony oxide.
20. The backsheet of claim 17 wherein the filler comprises calcium
carbonate, barium sulfate, wollastonite or talc.
21. The backsheet of claim 20 wherein the filler comprises
talc.
22. The backsheet of claim 17 wherein the polyamide-ionomer blend
composition comprises 10 to 40 weight % of talc and 8 to 15 weight
% of titanium dioxide.
23. A laminated solar cell module comprising a front support layer
formed of a light transmitting material and having first and second
surfaces; a plurality of interconnected solar cells having a first
surface facing the front support layer and a second surface facing
away from the front support layer; a transparent encapsulant
surrounding and encapsulating the interconnected solar cells, the
transparent encapsulant being bonded to the second surface of the
front support layer; and a backsheet of claim 17 wherein one
surface of the backsheet is bonded to the second surface of the
transparent encapsulant.
24. An assembly for conversion under heat and pressure into a
laminated solar cell module, the assembly comprising a front
support layer formed of a light transmitting material and having
front and back surfaces; a first transparent thermoplastic
encapsulant layer adjacent to the back surface of the front support
layer; a plurality of interconnected solar cells having first and
second surfaces adjacent to the first transparent encapsulant
layer; a second transparent thermoplastic encapsulant layer
disposed adjacent to the solar cells in parallel relation to the
first transparent encapsulant layer; and a thermoplastic backsheet
of claim 17.
25. A method of manufacturing a solar cell module comprising
providing a front support layer formed of a light transmitting
material and having front and back surfaces; placing a first
transparent thermoplastic encapsulant layer adjacent to the back
surface of the front support layer; positioning a plurality of
interconnected solar cells having first and second surfaces so that
the first surfaces thereof are adjacent to the first transparent
encapsulant layer; placing a second transparent thermoplastic
encapsulant layer adjacent to the second surfaces of the solar
cells; placing a backsheet of claim 17 adjacent to the second
transparent thermoplastic encapsulant layer to thereby form an
assembly; subjecting the assembly to heat and pressure so as to
melt the encapsulant layers and cause the encapsulant to surround
the solar cells, and cooling the assembly so as to cause the
encapsulant to solidify and bond to the front support layer, the
solar cells and the backsheet, thereby laminating the layers and
the solar cells together to form an integrated solar cell module.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C.
.sctn.119(e) from U.S. Provisional Patent Application No.
61/985,579, filed Apr. 29, 2014, hereby incorporated herein by
reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to photovoltaic solar cell modules
having an improved backsheet.
BACKGROUND OF THE INVENTION
[0003] A common form of solar cell module or photovoltaic (PV)
module is made by interconnecting individually formed and separate
solar cells, e.g., crystalline silicon solar cell, 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 "backsheet" or "backskin". Interconnected
solar cells and an encapsulant are disposed between the front and
back sheets so as to form a sandwich arrangement. 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, a sheet of scrim to facilitate gas
removal during the lamination process, and a backsheet 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 backsheet consisting of a
thermoplastic polymer, glass or some other material.
[0004] Although the lamination process seals the several layered
components together throughout the full expanse of the module, it
is common practice to apply a protective polymeric edge sealant to
the module so as to assure that moisture will not penetrate the
edge portion of the module. The polymeric edge sealant may be in
the form of a strip of tape or a caulking-type compound. Another
common practice is to provide the module with a perimeter frame,
usually made of a metal like aluminum, to provide mechanical edge
protection. Those techniques are disclosed or suggested in U.S.
Pat. No. 5,741,370. That patent also discloses the concept of
eliminating the back layer of encapsulant and bonding a
thermoplastic backskin directly to the interconnected solar
cells.
[0005] A large number of materials have been used or considered for
use as the encapsulant in modules made up of individual silicon
solar cells. Until at least around 1995, ethylene vinyl acetate
copolymer (commonly known as "EVA") was considered the best
encapsulant for modules comprising crystalline silicon solar cells.
However, EVA has certain limitations: (1) it decomposes under
sunlight, with the result that it discolors and gets progressively
darker, and (2) its decomposition releases acetic acid which in
turn promotes further degradation, particularly in the presence of
oxygen and/or heat.
[0006] U.S. Pat. No. 5,478,402 discloses use of an ionomer as a
cell encapsulant substitute for EVA. The use of ionomer as an
encapsulant is further disclosed in U.S. Pat. No. 5,741,370.
Ionomers are acid copolymers in which a portion of the carboxylic
acid groups in the copolymer are neutralized to salts containing
metal ions. U.S. Pat. No. 3,264,272 discloses a composition
comprising a random copolymer of copolymerized units of an
alpha-olefin having from two to ten carbon atoms, an alpha,
beta-ethylenically-unsaturated carboxylic acid having from three to
eight carbon atoms in which 10 to 90 percent of the acid groups are
neutralized to salts with metal ions from Groups I, II, or III of
the Periodic Table, notably, sodium, zinc, lithium, or magnesium,
and an optional third mono-ethylenically unsaturated comonomer such
as methyl methacrylate or butyl acrylate.
[0007] It is known to use a rear panel or backsheet that is made of
the same material as the front panel, but a preferred and common
practice is to make it of a different material, preferably a
material that weighs substantially less than glass, such as a
polyvinyl fluoride polymer available under the tradename
Tedlar.RTM. from E.I. Du Pont de Nemours Co. (DuPont). A widely
used backsheet material is a Tedlar.RTM./polyester/ethylene vinyl
acetate laminate. Another common backsheet uses a trilayer
structure of Tedlar.RTM./Polyester/Tedlar.RTM., also called
TPT.TM., described in WO 94/22172. This structure allows the
fluoropolymer to protect both sides of the polyester from
photo-degradation. However, Tedlar.RTM. and Tedlar.RTM. laminates
are not totally impervious to moisture, and as a consequence over
time the power output and/or the useful life of modules made with
this kind of backsheet material is reduced due to electrical
shorting resulting from absorbed moisture.
[0008] Due to the price and the supply concern, the PV industry has
been gradually evaluating new alternatives, such as backsheets
derived from PET, polyamides, etc. For example, WO 2008/138021
discloses PV modules with backsheets based on polyamides derived
from linear and/or branched aliphatic and/or cycloaliphatic
monomers, which have an average of at least 8 and most 17 carbon
atoms, such as nylon 12. However, polyamides are semi-crystalline
polymers with high degree of crystallinity, which can lead to
brittleness, low flexibility and excessive shrinkage. High moisture
absorption is especially a problem for nylon-6 and nylon-66, the
most inexpensive polyamides. Water absorption causes dimensional
instability, poor weatherability, and, most importantly, reduces
insulation capability. While nylon-11 and nylon-12 have better
moisture resistance and weatherability, the melting temperature may
be too low for use in some lamination processes of PV module
assembly.
[0009] U.S. Pat. No. 5,741,370 discloses using as the backskin
material a thermoplastic olefin comprising a combination of two
different ionomers, e.g., a sodium ionomer and a zinc second
ionomer, with that combination being described as producing a
synergistic effect which improves the water vapor barrier property
of the backskin material over and above the barrier property of
either of the individual ionomer components. The patent also
discloses use of an ionomer encapsulant with the dual ionomer
backskin.
[0010] It is known that thermoplastic blends or alloys based on
ionomers and polyamides have a combination of desirable properties
(see U.S. Pat. Nos. 4,174,358, 5,688,868, 5,866,658, 6,399,684,
6,569,947, 6,756,443 and 7,144,938, 7,592,056, 8,057,910, 8,062,757
and 8,119,235). For example, U.S. Pat. No. 5,866,658 discloses a
blend of an ionomer dispersed in a continuous or co-continuous
polyamide phase in the range of 60/40 weight % to 40/60 weight %
used for molded parts exhibiting toughness, high gloss,
abrasion/scratch resistance, and high temperature properties. U.S.
Pat. No. 6,399,684 discloses similar blends also containing
phosphorous salts such as a hypophosphite salt. See also U.S.
Patent Applications 2002/0055006, 2005/007462, 2006/0142489,
2008/0161503, 2009/0298372, 2013/0167966, 2013/0171390,
2013/0171394, 2013/0172470 and 2013/0172488.
[0011] U.S. Pat. Nos. 5,700,890, 5,859,137, 7,267,884 and U.S.
Patent Application Publications 2005/0020762A1, and 2006/0142489A1
disclose polyamides toughened with ionomers of ethylene copolymers
containing a monocarboxylic acid and a dicarboxylic acid or
derivative thereof. U.S. Patent Application Publication
2011/0020573 discloses a blend comprising a polyamide, an ionomer
of an ethylene copolymer containing a monocarboxylic acid and a
dicarboxylic acid or derivative thereof, and a sulfonamide. U.S.
Pat. No. 8,586,663 discloses a blend comprising a polyamide, an
ionomer of an ethylene copolymer containing a monocarboxylic acid
and a dicarboxylic acid or derivative thereof, and a second
ionomer. U.S. Pat. No. 7,592,056 discloses blends of polyamides
with mixed ion ionomers, including zinc and sodium mixtures.
[0012] U.S. Pat. No. 6,660,930 discloses photovoltaic modules
comprising backskins comprising a nylon/ionomer alloy.
[0013] Photovoltaic modules can be assessed for moisture permeation
and weatherability by cyclic treatment with high moisture and
temperature and cold temperature in standardized "stress tests". It
is desirable to provide PV modules that are capable of withstanding
such stress tests for substantially more than 1000 hours. Thus, it
also is desirable to provide backsheet materials that provide PV
modules that are capable of withstanding such stress tests.
SUMMARY OF THE INVENTION
[0014] This invention relates to a polyamide-ionomer composition
suitable for use in a backsheet in a photovoltaic module.
[0015] The polyamide-ionomer blend composition comprises, or
consists essentially of [0016] (i) A polymer component comprising,
or consisting essentially of [0017] 1) 53 to 64 weight %, based on
the combination of (1) and (2), of a polyamide; [0018] 2) 36 to 47
weight %, based on the combination of (1) and (2), of an anhydride
ionomer comprising, or consisting essentially of a copolymer of
[0019] (a) ethylene; [0020] (b) from 5 weight % to 15 weight % of
an alpha, beta-unsaturated C.sub.3-C.sub.8 carboxylic acid; [0021]
(c) from 0.5 weight % to 12 weight % of at least one comonomer that
is an ethylenically unsaturated dicarboxylic acid or derivative
thereof selected from the group consisting of maleic acid, fumaric
acid, itaconic acid, maleic anhydride, and a C.sub.1-C.sub.4 alkyl
half ester of maleic acid; and [0022] (d) from 0 weight % to 30
weight % of monomers selected from alkyl acrylate and alkyl
methacrylate, wherein the alkyl groups have from one to twelve
carbon atoms; wherein the carboxylic acid functionalities present
are at least partially neutralized by one or more alkali metal,
transition metal, or alkaline earth metal cations; [0023] (ii) 0 to
20 weight % of pigment; and [0024] (iii) 0 to 40 weight % of
filler; preferably wherein the combination of (ii) and (iii)
comprises 8 to 50 weight % of the combination of (i), (ii), (iii)
and (iv); and [0025] (iv) 0 to 5 weight % of additives selected
from oxidation inhibitors, UV stabilizers, and hindered amine light
stabilizers.
[0026] The invention provides a backsheet for a photovoltaic module
comprising or consisting essentially of the composition described
above.
[0027] The invention also provides a laminated solar cell module
comprising or consisting essentially of a front support layer
formed of a light transmitting material and having first and second
surfaces; a plurality of interconnected solar cells having a first
surface facing the front support layer and a second surface facing
away from the front support layer; a transparent encapsulant
surrounding and encapsulating the interconnected solar cells, the
transparent encapsulant being bonded to the second surface of the
front support layer; and a backsheet as described above wherein one
surface of the backsheet is bonded to the second surface of the
transparent encapsulant.
[0028] The invention also provides an assembly for conversion under
heat and pressure into a laminated solar cell module, the assembly
comprising a front support layer formed of a light transmitting
material and having front and back surfaces; a first transparent
thermoplastic encapsulant layer adjacent to the back surface of the
front support layer; a plurality of interconnected solar cells
having first and second surfaces adjacent to the first transparent
encapsulant layer; a second transparent thermoplastic encapsulant
layer disposed adjacent to the solar cells in parallel relation to
the first transparent encapsulant layer; and a thermoplastic
backsheet as described above.
[0029] The invention also provides a method of manufacturing a
solar cell module comprising providing a front support layer formed
of a light transmitting material and having front and back
surfaces; placing a first transparent thermoplastic encapsulant
layer adjacent to the back surface of the front support layer;
positioning a plurality of interconnected solar cells having first
and second surfaces so that the first surfaces thereof are adjacent
to the first transparent encapsulant layer; placing a second
transparent thermoplastic encapsulant layer adjacent to the second
surfaces of the solar cells; placing a backsheet as described above
adjacent to the second transparent thermoplastic encapsulant layer
to thereby form an assembly; subjecting the assembly to heat and
pressure so as to melt the encapsulant layers and cause the
encapsulant to surround the solar cells, and cooling the assembly
so as to cause the encapsulant to solidify and bond to the front
support layer, the solar cells and the backsheet, thereby
laminating the layers and the solar cells together to form an
integrated solar cell module.
DETAILED DESCRIPTION OF THE INVENTION
[0030] All publications, patent applications, patents, and other
references mentioned herein are incorporated by reference in their
entirety.
[0031] As used herein, the terms "comprises," "comprising,"
"includes," "including," "has," "having" or any other variation
thereof, are intended to cover a non-exclusive inclusion. For
example, a process, method, article, or apparatus that comprises a
list of elements is not necessarily limited to only those elements
but may include other elements not expressly listed or inherent to
such process, method, article, or apparatus. Further, unless
expressly stated to the contrary, "or" refers to an inclusive or
and not to an exclusive or. For example, a condition A or B is
satisfied by any one of the following: A is true (or present) and B
is false (or not present), A is false (or not present) and B is
true (or present), and both A and B are true (or present). As used
herein, the terms "a" and "an" include the concepts of "at least
one" and "one or more than one".
[0032] Unless stated otherwise, all percentages, parts, ratios,
etc., are by weight. Further, when an amount, concentration, or
other value or parameter is given as either a range, preferred
range or a list of upper preferable values and lower preferable
values, this is to be understood as specifically disclosing all
ranges formed from any pair of any upper range limit or preferred
value and any lower range limit or preferred value, regardless of
whether ranges are separately disclosed. Where a range of numerical
values is recited herein, unless otherwise stated, the range is
intended to include the endpoints thereof, and all integers and
fractions within the range. It is not intended that the scope of
the invention be limited to the specific values recited when
defining a range. When a component is indicated as present in a
range starting from 0, such component is an optional component
(i.e., it may or may not be present). When present an optional
component may be at least 0.1 weight % of the composition or
copolymer.
[0033] When materials, methods, or machinery are described herein
with the term "known to those of skill in the art", "conventional"
or a synonymous word or phrase, the term signifies that materials,
methods, and machinery that are conventional at the time of filing
the present application are encompassed by this description. Also
encompassed are materials, methods, and machinery that are not
presently conventional, but that may have become recognized in the
art as suitable for a similar purpose.
[0034] As used herein, the term "copolymer" refers to polymers
comprising copolymerized units resulting from copolymerization of
two or more comonomers and may be described with reference to its
constituent comonomers or to the amounts of its constituent
comonomers such as, for example "a copolymer comprising ethylene
and 15 weight % of acrylic acid". A description of a copolymer with
reference to its constituent comonomers or to the amounts of its
constituent comonomers means that the copolymer contains
copolymerized units (in the specified amounts when specified) of
the specified comonomers.
[0035] In this application, the terms "sheet", "layer" and "film"
are used in their broad sense interchangeably to describe articles
wherein the compositions are processed into generally planar forms,
either monolayer or multilayer. The processing method and/or the
thickness may influence whether the term "sheet" or "film" is used
herein, but either term can be used to describe such generally
planar articles.
[0036] A "frontsheet" is a sheet, layer or film positioned as the
outermost layer on the side of a photovoltaic module that faces a
light source and may also be described as an incident layer.
Because of its location, it is generally desirable that the
frontsheet has high transparency to the desired incident light to
allow efficient transmission of sunlight into the solar cells. It
is also desirable that the frontsheet has high moisture barrier
properties to prevent entry of moisture into the photovoltaic
module. Such moisture intrusion can degrade the photovoltaic module
components and/or reduce the electrical efficiency of the
module.
[0037] A "backsheet" is a sheet, layer or film on the side of a
photovoltaic module that faces away from a light source, and is
often opaque. In some instances, it may be desirable to receive
light from both sides of a device (e.g. a bifacial device), in
which case a module may have transparent layers on both sides of
the device.
[0038] "Encapsulant" layers are layers used to encase the fragile
voltage-generating solar cell layer to protect it from damage and
hold it in place in the photovoltaic module and are normally
positioned between the solar cell layer and the incident layer and
the backing layer. Suitable polymer materials for these encapsulant
layers typically possess a combination of characteristics such as
high transparency, high impact resistance, high penetration
resistance, high moisture resistance, good ultraviolet (UV) light
resistance, good long term thermal stability, adequate adhesion
strength to frontsheets, backsheets, and other rigid polymeric
sheets and cell surfaces, and good long term weatherability.
[0039] This invention involves the use of a polyamide-ionomer alloy
in sheet form as a backsheet material. As used herein, the term
"alloy" is used to describe a polymer blend that forms a distinct
polymer substance. Various polyamide-ionomer alloys are available.
The composition limits as defined in the Summary of the Invention
above provide that the fraction of polyamide is sufficient to
ensure the polyamide remains the continuous phase during alloying
and subsequent converting to film and the fraction of the ionomer
is sufficient to ensure adequate toughness as made and after aging
as well as good adhesion to the encapsulant.
[0040] Thermoplastic resins are polymeric materials that can flow
when heated under pressure. Melt index (MI) is the mass rate of
flow of a polymer through a specified capillary under controlled
conditions of temperature and pressure. It is typically measured
according to ASTM 1238.
[0041] This invention provides a polymeric blend that is a marriage
of a polyamide such as nylon 6 and an ionomer selected from a
special family of ionomers (denoted anhydride ionomers) to provide
materials that are highly suitable for polymeric backsheets for PV
modules. In essence, the new materials overcome some of the major
deficiencies of both polyamides and ionomers, while continuing to
retain most of the desirable attributes. As indicated above, the
ionomers used in this invention are selected from a family of
ionomers containing dicarboxylic acid moieties, or derivatives
thereof. As used herein, the term "anhydride ionomer" is used to
describe an ionomer that includes dicarboxylic acid moieties,
derivatives thereof such as anhydrides or other known carboxylic
acid derivatives. The presence of dicarboxylic acid moieties in the
ionomers enhances the compatibility with polyamides, particularly
at higher levels, and provides blends with very good toughness, low
temperature impact strength and resistance to hydrolytic
delamination. Higher amounts of dicarboxylic acid moieties provide
two unique features to blends of such ionomers and a polyamide,
such as nylon 6. First, the anhydride ionomer is dispersed in the
polyamide in extremely fine particles and second, the particle size
distribution is very narrow.
[0042] As indicated above, this invention provides a backsheet for
a PV module comprising a thermoplastic composition comprising a
polyamide and an ionomeric composition comprising or consisting
essentially of a copolymer of ethylene, an alpha,beta-unsaturated
C.sub.3-C.sub.8 carboxylic acid, at least one comonomer that is an
ethylenically unsaturated dicarboxylic acid or derivative thereof,
and optionally at least one comonomer selected from alkyl acrylate
and alkyl methacrylate.
[0043] Ionomeric resins ("ionomers") are ionic copolymers of an
olefin such as ethylene (E) with a metal salt of an unsaturated
carboxylic acid, such as acrylic acid (AA), methacrylic acid (MAA),
and/or other acids, and optionally softening comonomers. At least
one alkali metal, transition metal, or alkaline earth metal cation,
such as lithium, sodium, potassium, magnesium, calcium, or zinc, or
a combination of such cations, is used to neutralize some portion
of the acidic groups in the copolymer resulting in a thermoplastic
resin exhibiting enhanced properties. For example, a copolymer of
ethylene and acrylic acid can then be at least partially
neutralized to salts comprising one or more alkali metal,
transition metal, or alkaline earth metal cations to form an
ionomer. Copolymers can also be made from an olefin such as
ethylene, an unsaturated carboxylic acid and other comonomers such
as alkyl (meth)acrylates providing "softer" resins that can be
neutralized to form softer ionomers.
[0044] The ionomers useful in this invention consist of a family of
ionomers containing dicarboxylic acid moieties that can be derived
from ethylenically unsaturated derivatives of dicarboxylic acid
comonomers, such as maleic anhydride and ethyl hydrogen maleate, at
least partially neutralized by one or more alkali metal, transition
metal, or alkaline earth metal cations (denoted as anhydride
ionomers). They are copolymers of ethylene, an
.alpha.,.beta.-unsaturated C.sub.3-C.sub.8 carboxylic acid and at
least one comonomer that is an ethylenically unsaturated
dicarboxylic acid at an amount of from 0.5 weight % to 12 weight %,
alternatively from 3 weight % to 12 weight %. Preferably, the
dicarboxylic acid comonomer(s) are present in an amount from 4
weight % to 10 weight %. The unsaturated dicarboxylic acid
comonomers or their derivatives can be selected from, for example,
maleic anhydride (MAH), ethyl hydrogen maleate (also known as
maleic acid monoethylester--MAME), and itaconic acid (ITA). More
preferably, a copolymer comprises from 4 to 8 weight % of maleic
acid monomethylester comonomer in an ethylene/methacrylic
acid/maleic acid monomethylester copolymer wherein from 20 to 70
percent of the total acid groups in the copolymer are neutralized
to provide carboxylate salts containing alkali metal, transition
metal, or alkaline earth metal cations.
[0045] Some non-neutralized ethylene acid copolymers comprising
lower amounts of ethylenically unsaturated dicarboxylic acid
comonomers are known (see U.S. Pat. No. 5,902,869), as are their
ionomeric derivatives (see U.S. Pat. No. 5,700,890).
[0046] As indicated above, comonomers such as alkyl (meth)acrylates
can be included in the ethylene acid copolymer to form a copolymer
that can be neutralized to provide carboxylate salts with alkali
metal, alkaline earth metal or transition metal cations. Preferred
are comonomers selected from alkyl acrylate and alkyl methacrylate
wherein the alkyl groups have from 1 to 8 carbon atoms, and more
preferred are comonomers selected from methyl acrylate, ethyl
acrylate, iso-butyl acrylate (iBA), and n-butyl acrylate (nBA). The
alkyl (meth)acrylates are optionally included in amounts from 0 to
30 weight % alkyl (meth)acrylate such as 0.1 to 30 weight % when
present and preferably from 0.1 to 15 weight % of the
copolymer.
[0047] Examples of copolymers useful in this invention include
copolymers of ethylene, methacrylic acid and ethyl hydrogen maleate
(E/MAA/MAME) and copolymers of ethylene, acrylic acid and maleic
anhydride (E/AA/MAH).
[0048] Neutralization of the ethylene acid copolymer can be
effected by first making the ethylene acid copolymer and treating
the copolymer with inorganic base(s) with alkali metal, alkaline
earth metal or transition metal cation(s). The copolymer can be
from 10 to 99.5% neutralized with at least one metal ion selected
from lithium, sodium, potassium, magnesium, calcium, barium, lead,
tin, zinc, aluminum; or combinations of such cations.
Neutralization may be from 10 to 70%. Preferably the copolymer has
from 20%, alternatively from 35%, to 70% of the available
carboxylic acid groups ionized by neutralization with at least one
metal ion selected from sodium, zinc, lithium, magnesium, and
calcium; and more preferably zinc or sodium. Notably the carboxylic
acid functionalities present are at least partially neutralized to
carboxylate salts comprising zinc or sodium, preferably zinc. Of
particular note is an anhydride ionomer comprising zinc as the
neutralizing cation.
[0049] Mixed metal ionomers may provide a combination of better
properties to the blends with polyamides than ionomers comprising a
single type of cation. For example, a zinc/sodium mixed ion ionomer
blended with polyamide may provide lower water sorption, better
scratch resistance and better processing capability than those
provided by a corresponding ionomer containing only an alkali metal
such as sodium. The zinc/sodium mixed ion ionomer may also provide
higher hardness and higher mechanical strength than provided by a
corresponding ionomer containing only zinc. Mixed ion ionomers are
conveniently prepared by blending an ionomer composition with a
single cation, such as a zinc-containing ionomer, with an ionomer
with a different cation, such as a sodium-containing ionomer.
Alternatively, mixed ion ionomers may be prepared by neutralizing
an acid copolymer with different neutralizing agents, either
sequentially or simultaneously.
[0050] Methods for preparing ionomers from copolymers are well
known in the art.
[0051] Of note are blends of polyamides and anhydride ionomers
further comprising conventional ionomers prepared from acid
copolymers not containing a dicarboxylic acid or derivative.
Accordingly, compositions of this invention include blends of
polyamide with component (2) further comprising in combination with
the anhydride ionomer one or more conventional ionomer comprising
an E/X/Y copolymer where E is ethylene, X is a C.sub.3 to C.sub.8
.alpha.,.beta.-ethylenically unsaturated monocarboxylic acid, and Y
is a comonomer selected from alkyl acrylate and alkyl methacrylate
wherein the alkyl groups have from 1 to 8 carbon atoms, wherein X
is present in from 2 to 30 weight % of the E/X/Y copolymer, Y is
present from 0 to 40 weight % of the E/X/Y copolymer, wherein the
carboxylic acid functionalities present are at least partially
neutralized by one or more alkali metal, transition metal, or
alkaline earth metal cations. Preferred
.alpha.,.beta.-ethylenically unsaturated monocarboxylic acids
include acrylic acid and methacrylic acid. Non-limiting,
illustrative examples of conventional ionomers include E/15MAA/Na,
E/19MAA/Na, E/15AA/Na, E/19AA/Na, E/15MAA/Mg, E/19MAA/Li, and
E/15MAA/60Zn (wherein E represents ethylene, MAA represents
methacrylic acid, AA represents acrylic acid, the numbers
represents either the weight % of comonomer(s) present in the
copolymer or the amount of neutralization of the available
carboxylic acid groups, and the atomic symbol represents the
neutralizing cation).
[0052] Depending on the need of a particular application, the
amount of such conventional ionomer or mixture of conventional
ionomers in combination with the anhydride ionomer in component (2)
can be manipulated to provide an appropriate balance of toughness,
low temperature impact strength and resistance to hydrolytic
delamination. For example, highly toughened polyamide compositions
can be achieved by using relatively larger amounts of conventional
ionomers with smaller amounts of anhydride ionomers (for example,
30 weight % of conventional ionomer and 6 weight % of anhydride
ionomer). Toughened polyamide films can be prepared using
relatively larger amounts of anhydride ionomers with smaller
amounts of conventional ionomers (for example, 30 weight % of
anhydride ionomer and 6 weight % of conventional ionomer). Of note
are modifier blends comprising equal amounts of anhydride ionomer
and conventional ionomer (for example, 18 weight % of anhydride
ionomer and 18 weight % of conventional ionomer). When a
conventional ionomer is blended with an anhydride ionomer, the
blend desirably contains combined amounts of each of the comonomers
within the ranges described in the Summary of the Invention for the
ionomeric copolymer.
[0053] Notably, when the polyamide is poly(caprolactam) (nylon-6),
the ionomer component consists of an anhydride ionomer.
[0054] The polyamide-ionomer blend may comprise, consist
essentially of consist of or be produced from, a polyamide in an
amount from a lower limit of 53, 58 or 60 weight % to an upper
limit of 64 weight % and an anhydride ionomer in an amount from a
lower limit of 36 or 40 weight % to an upper limit of 42, or 47
weight %, all based on the weight of the combination of polyamide
and anhydride ionomer.
[0055] Polyamides (abbreviated herein as PA), also referred to as
nylons, are condensation products of one or more dicarboxylic acids
and one or more diamines, and/or one or more aminocarboxylic acids
such as 11-aminododecanoic acid, and/or ring-opening polymerization
products of one or more cyclic lactams such as caprolactam and
laurolactam. Polyamides may be fully aliphatic or semiaromatic.
[0056] Polyamides from single reactants such as lactams or amino
acids, referred to as AB type polyamides are disclosed in Nylon
Plastics (edited by Melvin L. Kohan, 1973, John Wiley and Sons,
Inc.) and include nylon-6, nylon-11, nylon-12, or combinations of
two or more thereof. Polyamides prepared from more than one lactam
or amino acid include nylon-6,12.
[0057] Other well-known polyamides useful in the composition
include those prepared from condensation of diamines and diacids,
referred to as AABB type polyamides (including nylon-66, nylon-610,
nylon-612, nylon-1010, and nylon-1212), as well as from a
combination of lactams, diamines and diacids such as nylon-6/66,
nylon-6/610, nylon-6/66/610, nylon-66/610, or combinations of two
or more thereof.
[0058] Fully aliphatic polyamides used in the composition are
formed from aliphatic and alicyclic monomers such as diamines,
dicarboxylic acids, lactams, aminocarboxylic acids, and their
reactive equivalents. In this context, the term "fully aliphatic
polyamide" also refers to copolymers derived from two or more such
monomers and blends of two or more fully aliphatic polyamides.
Linear, branched, and cyclic monomers may be used.
[0059] Carboxylic acid monomers comprised in the fully aliphatic
polyamides include, but are not limited to aliphatic dicarboxylic
acids, such as for example adipic acid (C6), pimelic acid (C7),
suberic acid (C8), azelaic acid (C9), decanedioic acid (C10),
dodecanedioic acid (C12), tridecanedioic acid (C13),
tetradecanedioic acid (C14), and pentadecanedioic acid (C15).
Diamines can be chosen among diamines with four or more carbon
atoms, including but not limited to tetramethylene diamine,
hexamethylene diamine, octamethylene diamine, decamethylene
diamine, dodecamethylene diamine, 2-methylpentamethylene diamine,
2-ethyltetramethylene diamine, 2-methyloctamethylenediamine;
trimethylhexamethylenediamine, meta-xylylene diamine, and/or
mixtures thereof.
[0060] Semi-aromatic polyamides include a homopolymer, a copolymer,
a terpolymer or more advanced polymers formed from monomers
containing aromatic groups. One or more aromatic carboxylic acids
may be terephthalic acid or a mixture of terephthalic acid with one
or more other carboxylic acids, such as isophthalic acid, phthalic
acid, 2-methyl terephthalic acid and naphthalic acid. In addition,
the one or more aromatic carboxylic acids may be mixed with one or
more aliphatic dicarboxylic acids, as disclosed above.
Alternatively, an aromatic diamine such as meta-xylylene diamine
(MXD) can be used to provide a semi-aromatic polyamide, an example
of which is MXD6, a homopolymer comprising MXD and adipic acid.
[0061] Preferred polyamides disclosed herein are homopolymers or
copolymers wherein the term copolymer refers to polyamides that
have two or more amide and/or diamide molecular repeat units. The
homopolymers and copolymers are identified by their respective
repeat units. For copolymers disclosed herein, the repeat units are
listed in decreasing order of mole % repeat units present in the
copolymer. The following list exemplifies the abbreviations used to
identify monomers and repeat units in the homopolymer and copolymer
polyamides:
HMD hexamethylene diamine (or 6 when used in combination with a
diacid) T Terephthalic acid
6-Caprolactam
[0062] AA Adipic acid DDA Decanedioic acid DDDA Dodecanedioic acid
I Isophthalic acid MXD meta-xylylene diamine TMD 1,4-tetramethylene
diamine 6T polymer repeat unit formed from HMD and T MXD6 polymer
repeat unit formed from MXD and AA 66 polymer repeat unit formed
from HMD and AA 610 polymer repeat unit formed from HMD and DDA 612
polymer repeat unit formed from HMD and DDDA 11 polymer repeat unit
formed from 11-aminoundecanoic acid 12 polymer repeat unit formed
from 12-aminododecanoic acid
[0063] In the art the term "6" when used alone designates a polymer
repeat unit formed from .di-elect cons.-caprolactam. Alternatively
"6" when used in combination with a diacid such as T, for instance
6T, the "6" refers to HMD. In repeat units comprising a diamine and
diacid, the diamine is designated first. Furthermore, when "6" is
used in combination with a diamine, for instance 66, the first "6"
refers to the diamine HMD, and the second "6" refers to adipic
acid. Likewise, repeat units derived from other amino acids or
lactams are designated as single numbers designating the number of
carbon atoms.
[0064] In various embodiments the polyamide comprises one or more
polyamides selected from among the following groups (wherein PA is
shorthand for polyamide or "nylon"):
[0065] Group I polyamides have a melting point of less than
210.degree. C., and comprise an aliphatic or semiaromatic polyamide
such as poly(hexamethylene dodecanediamide/hexamethylene
terephthalamide) (PA612/6T). See PCT Patent Application Publication
WO2011/94542. Group I polyamides may have semiaromatic repeat units
to the extent that the melting point is less than 210.degree. C.
and generally the semiaromatic polyamides of the group have less
than 40 mole percent of semiaromatic repeat units. Semiaromatic
repeat units are defined as those derived from monomers selected
from one or more of the group consisting of aromatic dicarboxylic
acids having 8 to 20 carbon atoms and aliphatic diamines having 4
to 20 carbon atoms. Other notable Group I polyamides include
PA6/66, PA6/610, PA6/66/610, PA6/6T, PA1010, PA11 and PA12.
[0066] Group II polyamides have a melting point of at least
210.degree. C. and comprise an aliphatic polyamide. Notable Group
II polyamides include PA6, PA66, PA610 and PA612. The RV of PA6 is
commonly measured according to ISO Test Method 307 using a solution
of 1% of polymer in 96% sulfuric acid. The RV of PA66 is commonly
measured according to ISO Test Method 307 using a solution of 1% of
polymer in 90% formic acid.
[0067] Group III polyamides have a melting point of at least
210.degree. C. and comprise
[0068] (aa) 20 to 35 mole percent semiaromatic repeat units derived
from one or more monomers selected from
[0069] (i) aromatic dicarboxylic acids having 8 to 20 carbon atoms
and aliphatic diamines having 4 to 20 carbon atoms; and
[0070] (bb) 65 to 80 mole percent aliphatic repeat units derived
from one or more monomers selected from
[0071] (ii) an aliphatic dicarboxylic acid having 6 to 20 carbon
atoms and an aliphatic diamine having 4 to 20 carbon atoms; and
[0072] (iii) a lactam and/or aminocarboxylic acid having 4 to 20
carbon atoms.
[0073] A preferred Group III polyamide is PA66/6T.
[0074] Group IV polyamides have a melting point of greater than
230.degree. C. and comprise
[0075] (cc) 50 to 95 mole percent semiaromatic repeat units derived
from one or more monomers selected from
[0076] (i) aromatic dicarboxylic acids having 8 to 20 carbon atoms
and aliphatic diamines having 4 to 20 carbon atoms; and
[0077] (dd) 5 to 50 mole percent aliphatic repeat units derived
from one or more monomers selected from
[0078] (ii) an aliphatic dicarboxylic acid having 6 to 20 carbon
atoms and said aliphatic diamine having 4 to 20 carbon atoms;
and
[0079] (iii) a lactam and/or aminocarboxylic acid having 4 to 20
carbon atoms.
[0080] A preferred Group IV polyamide is PA6T/66.
[0081] Group V polyamides have a melting point of at least
260.degree. C. and comprise
[0082] (ee) greater than 95 mole percent semiaromatic repeat units
derived from one or more monomers selected from
[0083] (i) aromatic dicarboxylic acids having 8 to 20 carbon atoms
and aliphatic diamines having 4 to 20 carbon atoms; and
[0084] (ff) less than 5 mole percent aliphatic repeat units derived
from one or more monomers selected from
[0085] (ii) an aliphatic dicarboxylic acid having 6 to 20 carbon
atoms and said aliphatic diamine having 4 to 20 carbon atoms;
and
[0086] (iii) a lactam and/or aminocarboxylic acid having 4 to 20
carbon atoms.
[0087] A preferred Group V Polyamide is PA6T/DT.
[0088] Group VI polyamides have no melting point and include
poly(hexamethylene isophthalamide/hexamethylene terephthalamide)
(PA6I/6T) and poly(hexamethylene isophthalamide/hexamethylene
terephthalamide/hexamethylene hexanediamide) (PA6I/6T/66).
[0089] In various embodiments the polyamide is a Group I polyamide,
Group II polyamide, Group III polyamide, Group IV polyamide, Group
V polyamide or Group VI polyamide, respectively.
[0090] Preferred polyamides include PA6, PA66, PA610, PA612,
PA6/66, PA6/610, PA6/66/610, PA6/6T, PA610/6T, P612/6T, PA1010,
PA11, PA12 and combinations thereof. More preferred polyamides
include PA6, PA66, PA610, PA612, PA610/6T, PA612/6T, PA1010, PA11,
PA12 and combinations thereof, including PA6, PA612, P612/6T or
PA12, with PA6 most preferred.
[0091] The polyamide component may also be a blend of two or more
polyamides. Preferred blends include those selected from the group
consisting of Group I and Group II polyamides, Group I and Group
III polyamides, Group I and Group VI polyamides, Group II and Group
III polyamides, Group II and Group IV polyamides, Group II and
Group V polyamides, Group II and Group VI polyamides, Group III and
Group VI polyamides, and Group IV and Group V polyamides. A notable
blend is a blend of PA612 and PA612/6T, especially in a blend ratio
of 1:3 of PA612:PA612/6T. See U.S. Patent Application Publication
2012/0196973.
[0092] Polyamides and processes for making them are well known to
those skilled in the art, so the disclosure of which is omitted in
the interest of brevity.
[0093] The polyamide may have a relative viscosity (RV) of 2.5 to
4.0, preferably from 2.6 to 3.5. Relative viscosity is related to
melt viscosity. Varied methods may be used for measured RV values,
and not all commercial polyamides list the RV values. RV is
determined by comparing the time required for a specific volume of
polymer solution to flow through a capillary tube with the
corresponding flow time of the same volume of pure solvent.
Different solvents may be used, depending on the polyamide of
interest. Common solvents include 96% sulfuric acid and 90% formic
acid. For example, the RV of nylon-6 is measured using 1% in 96%
sulfuric acid according to ISO Test Method 307. A similar method
for determining RV is according to ASTM D789.
[0094] Grades of nylon-6 targeted for extrusion (such as
Ultramid.RTM. B33 from BASF) with RV of around 3.3 are suitable.
Molding grades of nylon-6 (such as Ultramid.RTM. B27 from BASF)
with RV of around 2.7 are also suitable for this application.
[0095] The polyamide-ionomer blend further contains 0 to 20 weight
% of pigment; and 0 to 40 weight % of filler; such that the pigment
and/or filler comprises 8 to 50 weight % of the total
composition.
[0096] As used herein pigments have refractive indices greater than
1.8, preferably greater than 2, and particle size less than 0.5
microns such as 0.2 to 0.4 microns. The compositions may comprise
inorganic pigments such as oxide pigments, e.g., titanium dioxide,
zinc oxide, and antimony oxide. Other pigments include lithophone,
chromomolybdic acid, sulfide selenium compound, ferrocyanide and
carbon black pigments. Notably, the pigment comprises titanium
dioxide, zinc oxide, or antimony oxide, preferably titanium
dioxide. The compositions containing inorganic pigments maintain
good flowability and color the molded article even when used in a
small amount.
[0097] As used herein fillers have refractive indices of 1.6 or
less and particle size of 0.8 micron or greater. Suitable fillers
include mineral fillers such as inorganic oxides, carbonates,
sulfates, silicas, alkali and alkaline earth metal silicates, and
barytes of a metal of Groups IA, HA, IIIA, IIB, VIB or VIII of the
periodic table of the elements, including magnesium silicates such
as talc (Mg.sub.3Si.sub.4O.sub.10(OH).sub.2), wollastonite
(CaSiO.sub.3), phyllosilicates (mica) and calcium carbonate.
Notably, the filler comprises an inorganic oxide, carbonate,
sulfate, silica, alkali and alkaline earth metal silicate, or
baryte of a metal of Groups IA, HA, IIIA, IIB, VIB or VIII of the
periodic table of the elements, preferably wherein the filler
comprises calcium carbonate, barium sulfate, wollastonite and talc,
more preferably talc. Fillers may optionally be coated such as with
silane treatments to improve wetting between the filler and the
polymer matrix. The shape, size, and size distribution of the
filler all impact its effectiveness as filler, though, at high
levels, the particular characteristics of the filler become less
important. Preferably the filler particles have a ratio of the
largest dimension to the smallest dimension greater than 5. Fillers
also include glass fibers. Desirably, fillers provide stiffening
(improving Young's modulus ASTM D882) and reduce the coefficient of
linear thermal expansion (ASTM E831) for the composition while
maintaining good elongation to break (ASTM D882). Large particles
such as those having a particle size in at least one dimension
greater than 200 microns such as mica or glass fibers provide good
stiffening but can reduce elongation to break. Particles with at
least one dimension less than 20 microns or less than 5 microns are
preferred. Talc (plate like fillers) and Wollastonite (rod like
fillers) provide for minimizing co-efficient of linear thermal
expansion, maximizing stiffness, while still maintaining a
reasonable amount of elongation to break. Preferably the fillers
are either transparent, such as glass fibers, or white to produce
whiter compositions. For example, talc commercially available as
Jetfine.RTM. 3CA is whiter than Jetfine.RTM. 3CC, which when
incorporated into the polymer matrix leads to a whiter composition.
This is particularly desirable when used in combination with a
white pigment such as titanium dioxide.
[0098] For example but not limitation, the composition may comprise
8 to 20 weight % of pigment such as TiO.sub.2 and 0 weight %
filler, or the composition may comprise 8 to 40 weight % of filler
such as talc and 0 weight % of pigment, or the composition may
comprise 10 to 40 weight % of filler such as talc and 8 to 15
weight % of pigment. Notable compositions comprise or include 8 to
12 weight % of pigment and 12 to 18 weight % of filler such as 10
weight % of pigment and 15 weight % of filler.
[0099] The polyamide-ionomer blend may further contain additional
additives that provide weatherability, stability or improved
processing. The polyamide-ionomer composition or blend can comprise
0.1 to 5 weight % of optional additives, based on the weight of the
total composition. Such additives include stabilizers,
antioxidants, ultraviolet ray absorbers, hydrolytic stabilizers,
antistatic agents, fire-retardants, processing aids such as
lubricants, antiblock agents, release agents, or combinations of
two or more thereof. Of particular note are oxidation inhibitors
(antioxidants), UV stabilizers and hindered amine light
stabilizers. The relative percentages of these additives may be
varied depending upon the particular use of the object desired. The
additives can be added to the polymer blend in typical melt
compounding equipment.
[0100] Suitable stabilizers include antioxidants, such as the
Irganox.RTM. family produced by Ciba-Geigy (now a part of BASF),
and UV stabilizers such as those sold under the Tinuvin.RTM.
tradename by Ciba-Geigy or Cyasorb.RTM. light stabilizer and light
absorber produced by Cytec. Preferred antioxidants are based on
hindered phenols, and preferred UV stabilizers are based on
hindered amine light stabilizers (HALS) such as those sold under
the Chimassorb.RTM. tradename from BASF.
[0101] Lubricants of note include salts of fatty acids such as
sodium stearate or zinc stearate, which may be added at 0.1 to 1
weight % of the total composition.
[0102] The blend may also contain phosphorous salts such as a
hypophosphite salt. Suitable phosphorous salts for use in the
blends are described in greater detail in U.S. Pat. No. 6,399,684.
The salts, including sodium, lithium, or potassium hypophosphite
may be added to the blend composition in 0.1 to 3 weight % of the
composition. Hypophosphite salts may provide improved morphological
or physical properties to the blend such as increased Vicat
temperature and/or improved tensile properties. Of note is a
composition as described herein consisting essentially of (1) a
polyamide as described above; (2) an ionomer as described above;
and (3) hypophosphite salt.
[0103] The polymeric blend composition may be mixed with pigment,
filler and/or additional additives using well known melt mixing
methods employing extruders or other suitable mixers such as
Banbury or Farrel continuous mixers or roll mills.
[0104] Embodiments of the composition include:
The composition wherein the polyamide component comprises nylon 6,
nylon 12, nylon 610, nylon 612, nylon 610/6T, nylon 612/6T, or
combinations thereof. The composition wherein the polyamide
component comprises nylon 6. The composition wherein the comonomer
of (c) is a C.sub.1-C.sub.4 alkyl half ester of maleic acid. The
composition wherein the carboxylic acid functionalities present are
at least partially neutralized to carboxylate salts comprising zinc
or sodium. The composition wherein the carboxylic acid
functionalities present are at least partially neutralized to
carboxylate salts comprising zinc. The composition wherein the
anhydride ionomer component further comprises in combination with
the anhydride ionomer one or more ionomer comprising an E/X/Y
copolymer where E is ethylene, X is a C.sub.3 to C.sub.8
.alpha.,.beta.-ethylenically unsaturated monocarboxylic acid, and Y
is a comonomer selected from alkyl acrylate and alkyl methacrylate
wherein the alkyl groups have from 1 to 8 carbon atoms, wherein X
is present in from 2 to 30 weight % of the E/X/Y copolymer, Y is
present from 0 to 40 weight % of the E/X/Y copolymer, wherein the
carboxylic acid functionalities present are at least partially
neutralized to carboxylate salts comprising one or more alkali
metal, transition metal, or alkaline earth metal cations. The
composition 1 comprising 8 to 20 weight % of pigment and 0 weight %
filler. The composition comprising 8 to 40 weight % of filler and 0
weight % of pigment. The composition comprising 10 to 40 weight %
of filler and 8 to 15 weight % of pigment. The composition
comprising 8 to 12 weight % of pigment and 12 to 18 weight % of
filler. The composition wherein the pigment comprises titanium
dioxide. The composition wherein the filler comprises an inorganic
oxide, carbonate, sulfate, silica, alkali and alkaline earth metal
silicate, or baryte of a metal of Groups IA, IIA, IIIA, IIB, VIB or
VIII of the periodic table of the elements. The composition wherein
the filler comprises calcium carbonate, barium sulfate,
wollastonite or talc. The composition wherein the filler comprises
talc. The composition comprising 10 to 40 weight % of talc and 8 to
15 weight % of titanium dioxide. The composition embodying any
combination of the above embodiments.
[0105] Once the polyamide-ionomer blends are prepared as described
above, they can be further processed into monolayer or multilayer
structures useful as a backsheet for a photovoltaic module. Molten
extruded thermoplastic compositions can be converted into film or
sheet using any techniques known to one skilled in the art.
Suitable additional processes include without limitation blown film
extrusion, cast film extrusion, cast sheet extrusion, lamination,
coextrusion, extrusion coating, and the like. A notable multilayer
backsheet structure may comprise a layer comprising a blend of
polyethylene and ionomer adjacent to the encapsulant layer of the
photovoltaic module.
[0106] Embodiments of the backsheet comprise any of the
compositions described above. Notable embodiments include:
The backsheet wherein the polyamide component comprises nylon 6.
The backsheet wherein the pigment comprises titanium dioxide. The
backsheet wherein the filler comprises calcium carbonate, barium
sulfate, wollastonite or talc. The backsheet wherein the filler
comprises talc. The backsheet wherein the polyamide-ionomer blend
composition comprises 10 to 40 weight % of talc and 8 to 15 weight
% of titanium dioxide.
[0107] A film or sheet can be further oriented beyond its immediate
quenching or casting. The process comprises the steps of
(co)extruding a laminar flow of molten polymers, quenching the
(co)extrudate and orienting the quenched (co)extrudate in at least
one direction. The film may be uniaxially oriented, or it can be
biaxially oriented by drawing in two mutually perpendicular
directions in the plane of the film to achieve a satisfactory
combination of mechanical and physical properties. Orientation and
stretching are well known to one skilled in the art and the
description of which is omitted herein for the interest of
brevity.
[0108] For multilayer structures, the layers may be coextruded or
they may be formed independently and then adhesively attached to
one another to form the backsheet. A backsheet can be made by
(co)extrusion optionally followed by lamination onto one or more
other layers. The backsheet may be fabricated by extrusion coating
or laminating some or all of the layers onto a substrate. For
example, a sheet or film of a core layer may be produced, to which
skin layers and optional tie layers are adhered. Some backsheet
structures contain "e-layers" or layers that have a special
affinity to adhere to the encapsulant. The e-layers can be
co-extruded, or laminated to the subject backsheet composition
through the use of a coextrudable adhesive. However, additional
e-layers are not required to be coated or laminated onto the
instant backsheet structures. The polyamide-ionomer alloys that
comprise the backsheet have strong adhesion to encapsulant layers,
such as the standard commercial EVA encapsulant materials, without
additional e-layers.
[0109] A sheet could be further processed by thermoforming into a
shaped article. In thermoforming, a flat sheet is heated above its
softening point and stretched to the desired shape. For example, a
sheet comprising the polyamide-anhydride ionomer composition could
be thermoformed into a shape that conforms to the shape of the
photovoltaic elements in the photovoltaic cell.
[0110] For use as a backsheet in a photovoltaic module, the
thickness of the sheet is desirably 8 to 20 mils (200 to 500
microns).
[0111] A laminated solar cell module of the invention comprises or
consists essentially of a frontsheet providing a front support
layer formed of a light transmitting material and having first and
second surfaces; a plurality of interconnected solar cells having a
first surface facing the front support layer and a second surface
facing away from the front support layer; a transparent encapsulant
surrounding and encapsulating the interconnected solar cells, the
transparent encapsulant being bonded to the second surface of the
front support layer; and a backsheet as described above wherein one
surface of the backsheet is bonded to the second surface of the
transparent encapsulant.
[0112] The frontsheet or incident layer may be derived from any
suitable sheets or films. Suitable sheets may be glass or polymeric
sheets, such as those comprising a polymer selected from
polycarbonates, acrylics, polyacrylates, cyclic polyolefins (e.g.,
ethylene norbornene polymers), polystyrenes (preferably
metallocene-catalyzed polystyrenes), polyamides, polyesters,
fluoropolymers, or combinations of two or more thereof.
[0113] The term "glass" includes not only window glass, plate
glass, silicate glass, sheet glass, low iron glass, tempered glass,
tempered CeO-free glass, and float glass, but also colored glass,
specialty glass (such as those containing ingredients to control
solar heating), coated glass (such as those sputtered with metals
(e.g., silver or indium tin oxide) for solar control purposes),
E-glass, Toroglass, Solex.RTM. glass (PPG Industries, Pittsburgh,
Pa.) and Starphire.RTM. glass (PPG Industries). Such specialty
glasses are disclosed in, e.g., U.S. Pat. Nos. 4,615,989;
5,173,212; 5,264,286; 6,150,028; 6,340,646; 6,461,736; and
6,468,934. It is understood, however, that the type of glass to be
selected for a particular module depends on the intended use.
[0114] For example, fluoropolymer films, such as
ethylene-tetrafluoroethylene copolymer (ETFE) films, may be used as
frontsheets in photovoltaic modules instead of the more common
glass layers. Another alternative is a film made from a
perfluorinated copolymer resin such as a
tetrafluoroethylene-hexafluoropropylene copolymer (FEP).
[0115] The light-receiving side of the solar cell layer may
sometimes be referred to as a front side and in actual use
conditions would generally face a light source. The
non-light-receiving side of the solar cell layer may sometimes be
referred to as a lower or back side and in actual use conditions
would generally face away from a light source.
[0116] Monocrystalline silicon (c-Si), poly- or multi-crystalline
silicon (poly-Si or mc-Si) and ribbon silicon are the materials
used most commonly in forming the more traditional wafer-based
solar cells. Photovoltaic modules derived from wafer-based solar
cells often comprise a series of self-supporting wafers (or cells)
that are soldered together. The wafers generally have a thickness
of between 180 and 240 .mu.m.
[0117] The solar cell layer may be significantly thicker than the
other layers and irregular in shape and/or thickness, including
spaces between and around the solar cells and other components of
the solar cell layer. In this connection, it should be noted that
the conductors that interconnect the solar cells commonly are
arranged to form stress relief loops to compensate for expansion
and contraction caused by temperature changes. Those loops need to
be encapsulated with the cells. However, when a polymeric backsheet
is used, care must be taken to make certain that the stress loops
will not pierce the backsheet when the several layers are
compressed under heat to form the laminated module. Penetration of
the backsheet by one or more stress loops will promote early
failure of the module, e.g., by short-circuiting resulting from
ingress of moisture at the point(s) of stress loop penetration the
backsheet.
[0118] Therefore, portions of the backsheet laminate will contact
the encapsulant layer outside the perimeter of the solar cell layer
and can be adhered when heat is applied. As used herein, the
perimeter of the solar cell layer is the outline of the outer
limits of the area encompassed by the solar cell layer. In many
cases, it is desirable that the encapsulant material flows into the
spaces and closely encapsulates the solar cells and other
components to physically consolidate the photovoltaic module. Thus,
it may be necessary to apply heat for a period of time sufficient
to allow such flow, which may be longer than that needed for
adhering thinner layers of a more regular shape. For example, heat
may be applied in such a manner that the assembly is maintained
above the softening point of the encapsulant layer for 5 to 30
minutes to effectively consolidate the photovoltaic module.
[0119] The encapsulant layers used in preparing photovoltaic
modules described herein may each comprise a polymeric material
independently selected from olefin unsaturated carboxylic acid
copolymers, ionomers of olefin unsaturated carboxylic acid
copolymers, ethylene vinyl acetate copolymers, poly(vinyl acetals)
(including acoustic grade poly(vinyl acetals)), polyurethanes,
polyvinylchlorides, polyethylenes (e.g., linear low density
polyethylenes), polyolefin block copolymer elastomers, copolymers
of .alpha.-olefins and ethylenically unsaturated carboxylic acid
esters (e.g., ethylene methyl acrylate copolymers and ethylene
butyl acrylate copolymers), silicone elastomers, epoxy resins, or
combinations of two or more thereof.
[0120] The encapsulant layer may preferably comprise a
thermoplastic polymer including ethylene vinyl acetate copolymers,
olefin unsaturated carboxylic acid copolymers, ionomers of olefin
unsaturated carboxylic acid copolymers, and combinations thereof
(for example, a combination of two or more olefin unsaturated
carboxylic acid copolymers, a combination of two or more ionomers
of olefin unsaturated carboxylic acid copolymers, or a combination
of at least one unsaturated carboxylic acid copolymer with one or
more ionomers of unsaturated carboxylic acid copolymers).
[0121] The solar cell module and assembly to prepare it may
optionally further comprise other functional film or sheet layers
(e.g., dielectric layers or barrier layers) embedded within the
module. Such functional layers may be derived from any of the above
mentioned polymeric films or those that are coated with additional
functional coatings. For example, poly(ethylene terephthalate)
films coated with a metal oxide coating, such as those disclosed in
U.S. Pat. Nos. 6,521,825 and 6,818,819 and European Patent
EP1182710, may function as oxygen and moisture barrier layers in
the laminates.
[0122] If desired, a layer of nonwoven glass fiber (scrim) may also
be included between the solar cell layers and the encapsulants to
facilitate deaeration during the lamination process or to serve as
reinforcement for the encapsulants. The use of such scrim layers is
disclosed in, e.g., U.S. Pat. Nos. 5,583,057; 6,075,202; 6,204,443;
6,320,115; and 6,323,416 and European Patent EP0769818.
[0123] In addition, metal films, such as aluminum foil or metal
sheets, such as aluminum, steel, galvanized steel, or ceramic
plates may be utilized in addition to the polymeric backsheet
described herein as backing layers for the photovoltaic module.
[0124] A special film or sheet may be included to serve both the
function of an encapsulant layer and an outer layer. It is also
conceivable that any of the film or sheet layers included in the
module may be in the form of a pre-formed single-layer or
multilayer film or sheet.
[0125] If desired, one or both surfaces of the incident layer films
and sheets, the backsheet films and sheets, the encapsulant layers
and other layers incorporated within the solar cell module may be
treated prior to the lamination process to enhance the adhesion to
other laminate layers. This adhesion enhancing treatment may take
any form known in the art and includes those set forth in U.S.
Patent Application Publication 2010/0108126.
[0126] Manufacturing the solar cell module comprises providing a
front support layer formed of a light transmitting material and
having front and back surfaces; placing a first transparent
thermoplastic encapsulant layer adjacent to the back surface of the
front support layer; positioning a plurality of interconnected
solar cells having first and second surfaces so that the first
surfaces thereof are adjacent to the first transparent encapsulant
layer; placing a second transparent thermoplastic encapsulant layer
adjacent to the second surfaces of the solar cells; placing a
backsheet as described above adjacent to the second transparent
thermoplastic encapsulant layer to thereby form an assembly;
subjecting the assembly to heat and pressure so as to melt the
encapsulant layers and cause the encapsulant to surround the solar
cells, and cooling the assembly so as to cause the encapsulant to
solidify and bond to the front support layer, the solar cells and
the backsheet, thereby laminating the layers and the solar cells
together to form an integrated solar cell module.
[0127] The photovoltaic module is prepared by providing an assembly
for conversion under heat and pressure into a laminated solar cell
module, the assembly comprising a front support layer formed of a
light transmitting material and having front and back surfaces; a
first transparent thermoplastic encapsulant layer adjacent to the
back surface of the front support layer; a plurality of
interconnected solar cells having first and second surfaces
adjacent to the first transparent encapsulant layer; a second
transparent thermoplastic encapsulant layer disposed adjacent to
the solar cells in parallel relation to the first transparent
encapsulant layer; and a thermoplastic backsheet layer as described
above.
[0128] A vacuum laminator may be used to adhere the layers of the
assembly together to provide the photovoltaic module. The laminator
comprises a platen base, on which the layers of the assembly are
placed in overlaying fashion for lamination. The laminator also
comprises an enclosure that covers and completely surrounds the
platen base. The region enclosed by the platen and enclosure may be
evacuated. The laminator also comprises a flexible bladder within
the enclosure attached to the top inner surface of the enclosure,
which may be inflated to a pressure greater than the pressure in
the evacuated region. For example, the pressure above the bladder
may be atmospheric and the laminate may be held under vacuum
beneath the bladder to remove air. When the bladder is inflated,
the flexible surface of the bladder is pushed from the top of the
enclosure toward the platen and applies a surface pressure to the
multilayer assembly to ensure a good thermal contact between the
assembly and the platen. For lamination of the module, the
laminator is preheated to a temperature above the softening
temperature of the encapsulant layer(s) and held at that
temperature throughout the lamination process.
[0129] Heat-resistant sheets may be placed under the assembly to
retard heat flow and allow deaeration and devolatilization of the
sample. Release sheets may be placed under the and/over the
assembly to prevent the sample layers from adhering to parts of the
laminator. The assembly is placed on the platen and the enclosure
of the laminator is lowered into place and sealed. Next, the region
surrounding the assembly between the platen and enclosure of the
laminator is evacuated (e.g. to a pressure of 1 mbar) to help
further with the prevention of voids, defects, and air pockets.
Next, the rubber bladder is inflated (e.g. to a pressure of 999
mbar) so that it presses against the assembly and ensures good
thermal contact with the platen. The pressure and heat are
maintained for a sufficient period of time (for 1 to 10 minutes) to
soften the encapsulant layers and adhere to solar cells and the
adjoining layers.
[0130] When the heating step is complete, the bladder is
depressurized to 0 mbar so that it may be removed from contact with
the multilayer film laminate, the enclosure is vented to
atmospheric pressure and the enclosure is unsealed and opened. The
multilayer film laminate is removed from the platen and allowed to
cool to room temperature.
[0131] The lamination methodology described here is by no means the
only possible way to carry out such laminations. For example, more
advanced laminators have retractable pins that hold the multilayer
laminate structure above the heat source until the desired time to
effect contact and heating. This would obviate the need for heat
resistant layers in most cases.
EXAMPLES
Materials Used
[0132] AI-1: A copolymer of ethylene, 11 weight % of methacrylic
acid and 6 weight % of ethyl hydrogen maleate, neutralized with Zn
cations to a level of 50-60%, MI of 0.1 g/10 min AI-2: an anhydride
ionomer terpolymer comprising ethylene, 13 weight % of acrylic acid
and 4 weight % of ethyl hydrogen maleate neutralized with Zn
cations to a level of 50%. ION-1: A copolymer of ethylene and 19
weight % of methacrylic acid, neutralized with Zn cations to a
level of about 36%, MI of 1.3 g/10 min ION-2: A copolymer of
ethylene and 15 weight % of methacrylic acid, meutralized with Zn
cations to a level of about 60%, MI of 0.7 g/10 min PA-6: nylon-6
homoploymer available commercially as Ultramid.RTM. B27E from BASF.
PA-12A: nylon-12 homopolymer available commercially as Rilsan.RTM.
AMNO from Arkema. PA-12B: nylon-12 homopolymer available
commercially as Rilsan.RTM. AESNO from Arkema. PA-612/6T:
nylon-612/6T copolymer available from DuPont under the tradename
Zytel.RTM.. Tie-1: a maleic anhydride modified linear low density
polyethylene (LLDPE), with density of 0.91 g/cm.sup.3 and melt
index of 1.7 g/10 min, commercially available from DuPont. Tie-2: a
maleic anhydride modified linear low density polyethylene (LLDPE),
with density of 0.91 g/cm.sup.3 and melt index of 2.7 g/10 min,
commercially available from DuPont. Tie-3: a maleic anhydride
modified linear low density polyethylene (LLDPE), with density of
0.91 g/cm.sup.3 and melt index of 3.1 g/10 min, commercially
available from DuPont. TiO.sub.2: titanium dioxide commercially
available from DuPont as Ti-Pure.RTM. R105 or comparable material.
TiO.sub.2 Concentrate: 70 weight % titanium dioxide pre-dispersed
in ethylene methacrylate copolymer commercially available as 111676
White COP MB from Ampacet (660 White Plains Road, Tarrytown, N.Y.
10591). ZnO Concentrate: 45 weight % zinc oxide pre-dispersed in
ethylene methacrylic acid copolymer. Fillers used are summarized in
the following table.
TABLE-US-00001 bulk true Particle Diameter Length density density
Filler material Commercial designation shape (.mu.m) (.mu.m)
(kg/m.sup.3) (kg/m.sup.3) F1 wollastonite Nyglos .RTM. 8 rod 12 156
480 2900 F2 coated wollastonite Nyglos .RTM. 8 10012 rod 12 156 480
2900 F3 wollastonite Nyglos .RTM.G rod 55 825 720 2900 F4 mica
Suzorite .RTM. 60S platy 150-500 176-291 2700 F5 glass fibers
Chopvantage .RTM. HP3660 fiber 10 3000-4000 2460 F6 talc Jetfine
.RTM. 3CA White 1 platy F7 talc Jetfine .RTM. 3CC Tan 1 platy F8
talc Luzenac .RTM. HAR-T84 platy 2
Additives used are summarized in the following table.
TABLE-US-00002 Commercial Additive function material designation
Add1 lubricant zinc stearate Commercial grade Add2 UV absorber
oxanilide Tinuvin .RTM. 312 Add3 UV light HALS Tinuvin .RTM. 770
stabilizer Add4 UV light HALS Chimassorb .RTM. 440 stabilizer Add5
antioxidant phenolic antioxidant Irganox .RTM. B1171 and phosphite
Add6 antioxidant phenolic antioxidant Irganox .RTM. 1010 Add7
antioxidant phenolic antioxidant Irganox .RTM. B215 and phosphite
Add8 processing trisarylphosphite Irgafos .RTM. 168 stabilizer Add9
antioxidant phenolic antioxidant Irganox .RTM. 1098 Add10 UV light
HALS Chimassorb .RTM. 944 stabilizer Add11 UV absorber Oxanilide
Tinuvin .RTM. 234 Add12 processing Sodium hypophosphite Commercial
grade stabilizer Add13 lubricant Zinc stearate Commercial grade
[0133] Several commercial backsheet structures were evaluated as
standards:
HRPET: Hydrolysis resistant PET, 12 mil thickness, commercially
available as PYE3000 from Coveme SPA, Bologna, Italy. TPT:
Tedlar.RTM./PET/Tedlar.RTM., 12 mil thickness, commercially
available as Icosolar.RTM. 2442 from Isovoltaic AG, Leibring,
Austria or 1200 Dun-solar TPT backsheet, commercially available
from DUNMORE Corporation, 145 Wharton Rd., Bristol, Pa. 19007. APA:
A three-layer sheet comprising a core layer comprising polyester
and two skin layers comprising modified polyamide, commercially
available as Icosolar.RTM. APA 4004 from Isovoltaic AG, Liebring,
Austria. AAA: A three-layer sheet comprising a core layer
comprising modified polyamide and two skin layers comprising
modified polyamide, commercially available as Icosolar.RTM. AAA
3554 from Isovoltaic AG, Liebring, Austria.
[0134] Blends of materials listed above were prepared by melt
blending following the procedure described or similar processes.
Compounding was done using a 25 mm 38/1 L/D ZSK-25 World Lab
twin-screw extruder comprised of nine 100 mm long barrels
manufactured by Krupp Werner & Pfleiderer (Coperion) or similar
processes. The polymers were pre-blended and then fed to the throat
of the extruder (barrel 1) using a K-tron.RTM. loss-in-weight
feeder. The fillers were fed using a second K-tron.RTM. feeder to
the extruder using a side feeder at Barrel 4. There was a vacuum
pulled on the melt before and after addition of the filler (at
barrel 4 and barrel 8). The melt blend exiting the extruder die
face (after barrel 9) was die face-cut using a Gala cutter.
[0135] Operating conditions for Comparative Example C4 in Table 2
are shown in Table 1. Other examples were prepared similarly.
TABLE-US-00003 TABLE 1 Set Point (.degree. C.) Actual (.degree. C.)
Temperature Control Zone 1 uncontrolled (Barrel 1 feed) Temperature
Control Zone 1 260 260 (Barrel Zones 2 and 3) Temperature Control
Zone 2 260 260 (Barrel Zones 4 and 5) Temperature Control Zone 3
260 260 (Barrel Zones 6 and 7) Temperature Control Zone 4 260 257
(Barrel Zones 8 and 9) Temperature Control Zone 5 260 257 (Die)
Screw RPM 300 Torque % 53% Die pressure (Mpa) .sup. 5.3 (770 psig)
Melt Temperature .degree. C. 297 Feed rate polymer 95 gpm Feed rate
filler 40 gpm Vacuum (mm Hg) Zone 4 and 8 51 KPa (15 in Hg)
[0136] The compositions of the melt blends are shown in Table
2.
TABLE-US-00004 TABLE 2 Filler Example Loading PA6 ION-2 AI-1 F1 F2
F3 F4 C1 0% 60% 40% C2 0% 60% 40% C3 15% 51% 34% 15% 1 15% 51% 34%
15% C4 30% 42% 28% 30% 2 30% 42% 28% 30% 3 40% 36% 24% 40% 4 30%
42% 28% 30% 5 40% 36% 24% 40% C5 15% 51% 34% 15% 6 15% 51% 34% 15%
C6 30% 42% 28% 30% 7 30% 42% 28% 30%
[0137] The collected pellets were dried overnight at 70 to
85.degree. C. in an air-circulating Blue M tray dryer oven that was
fitted with a nitrogen purge. Each of the dried polymer samples
were used to cast 8-inch (228 mm) wide, nominally 0.33 to 0.35 mm
thick sheets. Sheets were cast using a 31.75-mm diameter 30/1 L/D
single screw extruder, built by Wayne Machine (Totowa, N.J.),
fitted with a 3/1 compression ratio, single-flight screw with 5 L/D
of a melt mixing section. The extruder die was a 203-mm wide coat
hanger type flat film die with a 0.35 mm die gap. The molten
polymer film exiting from the die was cast onto a 203-mm wide by
203-mm diameter double shell spiral baffle casting roll fitted with
controlled temperature cooling water. The casting roll and die were
built by Killion Extruders (Davis Standard, Cedar Grove, N.J.).
Extruder conditions typical for the compositions are provided in
Table 3.
TABLE-US-00005 TABLE 3 Extruder Conditions Set Point (.degree. C.)
Actual (.degree. C.) Barrel Zone 1 240 240 Barrel Zone 2 240 240
Barrel Zone 3 240 240 Barrel Zone 4 240 240 Filter Flange 240 240
Adapter 240 240 Die End 245 245 Flat Die 240 240 Melt Temp (before
filter) 237 Melt Temp (after filter) 240 Melt Press (MPa) before
filter 4.6 (670 psig)
[0138] The 0.35-mm thick polymer sheets were used to test
properties relevant to PV backsheets.
Test Methods
[0139] Ash: Samples were weighed into a crucible and heated for 15
minutes in an 800.degree. C. muffle furnace. The reported number
represents the % of sample remaining in the crucible. This test was
used to verify that the proper loading of filler was achieved.
[0140] Tensile Properties (ASTM D882-12) were measured on 25 mm by
150 mm coupons die cut from the sheet. Five coupons were oriented
so that the long direction was in the machine direction (MD) and
five coupons were oriented so that the long direction was in the
transverse direction (TD). Coupons were conditioned at 50% RH and
23.degree. C. for at least seven days prior to testing at 50% RH
and 23.degree. C. The gage length was 25 mm and the cross-head
speed was 508 mm/min. The reported results are the average of five
coupons. A combination high Young's Modulus (measure of stiffness)
and at least 100% elongation (higher elongation suggests better
toughness) to break is preferred.
[0141] Coefficient of Linear Thermal Expansion (ASTM E813-13) was
measured on 4.9 by 65 mm coupons die cut from the sheet. Three
coupons were oriented so that the long direction was in the MD and
three coupons were oriented so that the long direction was in the
TD. Coupons were conditioned at 50% RH and 23.degree. C. for at
least seven days prior to testing. The thermal mechanical analyzer
was set up with the film fiber probe and a 0.1 N preload force was
applied. Specimens were cooled to -60.degree. C. prior to the start
of the run and the heated a rate of 5.degree. C./min to 90.degree.
C. The slope of the best fit linear line between -60.degree. C. and
90.degree. C. was taken as CLTE (.mu.m/m/.degree. C.). Two test
results in each orientation are reported. A lower coefficient of
linear thermal expansion is preferred so that the thermoplastic
backsheet expands and contacts the encapsulant layer.
[0142] Moisture Vapor Transmission Rate (MVTR) at 38.degree. C. and
100% RH was measured on coupons cut from sheet according to ASTM
F1249.
[0143] Moisture Vapor Transmission Rate (MVTR) at 85.degree. C. and
100% RH was measured on a Permatran 3/33 model using a Yamato
DKN402 oven. ASTM F1249-06, was followed except the temperature was
85.degree. C.
[0144] Moisture Uptake at 50% RH and 23.degree. C. or water
immersion at 85.degree. C. This test measured the amount of water
absorbed into a sheet sample (typically 25 mm wide by 150 mm long)
die cut from the sheet after the indicated exposure condition.
Moisture absorbed was determined by Karl Fischer titration as per
ASTM D6869-03 (150.degree. C. oven temperature).
[0145] Shrinkage after heat treating for 30 minutes in
air-circulating oven at 150.degree. C. Rectangles were scissor cut
from the sheet. Samples were allowed to condition at 50% RH and
23.degree. C. for at least seven days prior to measuring sheet
dimension in MD and TD. Samples were then suspended by a hook in a
pre-heated air circulating oven at 150.degree. C. for 30 minutes
after which the sheet samples were removed from the oven allowed to
condition for at least 48 hours at 50% RH and 23.degree. C. before
the MD and TD lengths were measured again. Changes in dimension are
reported as the percent reduction in the dimension as a result of
conditioning at 150.degree. C.
[0146] Color Measurement (ASTM E1347-06) Color of samples was
measured using a Hunter Lab Colorquest XE Colorimeter (L*, a*, b*).
L* is a measure of whiteness; whiter materials have higher L*
values.
[0147] Summaries of the test results are given in Tables 4 and
5.
TABLE-US-00006 TABLE 4 Tensile properties CLTE (ASTM D882-12)
(.mu.m/m/.degree. C.) Young's Strain at MD TD Modulus (ksi) break
(%) Sample Sample Sample Sample MD TD MD TD 1 2 1 2 C1 82.8 83.6
507 451 248 232 232 225 C2 100 79 484 451 C3 154 102 458 428 152
144 224 244 1 118 101 431 298 C4 249 108 162 19 2 181 125 12.6 16.2
3 194 138 3.8 5.4 4 261 114 64 20.8 5 171 161 3.8 4.8 C5 117.9 114
73.7 36 142 126 136 152 6 114.9 107.8 91 50 C6 178.8 177 9 6.6 7
163 141 9 8.2
[0148] The test results in Table 4 show that adding fillers
increased stiffness as measured by a higher Young's modulus and
reduced toughness as measured by elongation or strain at break.
Fillers also reduced the Coefficient of Linear Thermal Expansion
and on a weight basis, bigger rodlike or platelike fillers reduce
CLTE more. Comparative Example C1 contained no filler and had CLTE
greater than 200 .mu.m/m/.degree. C. Comparative Example C3
containing 15 weight % of wollastonite had an MD CLTE of less than
155 .mu.m/m/.degree. C. and Comparative Example C5 containing 15
weight % mica had an MD CLTE of less than 142 .mu.m/m/.degree.
C.
TABLE-US-00007 TABLE 5 Water Uptake at 23.degree. C. shrinkage MVTR
at 38.degree. C. at in at 150.degree. C. g-mm/m.sup.2/day
g-mm/m.sup.2/day 50% RH water MD TD Sample 1 Sample 2 % % % % C1 95
99 2.5 7.3 0 0.3 C2 64 62 2.4 6.4 0.5 0.6 C3 72 70 5.6 0.2 1 1 62
61 5.3 0.5 0.7 C4 48 40 1.6 5.3 0.1 0.7 2 67 69 4.7 0.2 0.3 3 4.8
0.1 0.7 4 43 41 1.7 4.9 0 0.3 5 330 366 1.4 4.7 0 0 C5 54 51 2 5.4
0.5 0.3 6 63 63 2.1 5.6 0.2 0.3 C6 32 32 1.6 4.7 0.4 0 7 65 67 1.6
4.7 0 0
[0149] As shown in Table 5, the addition of fillers tended to
reduce the moisture vapor transmission rate, with some exceptions.
Example 5 contained 40 weight % of mica and had a very high MVTR
(higher than the sample that contained no filler). With small
rod-shaped fillers, the polyamide-anhydride ionomer examples had
lower MVTR than comparable polyamide-conventional ionomer
compositions. With mica filler, the opposite was observed. The
addition of filler can result in a reduction of the moisture
uptake. In terms of shrinkage of the sheet after 30 minutes at
150.degree. C., all of the samples had very low shrinkage (with or
without filler). These shrinkage numbers are very close to the
error in the measuring device.
[0150] The results in Tables 4 and 5 suggested bigger filler types
(like fiberglass or mica) were better at reducing sheet CLTE and
increasing sheet stiffness but resulted in very low elongation to
break and had negative effect on moisture transmission.
[0151] Additional blends were prepared with additives as shown in
Table 6.
TABLE-US-00008 TABLE 6 Blend A B C* D* E F* G H I J Material Weight
% Blend A 83.9 73.9 Blend C 90 85 PA-6 60 0 60 60 39.23 PA-12A 0 22
0 PA-12B 0 33 0 AI-1 40 45 0 40 ION-1 40 31.36 ION-2 35.7 HDPE
53.54 ZnO 1.7 Conc. TiO.sub.2 15 15 10 10 15 Talc 10 15 F6 10 Add1
0.7 Add2 0.2 Add3 0.15 0.6 Add5 0.2 0.3 0.28 Add6 0.1 0.15 0.15
Add7 0.15 Add8 0.1 Add10 0.31 0.7 Add11 0.35 Add12 0.13 Add18 1.1
*Commercially available from LTL Color Compounders, Inc. 20
Progress Drive, Morrisville, PA 19067. Additional UV stabilizer and
antioxidant additives may also be present (not included in the
weight %).
[0152] The blends in Table 6 were combined and melt blended with
additional materials to provide polyamide-ionomer compositions
summarized in Table 7 useful for PV backsheets. Other fillers were
included such as talc. Example 10 has no filler but has 21.5 weight
% of TiO.sub.2 Concentrate as a pigment.
TABLE-US-00009 TABLE 7 Filler Blend TiO.sub.2 Loading A C G
Concentrate F6 F7 Add2 Add3 Add5 L* a* b* C7 0 100 C8 30 70 30 8 30
70 30 C9 15 85 15 9 15 85 15 10 77.7 21.5 0.2 0.6 0.3 89.3 -0.2 3.3
11 15 84.2 15 0.2 0.6 0.3 47.5 1.1 3.1 12 25 74.3 25 0.2 0.6 0.3
58.6 -1.3 3.9 13 15 70.1 14.2 15 0.2 0.6 0.3 84.6 -0.9 3.3
[0153] The color of pellets of Compositions 10-13 was measured and
the values indicated in Table 7. Compositions using talc filler F6
were whiter than with talc filler F7 as indicated by L*.
[0154] Tables 8 and 9 list the property tests on the sheet
samples.
TABLE-US-00010 TABLE 8 Tensile properties (ASTM D882-12) CLTE
(.mu.m/m/.degree. C.) Young's Modulus (MPa) Strain at break (%) MD
TD MD TD MD TD Sample 1 Sample 2 Sample 1 Sample 2 C7 548 566 560
533 212 202 194 205 C8 1426 1197 200 186 80 77 96 97 8 1257 1248
326 297 C9 963 856 377 395 126 112 151 138 9 944 783 453 440 HRPET
2141 2158 135 114 588.1 584.5 205 224.8 TPT 3123 3241 101 81 33.08
33.96 25.15 25.8
[0155] The test results in Table 8 show that smaller platelike
fillers like talc can be added to the polyamide-ionomer blend at
loadings as high as 30 weight % to reduce the CLTE and still
maintain at least 100% elongation to break. Polyamide-anhydride
ionomer compositions had roughly comparable stiffness and better
strain at break than comparable polyamide-conventional ionomer
compositions. The compositions had lower Young's modulus and higher
strain at break than commercial backsheet materials.
TABLE-US-00011 TABLE 9 MVTR at 38.degree. C. Water uptake at
23.degree. C. shrinkage at 150.degree. C. Ash Test
(g-mm/[m.sup.2-day]) at 50% RH in water MD TD Sample 1 Sample 2
Sample 1 Sample 2 % % % % C7 2 2 9.24 9.62 2.2 6.3 0.7 0.7 C8 31 31
1.88 1.88 1.4 4.2 0.2 0.5 8 30 30 1.75 1.75 1.5 4.4 0.1 0.5 C9 16
16 3.88 4.11 1.8 5.0 0.2 0.3 9 16 16 3.15 3.20 1.8 4.6 0.6 0.5
HRPET 0.786 0.2 1.4 1.0 0.3 TPT 0.786 0.3 0.5 0.2 0.0
[0156] In Table 9, significant reductions in MVTR and moisture
absorption were seen when fillers were added to the
polyamide-ionomer blends. Example 8 and Comparative Example C8
contained 30 weight % talc and had MVTR of 75 or less and moisture
absorption of less than 4.5 weight % at 85.degree. C. compared to
the non-filled blend (C7) that had an MVTR of over 300
g-mil/m.sup.2/day and moisture absorption at 85.degree. C. of 6.3%.
Polyamide-anhydride ionomer compositions had roughly comparable
water uptake and lower MVTR than comparable polyamide-conventional
ionomer compositions.
[0157] The next comparison illustrates that under equivalent
compounding conditions, better mechanical and thermal properties
were obtained when the mineral filler was added to a nylon-6
polyamide-anhydride ionomer alloy compared to adding the mineral
filler to a nylon-6 polyamide-standard ionomer alloy.
TABLE-US-00012 TABLE 10 Weight % Thickness of sheet PA-6 ION-2 AI-1
Add8 Add9 F7 (mm) C10 44.80 30 0.10 0.1 25 0.35 10 44.80 30 0.10
0.1 25 0.34
[0158] The tensile properties were measured on film samples
conditioned for one week at 23.degree. C. and 50% RH and summarized
in Table 11. Moisture permeation, uptake and damp heat aging are
also summarized in Table 11.
TABLE-US-00013 TABLE 11 C10 10 MD TD MD TD Tensile properties
Young's Modulus 1113 938 1150 896 (ASTM D882-12) (MPa) Strain at
break (%) 136 42 319 280 CLTE (.mu.m/m/.degree. C.) 83.5 129 72.5
102 MVTR at 38.degree. C. Transmittance 6.05 5.84 (g/[m.sup.2-day])
Permeation 2.13 1.97 (g-mm/[m.sup.2-day]) Water uptake At 50% RH
(%) 1.4 1.3 at 23.degree. C. 1 week in water (%) 4.6 4.5 Strain
Strain Young's at Young's at Modulus break Modulus break Damp heat
aging After 929 186 853 319 at 85.degree. C. and 72 hours 100% RH
After 1001 51 1020 258 1000 hours After 1028 50 1252 178 2000
hrs
[0159] As shown in Table 11, Young's Modulus was comparable for
both compositions but the strain at break was significantly higher
for the polyamide-anhydride ionomer composition. The coefficient of
linear thermal expansion was lower in both MD and TD for the
polyamide-anhydride ionomer composition. The permeation rate was
lower with the polyamide-anhydride ionomer composition. The
moisture pick-up after 1 week at 50% RH or 1 week immersed in water
was slightly lower with the polyamide-anhydride ionomer
composition.
[0160] Table 11 also records the stiffness (Young's modulus) and
elongation (strain at break) for the MD-oriented coupons after 72,
1000 and 2000 hours of damp heat conditioning. The mineral-filled
alloy based on the polyamide-anhydride ionomer composition produced
better hydrolysis resistance to damp heat aging than the one
prepared with a conventional ionomer. The polyamide portion of the
polyamide-ionomer alloy was presumably undergoing further
crystallization under the 85.degree. C. and 100% RH conditioning so
the observed stiffness (Young's Modulus) increased with time.
Because hydrolysis and/or thermal degradation were also occurring
there was a reduction in the amount of elongation in the coupon
before it broke. The coupons from the anhydride ionomer-polyamide
composition exhibited much better retention of elongation to break
over this 2000-hour conditioning period.
[0161] Three-layer coextruded backsheet structures were prepared
with the structures summarized in Table 12. The term "outer skin"
refers to the layer of the backsheet structure that would face
outward in the photovoltaic module, the term "core" refers to a
layer inside the backsheet structure, and the term "inner skin"
refers to the layer of the backsheet that would face the
encapsulant layer of the photovoltaic module. The three-layer
sheets were prepared from 15 weight % TiO.sub.2-filled and 10
weight % talc-filled polyamide-ionomer compositions. The sheets
were cast on a three layer coextrusion sheet line with nominally
0.002-inch (0.05 mm) thick skin layers and 0.010-inch (0.25 mm)
thick core layers. The sheet structures are given in Table 12.
TABLE-US-00014 TABLE 12 Outer skin layer Core layer Inner skin
layer C11 Blend F Blend C Blend F C12 Blend F Blend D Blend F 11
Blend F Blend A Blend F C13 Blend C Blend D Blend C 12 Blend C
Blend A Blend C 13 Blend E Blend B Blend E
[0162] Tables 13 and 14 report the test results on the three-layer
sheets.
TABLE-US-00015 TABLE 13 Tensile properties (ASTM D882-12) Young's
Strain CLTE Modulus (MPa) at break (%) (.mu.m/m/.degree. C.) MD TD
MD TD MD TD C11 717 703 495 505 144.6 153.6 C12 800 727 446 459
114.1 138.3 11 624 591 414 470 186.9 210.6 C13 816 770 462 444 48.8
125.5 12 619 639 502 472 13 627 577 395 503 175.5 199.2 HRPET 2141
2158 135 114 586.3 227.9 TPT 3123 3241 101 81 33.5 25.5
TABLE-US-00016 TABLE 14 Water uptake at 23.degree. C. shrinkage at
150.degree. C. Thickness MVTR at 85.degree. C. At 50% RH At 100% RH
MD TD (mil) (mm) g/[m.sup.2-day]) (g-mm/[m.sup.2-day]) % % % % C11
14.5 0.368 250.93 92.33 1.7 5.6 0.5 0.9 C12 13.9 0.353 213.68 75.43
1.6 4.8 0.1 0.5 11 1.8 5.8 0.0 0.7 C13 1.6 4.8 0.2 0.3 12 1.9 6.1
0.0 0.7 13 15.6 0.396 85.84 33.99 0.9 2.1 0.1 0.7 HRPET 12 0.305
0.2 1.4 1.0 0.3 TPT 13 0.330 36.5 12.04 0.3 0.5 0.2 0.0
[0163] Example 13 showed very good (low) water vapor transmission
and uptake compared to Comparative Examples C11 and C12.
[0164] The following General Procedure was used to laminate
backsheet materials to glass and encapsulant sheets to test the
properties of a photovoltaic module. For these tests no
photovoltaic layer was included, but laminations with photovoltaic
layers could be performed similarly.
[0165] Glass: 4-mm thick annealed glass from Kingston Plate and
Glass (Kingston, Ontario Canada)
[0166] Encapsulant sheet: 0.015 inch thick EVA (ethylene vinyl
acetate copolymer encapsulant sheet (Photocap.RTM. 15420 or 15295
sold by STR Corporation, 18 Craftsman Road, East Windsor, Conn.
06088 USA)
General Procedure for Fabricating Glass/Encapsulant/Backsheet
Laminates
[0167] Rectangles of Glass/Encapsulant/Backsheet [2.5 inch by 5
inch (62 by 125 mm) or 5 inch by 5 inch (125 by 125 mm)] were
laminated. The backsheet samples were dried overnight under vacuum
at 30.degree. C. prior to laminating. The glass was washed with
soapy water and the layers assembled as follows:
glass/encapsulant/backsheet/10 mil thick fluoropolymer coated
cloth/0.25-inch silicone rubber. If the backsheet contained an
inner skin layer, that layer was in contact with encapsulant.
One-inch (25 mm) wide tabs of fluoropolymer-coated release sheet
were placed between the glass and the encapsulant and the
encapsulant and the backsheet. The inclusion of fluoropolymer
release sheets provided a tab between glass and encapsulant or
backsheet and encapsulant to initiate subsequent peel testing on
laminated glass. The assembly was placed in a 12 inch by 9 inch
(300 mm by 225 mm) vacuum bag (Tyvek.RTM. barrier bag Part number
SI-BA-7033, supplied by Smith Induspac Ltd 140 Iber Road,
Stittsville, Ontario, Canada K2S 1E9). The assembly was vacuum
sealed in the bag using a Promarks TC-420LC vacuum sealer
(Promarks, Inc., 1915 E. Acacia Street, Ontario, Calif. 9176, USA)
with 60 seconds of vacuum prior to heat seal, seal time 2 seconds,
cooling time 2.1 seconds. The layers were thermally bonded together
by placing the vacuum-bagged assembly in a preheated
air-circulating oven set at 150.degree. C. for 30 minutes. A 2.6 kg
aluminum block was placed on top of the vacuum bag to improve the
consistency of the glass laminate. The glass side of the laminate
was down during the thermal bonding. After 30 minutes in the oven,
the vacuum bag assembly was removed and allowed to cool 10 minutes
before cutting open the bag and removing the laminate.
[0168] Adhesion: Peel tests were performed using 4 inch/minute (100
mm/min crosshead speed after conditioning at 23.degree. C., 50% RH.
The glass is held in place by the stationary jaw on the test
machine. A tab from the backsheet is gripped in the moving jaw.
Test results are reported as the average of four peels for each
material. Table 15 reports the average peel strength between the
weakest interface (backsheet to encapsulant) or (encapsulant to
glass).
TABLE-US-00017 TABLE 15 Adhesion to Encapsulant lb-f/in N/cm
Location of peel C11 32 56 Backsheet to encapsulant C12 40 70
Combination of backsheet to encapsulant and glass to encapsulant 11
40.5 71 Backsheet to encapsulant C13 13 23 Backsheet to encapsulant
HRPET 10 18 Backsheet to encapsulant TPT 21 37
Glass-encapsulant
[0169] These peel strength numbers demonstrate a strong bond
between backsheet and encapsulant which confirms the
polyamide/ionomer alloy sheet does not require any special surface
treatment to achieve a strong bond to the EVA based
encapsulant.
[0170] Test sheets were also fabricated into small photovoltaic
modules having a 2.times.2 array of solar cells. The components are
listed in Table 16. The materials were laid up in the proper
positions to prepare a functional photovoltaic module and laminated
using a Meier vacuum laminator with lamination conditions of
145.degree. C., for fifteen minutes, evacuation 3 minutes and press
for 11 minutes.
TABLE-US-00018 TABLE 16 Material Brand Code EVA Revax R767-0.45 mm
thickness Solar cell JA Mono-125SOR22B 17.6-17.8% Solder Ribbon
Sveck Sn62 Pb36 Ag2 Glass AGC Japan Solar grade --temper
glass--low-Iron A1 Frame Haida 304 .times. 284 .times. 25 mm
Junction Box Renhe PV-RH06-60 Seal silicon Tonsan PV1527 Flux Asahi
ANX-3133
Testing after Sheets were Used to Fabricate Mini Solar Modules
[0171] Damp heat: Two modules of each state were exposed to
85.degree. C./85% RH for after 0, 1000 and/or 2000 hours of damp
heat exposure. Changes in color on the front side (color through
the glass) and back side of module were measured as described
above.
[0172] UV testing: Using the IEC 61215 UV preconditioning standard
(3% UVB), one module was exposed from the front and one from the
back. Tests were conducted after 0, 1, 2, 3, 4 and 5 times the IEC
standard duration.
[0173] Thermal cycling (TC): Two modules of each state were exposed
to cycles of -40.degree. C. to 85.degree. C. per the IEC 61215
standard. Standard properties (see below) were measured after 0,
200, 400 and 600 cycles.
[0174] Thermal cycling-humidity freeze (TC-HF): Two modules of each
state were exposed to the IEC 61215 protocol of 50 cycles thermal
cycling (-40.degree. C. to 85.degree. C.) followed by 10 cycles of
humidity freeze (-40.degree. C. to 85.degree. C. at 85% RH).
Standard properties after 0, 1, 2 and 3 intervals of 50 thermal and
10 humidity freeze cycles were measured. Testing was done after the
humidity freeze portion of the cycling. In the Tables below, the
number of each type of cycle is indicated.
[0175] Table 17 reports testing on mini modules that were
fabricated using the backsheets in Table 12.
TABLE-US-00019 TABLE 17 Crack behavior Change in module color after
1000 hours damp heat treatment after after after .DELTA.L* front
.DELTA.L* back .DELTA.b* front .DELTA.b* back 150TC/20HF TC400
TC150/HF30 C11 3.6 0.6 -18.0 -3.6 Yes No Yes C12 4.0 0.3 -20.1 -3.0
No No No 11 2.1 0.4 -10.1 -2.7 Yes Yes Yes C13 4.0 0.4 -18.6 -3.5
No No No 12 13 1.8 0.2 -2.5 -3.3 Yes Yes Yes HRPET 0.1 0.3 -1.8
-0.4 No No No TPT 0.8 0.0 -1.3 -0.4 No No No
[0176] After 1000 hours of damp heat conditioning at 85.degree. C.
and 85% RH, it was found that looking through the front glass,
certain modules had yellowed. It was found the yellowness was due
to yellowing of the encapsulant and not the backsheet. As shown in
Table 17, small changes in the b color value were noted on the back
side (-3 b shift) but large changes in the b value were noted for
the front side on certain modules. It was also found that cracks
were appearing on selected backsheets in the modules treated with
periods of thermal cycling and freezing after high humidity
exposure.
[0177] Comparing the available MVTR data in Table 14, there is a
correlation between the observed yellowing of the encapsulant and
the MVTR. Lower MVTR corresponds to less yellowing. Cracking was
not observed for mini modules fabricated from sheets with
polyamide-ionomer formulations that contained talc.
[0178] Additional backsheets were prepared according to Table 18.
Blend K in Table 18 is a mixture of 85 weight % of a 65:35 blend of
high density polyethylene and ION-1 and 15 weight % of TiO.sub.2
and UV stabilizers available from Mosaic Color and Additives, 110
Sulphur Springs Road, Greenville, S.C. under the commercial
designation M002132WTPEP. The sheets were tested for MVTR at
85.degree. C. and 100% relative humidity as described in the
following procedure. MVTR was estimated by measuring the weight
loss of water filled, flanged aluminum cups lidded with the
backsheet in an 85.degree. C. air circulating oven. To minimize
bulging of the backsheet from the water vapor pressure at
85.degree. C., an 80 mesh stainless steel screen supported the
backsheet on the non-water side of the cup. Backsheet and mesh
screen were fixed in place by a retaining ring that bolted to the
flange of the aluminum cup. The weight loss (water loss) from the
cup was measured each day over the course of seven days. Typically
after 24 hours of conditioning at 85.degree. C., the daily mass
loss was consistent. The average daily mass loss was then corrected
for the surface area of the lidding backsheet to estimate the
transmission rate. Each backsheet was tested in duplicate and the
average of two measures reported. The nominal dimensions of the
inside of the flanged aluminum cups, was diameter 76 mm and the
depth 50 mm. The cups were typically half filled with water (150 ml
of water added to the cup).
TABLE-US-00020 TABLE 18 MVTR Outer skin layer Tie layer Core layer
Tie layer Inner skin layer (g/[m.sup.2-day]) 14 50 .mu.m Blend E --
250 .mu.m Blend 10 30 .mu.m Tie-2 50 .mu.m Blend K 56 15 50 .mu.m
Blend E -- 250 .mu.m Blend 12 30 .mu.m Tie-2 50 .mu.m Blend K 46 16
300 .mu.m Blend 13 -- -- 30 .mu.m Tie-2 50 .mu.m Blend K 44 C14 300
.mu.m Blend J -- -- 30 .mu.m Tie-2 50 .mu.m Blend K 49 17 300 .mu.m
Blend 13 -- -- 30 .mu.m Tie-1 50 .mu.m Blend K 57 C15 300 .mu.m
Blend J -- -- 30 .mu.m Tie-1 50 .mu.m Blend K 66 18 200-250 .mu.m
Blend I -- -- 25-50 .mu.m Tie-2 50-75 .mu.m Blend H 56 19 50-55
.mu.m Blend I 40-50 .mu.m Tie-3 150-200 .mu.m Blend I 40-50 .mu.m
Tie-3 50-55 .mu.m Blend I
* * * * *