U.S. patent application number 11/557135 was filed with the patent office on 2007-03-22 for solar panel including a low moisture vapor transmission rate adhesive composition.
Invention is credited to Louis Anthony Ferri, Steven Michael Milano.
Application Number | 20070062573 11/557135 |
Document ID | / |
Family ID | 31946290 |
Filed Date | 2007-03-22 |
United States Patent
Application |
20070062573 |
Kind Code |
A1 |
Ferri; Louis Anthony ; et
al. |
March 22, 2007 |
SOLAR PANEL INCLUDING A LOW MOISTURE VAPOR TRANSMISSION RATE
ADHESIVE COMPOSITION
Abstract
A solar panel including a front panel; a photovoltaic material
layer deposited either directly on the front panel or directly on
an anti-reflective coating formed between the front panel and the
photovoltaic material layer; a backing panel; and an adhesive layer
disposed between and adhering together the photovoltaic material
layer and the backing panel, in which the adhesive layer comprises
an adhesive composition, the adhesive composition comprising a low
MVTR polymer or copolymer and a silane-modified polymer or
copolymer. In another embodiment, the solar panel includes module
wire openings which are filled by an adhesive composition
comprising a low MVTR polymer or copolymer and a silane-modified
polymer or copolymer. A method of making the solar panel is
provided.
Inventors: |
Ferri; Louis Anthony;
(Solon, OH) ; Milano; Steven Michael; (Aurora,
OH) |
Correspondence
Address: |
Thomas W. Adams;Renner, Otto, Boisselle & Sklar, LLP
19th Floor
1621 Euclid Avenue
Cleveland
OH
44115
US
|
Family ID: |
31946290 |
Appl. No.: |
11/557135 |
Filed: |
November 7, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10224983 |
Aug 21, 2002 |
|
|
|
11557135 |
Nov 7, 2006 |
|
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Current U.S.
Class: |
136/251 |
Current CPC
Class: |
B32B 17/10036 20130101;
Y02E 10/50 20130101; H01L 31/02013 20130101; H01L 31/0481 20130101;
H01L 31/048 20130101; B32B 17/10174 20130101 |
Class at
Publication: |
136/251 |
International
Class: |
H02N 6/00 20060101
H02N006/00 |
Claims
1. A solar panel comprising: a front panel comprising glass; a
photovoltaic material layer deposited either directly on the front
panel or directly on an anti-reflective coating formed between the
front panel and the photovoltaic material layer; a backing panel;
and an adhesive layer adhering the photovoltaic material layer to
the backing panel, wherein the adhesive layer comprises an adhesive
composition, the adhesive composition comprising a low MVTR polymer
or copolymer and a silane-modified polymer or copolymer, wherein
the low MVTR polymer or copolymer is different from the
silane-modified polymer or copolymer.
2. The solar panel of claim 1, wherein the silane-modified polymer
or copolymer is crosslinked as a result of exposure to atmospheric
oxygen or moisture.
3. The solar panel of claim 1, wherein the adhesive composition has
a MVTR less than about 3 grams per square meter per day.
4. The solar panel of claim 1, wherein the low MVTR polymer or
copolymer comprises at least one of a polyisobutylene, an
isobutylene-isoprene copolymer, an
isobutylene-isoprene-divinylbenzene copolymer, a chlorinated or
brominated butyl rubber, an isobutylene-brominated p-methylstyrene
copolymer, an isobutylene-p-methylstyrene copolymer, a
chlorosulfonated polyethylene, an ethylene-alkyl (meth)acrylate
copolymer, an acrylonitrile-butadiene copolymer, polychloroprene,
or a mixture of two or more thereof.
5. The solar panel of claim 1, wherein the silane-modified polymer
or copolymer comprises a homopolymer of propylene, or a copolymer
of propylene and at least one C.sub.2-C.sub.8 .alpha.-olefin.
6. The solar panel of claim 1, wherein the silane-modified polymer
or copolymer comprises a copolymer of propylene and one or more of
maleic anhydride or an alkyl (meth)acrylate.
7. The solar panel of claim 1, wherein the low MVTR polymer or
copolymer is polyisobutylene and the silane-modified polymer is
silane-modified amorphous polypropylene.
8. The solar panel of claim 1, wherein the adhesive composition
further comprises a cross-linking initiator capable of initiating
cross-linking between silyl groups on the silane-modified polymer
or copolymer.
9. The solar panel of claim 1, wherein the silane-modified polymer
or copolymer comprises one or more of a silane-modified amorphous
.alpha.-olefin polymer or copolymer, a silane-crosslinkable
halogenated polymer composition, and a silane grafted copolymer of
a monoolefin and a vinyl aromatic monomer.
10. The solar panel of claim 1, wherein the silane-modified polymer
or copolymer is provided as a silane-modified amorphous
.alpha.-olefin polymer or copolymer comprising silyl groups having
a structure (I): --Si(OR.sup.1).sub.n(R.sup.2).sub.m (I) wherein
each of R.sup.1 and R.sup.2 independently is a C.sub.1-C.sub.8
branched or unbranched alkyl group, n=1 to 3, m=0 to 2, and m+n=3,
and the --Si is bonded directly to a carbon atom of the polymer or
copolymer.
11. The solar panel of claim 1, wherein the silane-modified polymer
or copolymer is provided as a silane-crosslinkable halogenated
polymer composition comprising the reaction product of a mixture of
100 parts by weight of a halogenated polymer and about 0.1 to about
20 parts by weight of an amino group-containing silane compound
having the following general structure (II): RHNR'Si(OR'').sub.3
(II) wherein R is hydrogen, an alkyl or a phenyl group, R' is an
alkylene group, OR'' is an alkoxy or alkoxyalkoxy group having 1 to
6 carbon atoms, wherein the N atom is bonded to a position on the
polymer replacing a halogen.
12. The solar panel of claim 1, wherein the silane-modified polymer
or copolymer is provided as a silane grafted copolymer comprising
the reaction product of at least 50 mole % of at least one
C.sub.3-C.sub.7 monoolefin and from about 0.1 up to 50 mole % of at
least one vinyl aromatic monomer, in which the silane has the
general structure (III): RR'SiY.sub.2 (III) wherein R represents a
monovalent olefinically unsaturated hydrocarbon or hydrocarbonoxy
radical reactive with the free radical sites produced on the
backbone polymer, Y represents a hydrolyzable organic radical and
R' represents an alkyl or aryl radical or a Y radical, wherein the
R radical becomes bonded to the polymer or copolymer.
13. The solar panel of claim 1, wherein the adhesive composition
further comprises an adhesion promoter comprising one or more of a
silane, a titanate, a zirconate or a zirco-aluminate.
14. The solar panel of claim 1, wherein the adhesive composition
further comprises a cross-linking catalyst.
15. The solar panel of claim 1, wherein the adhesive composition
further comprises a plasticizer.
16. The solar panel of claim 1, wherein the adhesive composition
further comprises a tackifying resin.
17. The solar panel of claim 1, wherein the solar panel comprises
module wire openings extending through at least one of the
photovoltaic material layer or the backing panel and a module wire
adhesive sealing the module wire openings, wherein the module wire
adhesive comprises a low MVTR polymer or copolymer and a
silane-modified polymer or copolymer, the module wire adhesive
having a different composition than the composition of the
adhesive.
18. The solar panel of claim 1 wherein the photovoltaic material
comprises a vapor deposited photovoltaic material.
19. The solar panel of claim 1 wherein the adhesive composition
extends to outer edges of the solar panel, is exposed to the
atmosphere at the outer edges, and the low MVTR polymer or
copolymer provides a barrier to moisture ingress at the outer
edges.
20. A method of fabricating a solar panel comprising a photovoltaic
material layer and a backing panel, the method comprising: (a)
providing a front panel suitable for use in a solar panel; (b)
vapor depositing a photovoltaic material layer on the front panel;
(c) forming an adhesive composition having a low moisture vapor
transmission rate by combining a low MVTR polymer or copolymer with
a silane-modified polymer or copolymer, wherein the low MVTR
polymer or copolymer is different from the silane-modified polymer
or copolymer; (d) adhering the photovoltaic material layer to the
backing panel using the adhesive composition; and (e) cross-linking
the silane-modified polymer or copolymer.
21. The method of claim 20, wherein step the adhesive composition
further comprises a cross-linking catalyst.
22. The method of claim 20, wherein upon cross-linking, the
silane-modified polymer or copolymer forms a network with the low
MVTR polymer or copolymer interpenetrating the network.
23. The method of claim 20, wherein the front panel comprises
glass.
24. The method of claim 20, wherein step (d) comprises applying a
layer of the adhesive composition to the photovoltaic material
layer.
25. The method of claim 20, wherein the solar panel comprises
module wire openings extending through at least one of the
photovoltaic material layer or the backing panel, and the method
further comprises applying the low MVTR adhesive composition to the
module wire openings.
26. The method of claim 20, wherein the cross-linking is initiated
by exposure of the adhesive composition to atmospheric oxygen or
moisture.
27. The method of claim 20, wherein the adhesive composition has a
MVTR less than about 3 grams per square meter per day.
28. The method of claim 20 wherein the vapor depositing is by one
or more of sputtering, physical vapor deposition, or chemical vapor
deposition.
29. The method of claim 20 wherein the adhesive composition is
applied to extend to outer edges of the solar panel, is exposed to
the atmosphere at the outer edges, and the low MVTR polymer or
copolymer provides a barrier to moisture ingress at the outer
edges.
30. A solar panel comprising: a front panel; a photovoltaic
material layer vapor deposited either directly on the front panel
or directly on an anti-reflective coating formed between the front
panel and the photovoltaic material layer; a backing panel; and an
adhesive layer adhering the photovoltaic material layer to the
backing panel, wherein the adhesive layer comprises an adhesive
composition, the adhesive composition comprising a low MVTR polymer
or copolymer and a silane-modified polymer or copolymer, wherein
the low MVTR polymer or copolymer is different from the
silane-modified polymer or copolymer.
31. The solar panel of claim 30 wherein the front panel comprises
glass.
32. The solar panel of claim 30 wherein the adhesive composition
extends to outer edges of the solar panel, is exposed to the
atmosphere at the outer edges, and the low MVTR polymer or
copolymer provides a barrier to moisture ingress at the outer
edges.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation of and claims
priority under 35 U.S.C. .sctn.120 to copending, commonly owned
U.S. application Ser. No. 10/224,983, filed 21 Aug. 2002, the
entirety of which is hereby incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to a solar panel including an
adhesive layer including an adhesive composition which has a low
moisture vapor transmission rate. The invention also relates to the
fabrication of solar panels using such compositions for adhesive
and for sealing around module wires and other structural elements
of solar panels.
BACKGROUND OF THE INVENTION
[0003] Photovoltaic solar panels, also referred to simply as solar
panels, are generally of two basic designs. One design employs
crystalline silicon wafers connected together and embedded in a
laminating film. The laminating film and the wafers embedded
therein are typically sandwiched between two lights, or panels, of
glass, a polymeric material or other suitable materials.
[0004] The second solar panel design, which is of primary interest
herein, employs one of amorphous silicon, cadmium-telluride
(Cd--Te) or copper-indium-diselenide, CuInSe.sub.2 (commonly
referred to as "CIS"), or a similar semiconductor material such as
mentioned below, which is deposited on a substrate in a thin film.
These thin film photovoltaic materials are typically deposited in a
thin film on a glass substrate by a method such as sputtering, PVD
or CVD. The individual photocells are typically formed by a laser
etching process, and are connected together by suitable circuitry,
such as a bus bar. The bus bar transfers to a storage device the
electrical current output from the photocells. The thin film
photovoltaic material and associated circuitry may be covered by a
sputtered layer of aluminum, which acts to protect the underlying
structures. To complete the construction, an assembly adhesive is
applied over the photovoltaic material, associated circuitry, and
any protective layer which is present, and a backing material is
applied. The backing material is typically glass, but may be metal,
a composite or a plastic material.
[0005] In addition to the above noted CIS, other combinations of
Group I, Group III and Group IV (referred to as I-III-IV)
semiconductor materials have been used and/or proposed for use as
photovoltaic materials. A number of different I-III-VI
semiconductor materials have been proposed for use in photovoltaic
cells. Some examples include AgInS.sub.2, AgGaSe.sub.2,
AgGaTe.sub.2, AgInSe.sub.2, AgInTe.sub.2, CuGaS.sub.2, CuInS.sub.2,
CuInTe.sub.2, CuAlS.sub.2, and CuGaSe.sub.2. Most attention,
however, has been focused on CIS and variations of CIS in which a
portion of the indium is replaced with one or more of aluminum and
gallium and/or a portion of the selenium is replaced with sulfur
and/or tellurium. Two promising variations of CIS that have been
proposed include CuIn.sub.xGa.sub.1-xSe.sub.2 (commonly referred to
as "CIGS") and CuIn.sub.xGa.sub.1-xSe.sub.yS.sub.2-y (commonly
referred to as "CIGSS"). These and other I-III-VI semiconductors
may be used in photovoltaic cells, as is known in the art.
[0006] The circuitry, such as a bus bar, which collects the
electrical current generated by the solar panel must be connected
by wiring to a suitable storage device, such as a battery. Such
wiring may be referred to as a "module wire" or "module lead". The
module wire must exit the solar panel at some point. Additional
adhesive or sealant material is needed to seal around the module
wire exiting the solar panel. The adhesive used for sealing around
module wires may be the same as, or may differ from, the assembly
adhesive used to attach the backing material to the solar
panel.
[0007] Solar panels are used outdoors, and so are exposed to the
elements, including wind, water and sunlight. Solar panels are
deleteriously affected primarily by moisture which may permeate
into the panel, reaching the electrical connections or the
photovoltaic materials. Water penetration into solar panels has
been a long-standing problem. Thus, various attempts have been made
to reduce the moisture vapor transmission rate (MVTR). Solar panels
may also be deleteriously affected by wind and sunlight, which may
result in failure of the adhesive layer. Wind causes obvious
physical damage, and sunlight results in heating of the solar panel
and exposure to ultraviolet (UV) radiation. Operating temperatures
of solar panels have been measured as high as 110.degree. C.
Thermoplastic adhesives soften at elevated temperatures and are
susceptible to UV-induced breakdown. Many thermosetting materials
suffer from unacceptably high MVTR.
[0008] One presently used assembly adhesive is ethylene vinyl
acetate (EVA). The EVA is applied to the solar panel together with
a peroxide which can crosslink the EVA. The EVA is then cured in
place on the solar panel by application of heat or radiation, which
causes the peroxide to crosslink the EVA. Crosslinked EVA provides
high strength, but suffers from a relatively high MVTR.
[0009] Module wire sealing materials suffer from the same problems
as do the assembly adhesives. Presently used module wire
adhesive/sealants include epoxy compounds and hot melt butyl
compounds. Epoxy compounds suffer from relatively high MVTR. The
hot melt butyl systems suffer from the inability to achieve high
strength since they are generally supplied as a thermoplastic
material and they lose strength as temperatures increase, as noted
above.
[0010] The problems of excluding moisture from solar panels, and of
finding adhesives with suitably low MVTR properties, in addition to
the other properties required of such adhesives, have been long
standing. Many attempts have been made to provide suitable adhesive
materials. However, none has satisfactorily provided both the
required strength and related properties, and the required low MVTR
properties. The present invention provides a solution to this
problem by providing a low MVTR adhesive material suitable for use
in a solar panel.
SUMMARY OF THE INVENTION
[0011] The present invention relates to an adhesive composition
suitable for use with solar panels which provides both a low MVTR
and strength and related properties.
[0012] In one embodiment, the present invention relates to a solar
panel including a photovoltaic material layer, a backing panel and
an adhesive layer adhering the photovoltaic material layer to the
backing panel, in which the adhesive layer comprises an adhesive
composition, the adhesive composition comprising a low MVTR polymer
or copolymer and a silane-modified polymer or copolymer. In one
embodiment, the adhesive layer has a MVTR less than about 3
g/m.sup.2/d.
[0013] In another embodiment, the present invention relates to a
solar panel including a photovoltaic material layer, a backing
panel, an adhesive layer adhering the photovoltaic material layer
to the backing panel, module wire openings extending through at
least one of the photovoltaic material layer or the backing panel,
and a module wire adhesive composition sealing the module wire
openings, the module wire adhesive composition including a low MVTR
polymer or copolymer and a silane-modified polymer or copolymer. In
one embodiment, the module wire sealant/adhesive composition has a
MVTR less than about 3 g/m.sup.2/d .
[0014] In one embodiment, the present invention relates to a method
of fabricating a solar panel comprising a photovoltaic material
layer and a backing panel, the method including steps of (a)
forming an adhesive composition having a low moisture vapor
transmission rate by combining a low MVTR polymer or copolymer with
a silane-modified polymer or copolymer; (b) adhering the
photovoltaic material layer to the backing panel using the adhesive
composition; and (c) cross-linking the silane-modified polymer or
copolymer. In one embodiment, the adhesive composition has a MVTR
less than about 3 g/m.sup.2/d.
[0015] The adhesive composition of the present invention provides
an advantage in that, in addition to having a low MVTR, due to the
presence of excess silane groups on the silane-modified polymer or
copolymer, any moisture which may find its way into the adhesive
composition merely results in further cross-linking of the
silane-modified polymer or copolymer, rather than resulting in any
break-down or deterioration of the adhesive composition or other
components of the solar panel. Thus, in addition to providing
enhanced strength and substrate adhesion to the adhesive
composition, the silane-modified polymer or copolymer provides
extended protection from any moisture which may penetrate into the
adhesive composition.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 is a schematic cross-sectional view of layers of a
solar panel, including a layer of the low MVTR adhesive material in
accordance with the present invention.
[0017] FIG. 2 is a schematic cross-sectional view of layers of a
solar panel, similar to FIG. 1, but also including a protective
layer, and a layer of the low MVTR adhesive material, in accordance
with the present invention.
[0018] FIG. 3 is a schematic plan view of a solar panel.
[0019] FIG. 4 is a schematic chemical structure of molecules of a
silane-modified polymer prior to crosslinking, in accordance with
one embodiment of the present invention.
[0020] FIG. 5 is a schematic chemical structure of molecules of a
silane-modified polymer subsequent to crosslinking, in accordance
with one embodiment of the present invention.
[0021] FIG. 6 is a schematic cross-sectional view of a solar panel
including a module wire opening in accordance with an embodiment of
the present invention.
[0022] FIG. 7 is a schematic cross-sectional view of the solar
panel of FIG. 6 including the module wire opening filled with a
module wire adhesive in accordance with an embodiment of the
present invention.
[0023] FIG. 8 is a flow diagram schematically illustrating the
steps of a method of fabricating a solar panel in accordance with
an embodiment of the present invention.
[0024] It should be appreciated that for simplicity and clarity of
illustration, elements shown in the figures have not necessarily
been drawn to scale. For example, the dimensions of some of the
elements are exaggerated relative to each other for clarity.
Further, where considered appropriate, reference numerals have been
repeated among the figures to indicate corresponding elements.
[0025] Furthermore, it should be appreciated that the process steps
and structures described below do not form a complete process flow
for manufacturing solar panels. The present invention can be
practiced in conjunction with solar panel fabrication techniques
currently used in the art, and only so much of the commonly
practiced process steps are included as are necessary for an
understanding of the present invention.
DETAILED DESCRIPTION
[0026] In one embodiment, the present invention relates to a solar
panel, in which the solar panel includes a photovoltaic material
layer and a backing panel, with an adhesive layer adhering the
photovoltaic material layer to the backing panel. In one
embodiment, the adhesive layer includes an adhesive composition
including a low moisture vapor transmission rate (MVTR) polymer or
copolymer and a silane-modified polymer or copolymer.
[0027] The solar panel may be of any type known in the art. The
solar panel thus includes a photovoltaic material layer, for
generating an electrical current from sunlight impinging upon the
solar panel. In one embodiment, the photovoltaic material layer
includes a layer of amorphous silicon, cadmium telluride,
copper-indium-diselenide (CIS), or another Group I-III-IV
semiconductor material, such as those discussed above.
[0028] In another embodiment, the solar panel comprises crystalline
silicon wafers connected together and embedded in a laminating
film. The crystalline silicon may be polycrystalline or
monocrystalline silicon. The present invention is applicable to
both of these types of solar panels. In addition, the present
invention is applicable to solar panels including other
photovoltaic materials, such as gallium arsenide on germanium
(GaAs/Ge(i)), gallium arsenide on gallium arsenide (GaAs/GaAs), or
gallium indium phosphide on gallium arsenide/germanium
(GaInP/GaAs/Ge). The photovoltaic material layers including
amorphous silicon, cadmium telluride or copper-indium-sulfide are
more susceptible to intrusion of moisture than are the panels
including crystalline silicon, so potentially benefit more from the
present invention. The present invention is not limited to any
particular type of solar panel. Accordingly, for exemplary but
non-limiting purposes, photovoltaic material layers including
amorphous silicon, cadmium telluride or copper-indium-sulfide, and
in particular, amorphous silicon, are described herein.
[0029] The photovoltaic material layer is formed on a front panel
of material which may be, for example, ordinary borosilicate glass.
In another embodiment, the front panel is low-iron glass, which
allows more sunlight to pass through the glass. In addition to
glass, the front panel (and the backing panel) may be formed of a
tough plastic film, such as TEDLAR.RTM. brand of polyvinylfluoride
(PVF) (a product of E. I. du Pont De Nemours and Co.). PVF, such as
TEDLAR.RTM. PVF, has a high coefficient of visible light
transmission and low coefficient of infrared light transmission so
that heat is not transmitted back through the front panel. The
front panel should be a material which is not harmed by ultraviolet
light since it will be continuously exposed to ultraviolet
radiation during daylight hours. Other light transmissive, UV
resistant polymers may be used, such as copolymers such as ethylene
tetrafluoride-perfluorovinyl ether copolymers (PFA), commercially
available as NEOFLON.RTM. PFA film from Daikin Industry K.K.,
ethylene tetrafluoride-propylene hexafluoride copolymers (FEP)
commercially available as FEP type Toyoflon film from Toray K.K.,
and ethylene tetrafluoride-ethylene copolymers (ETFE) commercially
available as TEFZEL.RTM. ETFE film from E. I. du Pont. In one
embodiment, the front panel is glass and the back panel is a
material such as TEDLAR.RTM. PVF, or another of the polymeric
materials. Other suitable materials may be used as the front panel
and the backing panel, as known in the art.
[0030] The front panel and the photovoltaic material layer are
adhered to a backing panel. The backing panel provides additional
strength to the solar panel and provides protection to the
photovoltaic material layer. The adhesive used to adhere the
backing panel to the photovoltaic material layer is an important
component of the solar panel, as described in more detail
below.
[0031] As known in the art, other layers may be included, such as,
for example, an anti-reflective coating formed between the front
panel and the photovoltaic material layer, to prevent reflection of
incoming sunlight out of the solar panel. As known in the art, the
photovoltaic material layer may comprise juxtaposed layers of n-
and p-doped semiconductor materials which actually generate the
electricity from the incoming sunlight.
[0032] One embodiment of a typical solar panel 100 in accordance
with the present invention is shown in a cross-sectional schematic
view in FIG. 1. The solar panel 100 includes a photovoltaic
material layer 102. A first surface 102a of the photovoltaic
material layer 102 is disposed on and attached to a front panel
104. On a second surface 102b of the photovoltaic material layer
102 is disposed an adhesive composition layer 106, including a low
MVTR adhesive. The adhesive layer 106 forms a bond between the
photovoltaic material layer 102 and a backing panel 108.
[0033] Another embodiment of a typical solar panel 200 in
accordance with the invention is shown in a cross-sectional
schematic view in FIG. 2. The solar panel 200 of FIG. 2 includes
substantially the same elements of the panel 100 shown in FIG. 1,
and further includes a protective layer 110 disposed between the
photovoltaic material 102 and the adhesive layer 106. The
protective layer may be a metal such as aluminum, which is
deposited over the photovoltaic layer 102. The protective material
may also be any other material known in the art for this purpose,
such as aluminum, copper, gold, silver, alloys of these materials,
or another suitably protective metal. In one embodiment, the
protective layer 110 is also employed as a current carrier. In such
an embodiment, the material of which the protective layer 110 is
formed should be conductive, as well as having sufficient strength
to provide the desired protection.
[0034] A typical solar panel, such as the panel 100, may be
fabricated by depositing the photovoltaic material layer 102, e.g.,
amorphous silicon, on the front panel 104. As noted, the front
panel 104 may be formed of any appropriate material, and in many
instances the material is glass. The photovoltaic material layer
102 may be deposited by any appropriate means known in the art. For
example, amorphous silicon may be deposited by chemical vapor
deposition (CVD), by physical vapor deposition (PVD), by sputtering
or by any other known method. The CVD methods may include any of a
variety of methods, for example, CVD, PECVD, RTCVD, ALCVD, MOCVD or
LPCVD.
[0035] FIG. 3 is a plan view of the front panel 104 of a solar
panel 300, in accordance with another embodiment of the present
invention. The outer border of the front panel 104 is shown in
broken lines to indicate that the panel extends beyond the small
portion shown in FIG. 3. When the photovoltaic material layer 102
has been deposited on the front panel 104, the photovoltaic layer
102 is etched to define a plurality of individual photocells 112,
as shown in FIG. 3. Thus, the plurality of individual photocells
112 shown in plan view in FIG. 3 are substantially the same as the
layer 102 shown in cross-sectional view in FIG. 2. The etching may
be by application of a laser etching, or by other suitable means,
including chemical etching and other etching methods known in the
semiconductor arts.
[0036] As shown in FIG. 3, the individual photocells 112 must be
electrically connected so that the electrical current generated by
the photocells can be collected and carried to a location at which
the electrical current can be used. Thus, an electrical connection,
such as a bus bar or other suitable wiring, is applied to the solar
panel 300 to provide an electrical connection between respective
ones of the plurality of individual photocells 112 and the exterior
of the solar panel 300. The wiring is connected from one photocell
112 to another as known in the art. FIG. 3 shows two embodiments of
such wiring. First, in the upper row of photocells 112 in FIG. 3,
there is schematically shown a series of photocell to photocell
wiring connections 114. As shown, this series of wiring connections
114 connects from one side a first photocell 112 to the opposite
side of an adjacent photocell 112, or to the exterior of the solar
panel 300. This side to side connection is indicated by the dashed
and solid lines at the point of attachment of the wiring connection
114 to each respective photocell 112. The second embodiment of
electrical connection is shown in the lower row of photocells 112,
which schematically shows a bus bar 116. The bus bar 116 provides
an electrical connection from photocell to photocell and to the
exterior of the solar panel 300.
[0037] If a protective layer, such as the layer 110 is used, it
typically is deposited on the etched, "wired-in" photovoltaic layer
102, which usually is formed on the front panel 104. The protective
layer 110 may be deposited by any means which is known in the art
for depositing the particular material used, and which is
compatible with the material of which the photovoltaic material
layer is made. Thus, for example, the protective layer 110, if a
metal, may be deposited by an appropriate CVD method, such as one
of those noted above, or by PVD or by sputtering. If the protective
material layer 110 is a polymeric material, it may be deposited by
a lamination procedure, by direct polymerization on the
photovoltaic layer 102, by application of a solvent-free (neat) or
solubilized prepolymer, followed by a polymerization thereof, or by
any other means known in the art. Other known protective materials
may be used, and these may be deposited on the photovoltaic layer
102 by appropriate means.
[0038] The adhesive layer 106 may be applied to be in direct
contact with the photovoltaic material layer 102 in an embodiment
such as shown in FIG. 1. In an embodiment having a protective layer
110, such as shown in FIG. 2, the adhesive layer 106 may be applied
in contact with the protective layer 110. In both embodiments, the
adhesive layer is also in contact with the backing panel 108. Of
course, the adhesive may be initially applied to either the backing
panel 108 or to the photovoltaic material layer 102 or the
protective layer 110, and then subsequently applied to the opposite
layer when the panels are brought into sealing contact. Thus, the
adhesive layer 106 is disposed between and adheres together the
photovoltaic material layer 102 and the backing panel 104, with the
protective layer 110 intervening between these layers in some
embodiments.
[0039] The adhesive layer 106 is often referred to as an assembly
adhesive, since it is used to assemble and hold together the
elements of the solar panel. In the present invention, the adhesive
layer 106 includes an adhesive composition having a low moisture
vapor transmission rate (MVTR). In accordance with one embodiment
of the present invention, the adhesive composition includes a low
MVTR polymer or copolymer and a silane-modified polymer or
copolymer.
[0040] In one embodiment, the low MVTR polymer or copolymer
includes at least one of a polyisobutylene, an isobutylene-isoprene
copolymer, an isobutylene-isoprene-divinylbenzene copolymer, a
chlorinated or brominated butyl rubber, an isobutylene-brominated
p-methylstyrene copolymer, an isobutylene-p-methylstyrene
copolymer, a chlorosulfonated polyethylene, an ethylene-alkyl
(meth)acrylate copolymer, an acrylonitrile-butadiene copolymer, a
polychloroprene, an epichlorohydrin rubber, or mixtures of two or
more thereof. In one embodiment, the low MVTR polymer or copolymer
is other than polychloroprene, which in some forms may not provide
a satisfactory MVTR.
[0041] In one embodiment, the low MVTR polymer or copolymer is
polyisobutylene. In one embodiment, the polyisobutylene has a
number-average molecular weight in the range from about 20,000 to
about 2,000,000. In another embodiment, the polyisobutylene has a
number-average molecular weight in the range from about 50,000 to
about 500,000. In another embodiment, the polyisobutylene has a
number-average molecular weight in the range from about 75,000 to
about 300,000.
[0042] In one embodiment, the low MVTR polymer or copolymer is a
copolymer including monomeric units of isobutylene and another
monomer such as isoprene, 1,3-butadiene, p-methylstyrene or other
styrene derivatives.
[0043] Here and throughout the specification and claims, the limits
of the disclosed ranges and ratios may be combined.
[0044] In one embodiment, the silane-modified polymer or copolymer
includes one or more of a silane-modified amorphous .alpha.-olefin
polymer or copolymer, a silane-crosslinkable halogenated polymer
composition, and a silane grafted copolymer of a monoolefin and a
vinyl aromatic monomer.
[0045] In one embodiment, the silane-modified amorphous
.alpha.-olefin polymer or copolymer includes monomeric units of
propylene. In another embodiment, the silane-modified amorphous
.alpha.-olefin polymer or copolymer includes a homopolymer of
propylene, or a copolymer of propylene and at least one
C.sub.2-C.sub.8 .alpha.-olefin. In another embodiment, the
silane-modified amorphous .alpha.-olefin polymer or copolymer
includes a copolymer of propylene and one or more of maleic
anhydride or an alkyl (meth)acrylate.
[0046] In one embodiment, the silane-modified amorphous
.alpha.-olefin polymer or copolymer comprises silyl groups having a
structure (I): --Si(OR.sup.1).sub.n(R.sup.2).sub.m (I) wherein each
R.sup.1 independently is a C.sub.1-C.sub.8 branched or unbranched
alkyl group, each R.sup.2 independently is either R.sup.1 or a
C.sub.1-C.sub.8 branched or unbranched alkyl group, n=1 to 3, m=0
to 2, and m+n=3. Thus, for example, the silyl group may be
trimethoxysilyl, triethoxysilyl, or methyldimethoxysilyl. As
indicated by the formula, the silyl group may have from one to
three OR.sup.1 substituents, and may have from zero to two alkyl
substituents.
[0047] In one embodiment, the adhesive composition includes
polyisobutylene as the low MVTR polymer or copolymer and
silane-modified amorphous polypropylene as the silane-modified
polymer or copolymer.
[0048] In one embodiment, the silane-modified polymer or copolymer
is a silane-crosslinkable halogenated polymer composition. In one
embodiment, the silane-crosslinkable halogenated polymer
composition contains a mixture of 100 parts by weight of a
halogenated polymer and about 0.1 to about 20 parts by weight of an
amino group-containing silane compound. In one embodiment, the
composition may be crosslinked in the presence of a silanol
catalyst. In one embodiment, the halogenated polymer is one or more
of polychloroprene (e.g., Neoprene.RTM.), chlorosulfonated
polyethylene, epichlorohydrin rubber and halogenated butyl rubber.
In one embodiment, the amino group-containing organic silane
compound has the following general structure (II):
RHNR'Si(OR'').sub.3 (II) wherein R is hydrogen, an alkyl or a
phenyl group, R' is an alkylene group, OR'' is an alkoxy or
alkoxyalkoxy group having 1 to 6 carbon atoms. In one embodiment,
the aminosilane compound is one or more of
N-phenylaminopropyltrimethoxysilane,
N-phenylaminopropyltriethoxysilane,
N-methylaminopropyltrimethoxysilane,
N-ethylaminopropyltriethoxysilane,
.gamma.-aminopropyltriethoxysilane or
.gamma.-aminopropyltrimethoxysilane.
[0049] In one embodiment, the adhesive composition includes
polyisobutylene as the low MVTR polymer or copolymer and
N-phenylaminopropyltrimethoxysilane modified polychloroprene as the
silane-modified polymer or copolymer.
[0050] In one embodiment, the silane-modified polymer or copolymer
is a silane grafted copolymer of a monoolefin and a vinyl aromatic
monomer. In one embodiment, suitable silane grafted copolymer of a
monoolefin and a vinyl aromatic monomer comprises copolymers
containing at least 50 mole % of at least one C.sub.3-C.sub.7
monoolefin and from about 0.1 up to 50 mole % of at least one vinyl
aromatic monomer. In one embodiment, the vinyl aromatic monomers
may be a mono-vinyl aromatic such as styrene, alpha-methylstyrene,
alkyl-substituted styrenes such as t-butylstyrene and para-alkyl
substituted styrenes wherein the alkyl group contains from 1 to 4
carbon atoms. In one embodiment, the vinyl aromatic compound is
p-methylstyrene. Suitable monoolefin monomers include propylene,
isobutylene, 2-butene and the like. In one embodiment,
substantially 100% of the monoolefinic content of the copolymer
comprises isobutylene. In one embodiment, the copolymer comprises
isobutylene and para-methylstyrene and contains from about 0.1 to
20 mole. % of p-methylstyrene.
[0051] In one embodiment, the organic silanes which are reacted
with the olefin copolymer to form the silane-grafted copolymer have
the general structure (III): RR'SiY.sub.2 (III) wherein R
represents a monovalent olefinically unsaturated hydrocarbon or
hydrocarbonoxy radical reactive with the free radical sites
produced on the backbone polymer, Y represents a hydrolyzable
organic radical and R' represents an alkyl or aryl radical or a Y
radical. Where R is a hydrocarbonoxy radical, it should be
non-hydrolyzable. In one embodiment, R may be a vinyl, allyl,
butenyl, 4-pentenyl, 5-hexenyl, cyclohexenyl or cyclopentadienyl
radical. In one embodiment, R is vinyl. In one embodiment, the
group Y may be one or a mixture of C.sub.1 to C.sub.4 alkoxy
radical such as methoxy, ethoxy or butoxy. In another embodiment, Y
is an acyloxy radical, such as formyloxy, acetoxy or propionoxy; or
an oximo radical such as --ON.dbd.C(CH.sub.3).sub.2,
--ON.dbd.C(CH.sub.3)(C.sub.2H.sub.5) and
--ON.dbd.C(C.sub.6H.sub.5).sub.2; or a substituted amino radical
such as alkylamino or arylamino radicals, including --NHCH.sub.3,
--NHC.sub.2H.sub.5 and --NHC.sub.6H.sub.5 radicals. In one
embodiment, R' represents an alkyl group, an aryl group or a Y
group. In one embodiment, the group R' can be exemplified by a
methyl, ethyl, propyl, butyl, phenyl, alkylphenyl group or a Y
group. In one embodiment, R' is a methyl or alkoxy group. In one
embodiment, the silanes are those where R' and Y are selected from
methyl and alkoxy groups, e.g., vinyltriethoxysilane,
vinyltrimethoxysilane and methyl vinyldimethoxysilane.
[0052] In one embodiment, the adhesive composition includes
polyisobutylene as the low MVTR polymer or copolymer and a
vinyltrimethoxysilane-modified copolymer of isobutylene and
para-methylstyrene as the silane-modified polymer or copolymer.
[0053] In one embodiment, the silane-modified polymer or copolymer
is crosslinked after the adhesive has been applied during the
fabrication of the solar panel. In one embodiment, the crosslinking
occurs as a result of exposure to atmospheric oxygen or moisture.
In this crosslinking reaction, first the alkoxy silyl groups are
hydrolyzed to form silanol or hydroxy-silyl compounds, and the
hydroxy-silyl groups react with other alkoxy silyl or hydroxy-silyl
groups to form cross links including Si--O--Si bonds. The silyl
groups may also react with other active hydrogens in the adhesive
composition or on the surface of glass panels to which the adhesive
attaches. The crosslinking forms a polymer network, through which
the low MVTR polymer interpenetrates. Thus, the combined polymers
of the adhesive composition create a high strength adhesive which
holds the components of the solar panel together, to provide a long
service life, and the presence of the low MVTR polymer or copolymer
substantially reduces moisture penetration.
[0054] The crosslinking reaction transforms the adhesive
composition from a thermoplastic-like material, which may be
applied as a hot melt or in a low-viscosity state, to a material
which is more like a thermosetting polymer. The initial,
thermoplastic form of the adhesive composition, prior to
crosslinking, has a specific melt flow index range. The melt flow
index can be measured, for example, by a method such as ASTM
D-1238-A or -B. The crosslinked adhesive composition may not have a
measurable melt flow index, since the crosslinking may prevent the
adhesive composition from flowing.
[0055] In one embodiment, the adhesive composition further includes
a crosslinking catalyst. In one embodiment, the crosslinking
catalyst may be an organotin compound or a titanate compound. In
one embodiment, the crosslinking catalyst includes one or more of
dibutyl tin dilaurate, tin oxide, dibutyl tin diacetate, dibutyl
tin oxide and a titanate. The crosslinking catalyst promotes the
reaction with water to initiate further crosslinking.
[0056] In one embodiment, upon crosslinking, the silane-modified
polymer or copolymer forms a network with the low MVTR polymer or
copolymer interpenetrating therethrough.
[0057] In one embodiment, the adhesive composition further includes
a crosslinking initiator capable of initiating crosslinking between
silyl groups on the silane-modified polymer or copolymer. In
general, however, the crosslinking initiator used in the present
invention is water. In one embodiment, the water which initiates
the crosslinking reaction is atmospheric moisture. As noted above,
atmospheric moisture which finds its way into the adhesive
composition subsequent to fabrication of the solar panel of the
present invention may initiate further crosslinking and/or may
react with residual silyl groups present in the adhesive
composition.
[0058] FIG. 4 is a schematic chemical structure of molecules of a
silane-modified polymer or copolymer prior to crosslinking, in
accordance with one embodiment of the present invention. As shown
in FIG. 4, the polymeric chain includes silyl groups attached at
various positions on the chain. In the embodiment shown in FIG. 4,
the silyl groups are tri-alkoxy (--OR) substituted silyl groups. In
one embodiment, the R group of the silyl groups shown in FIG. 4 may
be any of the R.sup.1 groups defined above. In another embodiment,
not shown, the silyl group may be any of the silyl groups defined
above in structure (I), e.g., silyl groups having the structure
--Si(OR.sup.1).sub.n(R.sup.2).sub.m, wherein R.sup.1, R.sup.2, n
and m have the meanings set forth above with respect to structure
(I).
[0059] FIG. 5 is a schematic chemical structure of molecules of the
silane-modified polymer or copolymer such as that of FIG. 4
subsequent to crosslinking, in accordance with one embodiment of
the present invention. As shown in FIG. 5, the silyl groups have
reacted with each other, and with --OH groups on the surface of a
substrate (such as the glass backing layer 108, or the photocell
substrate 102). Although not shown in FIG. 5, the remaining
--OR.sup.1 groups may either remain unreacted or may have reacted
with adjacent layers of the silane-modified polymer or copolymer,
i.e., into or above the plane of the paper in which the drawing is
shown, as suggested by the "empty" bonds extending laterally from
the Si atoms.
[0060] Although not shown, the other silane-modified polymers or
copolymers disclosed herein would form structures analogous to
those shown in FIGS. 4 and 5, with appropriate substitution of the
polymer backbone and reactive moieties, as defined with respect to
structures (II) and (III) above.
[0061] Although not shown in FIGS. 4 and 5, in the adhesive layer
of the present invention, the low MVTR polymer or copolymer would
be in the spaces between the silane-modified polymer or copolymer
molecules in both FIG. 4 and FIG. 5 (and in the analogous
structures from other silane-modified polymers or copolymers).
Thus, as described above, in one embodiment, the adhesive layer
includes the silane-modified polymer or copolymer and the low MVTR
polymer or copolymer, which together form an interpenetrating
network. In one embodiment, the adhesive layer includes the
crosslinked silane-modified polymer or copolymer, which forms a
network, and the low MVTR polymer or copolymer, which
interpenetrates through the network formed by the crosslinked
silane-modified polymer or copolymer. The adhesives of the present
invention including, in one embodiment, the crosslinked
silane-modified polymer or copolymer, and the low MVTR polymer or
copolymer, are high strength low MVTR adhesives which both hold
together the elements of the solar panel and provide a significant
barrier to moisture.
[0062] Moisture Vapor Transmission Rate (MVTR) is measured
according to ASTM Test Method F 1249-90. In carrying out this ASTM
method, the sample is prepared as follows. An adhesive film is
pressed into a mold, heated and pressed under vacuum to a thickness
from 0.050 to 0.060 inch (1.27 to 1.52 mm). The vacuum is used
during the heating and pressing operation to insure that the film
is created without air voids or bubbles. After the film is removed
from the press cavity it may be cured via exposure to moisture in a
high humidity environment. It is not necessary to cure the film
prior to testing for MVTR, as the MVTR value for a cured film or an
uncured film is nearly the same, since MVTR of elastomeric
adhesives is believed to be more related to the backbone of the
polymers in the film than to the crosslink density of the polymer.
In order to facilitate the ease of handling of the laminating
adhesive film, a five square centimeter die-cut aluminum mask is
used to hold the film. The mask, available from the equipment
manufacturer MOKON, Buffalo, N.Y., is designed to hold the film in
the test chamber. The die-cut aluminum mask has a five square
centimeter (5 cm.sup.2) opening cut into it that allows the testing
to proceed. A sample of the low MVTR adhesive composition film is
placed onto a die-cut aluminum mask. A second die-cut aluminum mask
is placed over the first with the adhesive composition film in
between. This now rigid structure can easily be placed into the
testing chamber and the MVTR tested on the 5 cm.sup.2 sample
exposed in the mask, according to the ASTM method.
[0063] As used herein, the term "low MVTR" or "low moisture vapor
transmission rate" means that the rate at which water vapor or
moisture is transmitted through the material to which this term is
applied, as measured by ASTM F 1249-90, is less than 5 grams per
square meter per day (g/m.sup.2/d). This rate of moisture vapor
transmission is generally regarded as "low".
[0064] In one embodiment, the adhesive composition has a moisture
vapor transmission rate (MVTR) less than about 3 g/m.sup.2/d. In
one embodiment, the adhesive composition has a MVTR less than about
1 g/m.sup.2/d. While ideally the minimum MVTR of the adhesive
composition would be zero, in one embodiment, the lowest MVTR is
about 0.05 g/m.sup.2/d for a low MVTR polymer such as PIB. Thus, in
one embodiment, the MVTR of the adhesive composition of the present
invention is in a range from about 0.075 to about 5 g/m.sup.2/d. In
another embodiment, the MVTR of the adhesive composition of the
present invention is in a range from about 0.1 to about 3
g/m.sup.2/d. In another embodiment, the MVTR of the adhesive
composition of the present invention is in a range from about 0.5
to about 2 g/m.sup.2/d.
[0065] In one embodiment, the adhesive composition further includes
a filler. In one embodiment, the filler includes calcium carbonate,
talc, barium sulfate, clay, silica, carbon black, titanium dioxide,
and a mixture of two or more thereof.
[0066] Since the adhesive composition should be non-conductive,
i.e., a dielectric material, the filler materials used should
either be non-conductive or if possibly conductive, should be used
at a level which does not result in the adhesive composition having
a dielectric strength of less than about 1.times.10.sup.8 ohmcm, as
determined by ASTM D 257. A typical, desirable dielectric strength
for the adhesive material is about 1.times.10.sup.9 ohmcm, as
determined by ASTM D 257.
[0067] In one embodiment, the adhesive composition further includes
an adhesion promoter. In one embodiment, the adhesion promoter
includes one or more of a silane, a titanate, a zirconate and a
zirco-aluminate.
[0068] In one embodiment, the silane adhesion promoting compounds
include vinyl silanes, amine-substituted alkyl or alkyl/alkoxy
silanes, and other known adhesion promoting silane compounds. In
one embodiment, the silane adhesion promoting compounds include
silanes having a general structure (IV):
Si(OR.sup.1).sub.n(R.sup.2).sub.m (IV) wherein each R.sup.1
independently is a C.sub.1-C.sub.8 branched or unbranched alkyl
group, each R.sup.2 independently is either R.sup.1 or a
C.sub.1-C.sub.8 branched or unbranched, substituted or
unsubstituted alkyl group or halogen, n=1 to 3, m=1 to 3, and
m+n=4. The substitution of the alkyl group may comprise, for
example, primary or secondary amines and the halogens. Thus, for
example, the silyl group may be trimethoxysilyl, triethoxysilyl,
methyldimethoxysilyl, trimethoxychlorosilane,
.gamma.-aminopropyltrimethoxysilane or
.gamma.-chlorobutyltriethoxysilane. As indicated by the formula,
the silyl group may have from one to three OR.sup.1 substituents,
and may have from one to three R.sup.2 substituents.
[0069] In one embodiment, the titanate and zirconate adhesion
promoting compounds typically have large (e.g., about 5 to about 20
carbon atoms) hydrocarbon or substantially hydrocarbon groups
attached to a central titanium or zirconium atom. Thus, in one
embodiment, these titanate and zirconate adhesion promoting
compounds contain from about 5 to about 100 carbon atoms, and in
one embodiment from about 20 to about 60 carbon atoms.
"Substantially hydrocarbon" describes groups which contain
heteroatom substituents which do not alter the predominantly
hydrocarbon nature of the group. The heteroatom substituents
containing non-hydrocarbon groups which, in the context of this
invention, do not alter the predominantly hydrocarbon nature of the
substituent, include groups such as chloro and fluoro; those
skilled in the art will be aware of such groups. In general, no
more than about 2, and in one embodiment, no more than one,
heteroatom substituents are present for every ten carbon atoms in
the hydrocarbon group. Typically, there are no such heteroatom
substituents in the hydrocarbon group.
[0070] Suitable zirco-aluminate adhesion promoting compounds are
commercially available from Rhone-Poulenc. Preparation of
aluminum-zirconium complexes is described in the U.S. Pat. Nos.
4,539,048 and 4,539,049. These patents describe zirco-aluminate
complex reaction products corresponding to the empirical formula
(V):
(Al.sub.2(OR.sub.1O).sub.aA.sub.bB.sub.c).sub.X(OC(R.sub.2)O).sub.Y(ZrA.s-
ub.dB.sub.e).sub.Z (V) wherein X, Y, and Z are at least 1, R.sub.2
is an alkyl, alkenyl, aminoalkyl, carboxyalkyl, mercaptoalkyl, or
epoxyalkyl group, having from 2 to 17 carbon atoms, and the ratio
of X:Z is from about 2:1 to about 5:1. Additional zirco-aluminate
complexes are described in U.S. Pat. No. 4,650,526. The disclosure
of these three patents relating to zirco-aluminate adhesion
promoting compounds is incorporated herein by reference.
[0071] In one embodiment, the adhesive composition further includes
a plasticizer. In one embodiment, the plasticizer includes one or
more of a hydrocarbon oil, an ester derivative of a dibasic acid, a
mineral oil, a paraffin, a paraffin derivative and a
polybutene.
[0072] In one embodiment, the adhesive composition further includes
a tackifying resin. In one embodiment, the tackifying resin
includes one or more of a rosin ester, a polyterpene, a polyterpene
derivative, a C.sub.5 hydrocarbon resin, a C.sub.9 hydrocarbon
resin, a phenolic resin and a natural resin.
[0073] In one embodiment, the solar panel further includes module
wire openings and a module wire adhesive composition sealing the
module wire openings. In one embodiment, the module wire adhesive
composition includes a low MVTR polymer or copolymer and a
silane-modified polymer or copolymer, but has a different
formulation than that in the adhesive layer disposed between and
adhering together the photovoltaic material layer and the backing
panel.
[0074] Thus, in one embodiment, the present invention further
relates to a solar panel including a photovoltaic material layer; a
backing panel; module wire openings in at least one of the
photovoltaic material layer or the backing panel; and a module wire
sealant/adhesive composition sealing the module wire openings, the
module wire sealant/adhesive composition, the sealant/adhesive
composition comprising a low MVTR polymer or copolymer and a
silane-modified polymer or copolymer. In one embodiment, the module
wire adhesive is the same adhesive as that used for the assembly
adhesive. In another embodiment, the module wire adhesive has a
different formulation from that of the assembly adhesive.
[0075] FIG. 6 is a schematic cross-sectional view of a solar panel
including a further embodiment of the present invention. FIG. 6
shows a solar panel 400 which includes the same elements described
above with respect to FIGS. 1-3, and further includes a module wire
118 and a module wire opening 120. As shown in FIG. 6, in one
embodiment, the module wire opening 120 extends through the backing
layer 108, to form a passageway through which the module wire 118
extends outside of the solar panel 400. The module wire 118 thus
provides an electrical connection from the plurality of individual
photocell elements 112, which generate the electrical current, to
the outside, where the electrical current is used.
[0076] FIG. 7 is a schematic cross-sectional view of a solar panel
400 such as that shown in FIG. 6, which further includes a module
wire adhesive 122 sealing the module wire 118 and the module wire
opening 120. In one embodiment, the module wire adhesive 122 is a
low MVTR adhesive in accordance with the present invention. In one
embodiment, the module wire adhesive 122 is the same adhesive as
that described above for use as the assembly adhesive 106. In one
embodiment, the module wire adhesive 122 comprises a greater
proportion level of the low MVTR polymer or copolymer component,
relative to the proportion of the silane-modified polymer or
copolymer. Since the module wire adhesive does not need the high
strength needed by the assembly adhesive, it is possible to
increase the loading of the MVTR polymer or copolymer component in
the adhesive composition relative to the silane-modified polymer or
copolymer component. This modification is of benefit in further
reducing the absolute amount of moisture which successfully enters
the solar panel due to the increase in loading of the MVTR polymer
or copolymer. This modification is also of benefit since the
reduced amount of silane-modified polymer or copolymer allows the
module wire adhesive 122 to be softer and therefore more compliant
to the possible movements of the module wire 118 without the danger
of creating a direct passageway through which moisture may enter
the interior of the solar panel.
[0077] In some embodiments (not shown), a frame, such as an
aluminum frame, may be formed around the solar panel. Such a frame
provides stability and locations at which mounting may be made. The
frame may be sealed to the solar panel by an appropriate adhesive.
In one embodiment, the frame is sealed to the solar panel by a low
MVTR adhesive composition, such as that of the present invention.
In one such embodiment, the low MVTR adhesive composition used to
adhere the frame to the solar panel is the assembly adhesive
described above. In another embodiment, the low MVTR adhesive
composition used to adhere the frame to the solar panel is the
module wire adhesive described above. In both embodiments in which
the frame is adhered to the solar panel with the low MVTR adhesive
composition, additional protection from moisture vapor penetration
is provided to the solar panel by the adhesive and the frame.
[0078] In other embodiments, the frame is sealed to the solar panel
by an adhesive such as a butyl hot melt adhesive, as is known in
the art and commonly used for this purpose. In addition, in some
embodiments, a butyl hot melt adhesive may be used as the module
adhesive for sealing around the module wires.
Method of Fabricating a Solar Panel
[0079] In one embodiment, the present invention relates to method
of fabricating a solar panel comprising a photovoltaic material
layer and a backing panel, the method including steps of (a)
forming an adhesive composition having a low moisture vapor
transmission rate by combining a low MVTR polymer or copolymer with
a silane-modified polymer or copolymer, (b) adhering the
photovoltaic material layer to the backing panel using the adhesive
composition, and (c) cross-linking the silane-modified polymer or
copolymer. In one embodiment, upon crosslinking, the
silane-modified polymer or copolymer forms a network with the low
MVTR polymer or copolymer interpenetrating therethrough.
[0080] In one embodiment, step (b) includes applying a layer of the
adhesive composition over the photovoltaic materials.
[0081] In one embodiment, the solar panel comprises module wire
openings, and the method further includes applying the adhesive
composition to the module wire openings.
[0082] FIG. 8 is a flow diagram schematically illustrating the
steps of a method of fabricating a solar panel in accordance with
the present invention. As shown in FIG. 8, in the first step of the
method, shown as step S801, a photovoltaic layer is provided. In
the usual case, the photovoltaic layer will have been deposited by
an appropriate process to one surface of a front panel, such as
that described above.
[0083] In addition, the photovoltaic layer usually will have been
separated into individual photovoltaic cells, or photocells. Each
of the photocells will have been electrically connected, as
appropriate to the design of the solar cell. Such matters may be
appropriately designed or selected by those of skill in the art,
and the present invention is not limited to any particular form of
photovoltaic material layer.
[0084] In the second step of the method, shown in FIG. 8 as step
S802, an adhesive composition having a low MVTR is formed. The low
MVTR adhesive composition is formed by combining a low MVTR polymer
or copolymer with a silane-modified polymer or copolymer. In one
embodiment, a suitable crosslinking catalyst is included in the
mixture of the low MVTR polymer or copolymer and silane-modified
polymer or copolymer.
[0085] The low MVTR polymer or copolymer may be any of the
materials disclosed above. In one embodiment, the low MVTR polymer
or copolymer is a polymer or copolymer of isobutylene, and in one
embodiment, the low MVTR polymer is polyisobutylene.
[0086] The silane-modified polymer or copolymer may be any of the
polymers or copolymers disclosed above, and the silyl group with
which the polymer or copolymer is modified may be any of the silyl
groups disclosed above. In one embodiment, the polymer or copolymer
comprises propylene, and in one embodiment, the polymer is
amorphous polypropylene. In one embodiment, the silyl group is a
trimethoxysilyl group, a triethoxysilyl group, an alkyl derivative
of the trimethoxysilyl group or the triethoxysilyl group, an
aminoalkoxysilane, or an unsaturated organic silane such as
vinyltrimethoxysilane, or a mixture of any two or more of these
silyl groups, or any of the silanes disclosed herein.
[0087] The step S802 may be carried out in a suitable mixing
apparatus, such as a Banbury mixer. In one embodiment, the mixing
step is carried out under low-moisture conditions, to avoid
premature crosslinking of the silane-modified polymer or copolymer.
In another embodiment, the mixing step is carried out under an
inert gas atmosphere, to avoid premature crosslinking of the
silane-modified polymer or copolymer. The inert gas may be, for
example, nitrogen. In another embodiment, the mixing step is
carried out in an atmosphere of dried air, in which the air has
been dried by, e.g., chilling, to avoid premature crosslinking of
the silane-modified polymer or copolymer. In any embodiment, it is
prudent to handle the silane-modified polymer or copolymer under
conditions which avoid premature crosslinking.
[0088] When the low MVTR adhesive composition has been formed by
thoroughly mixing the ingredients, it is ready to be applied.
[0089] As shown in FIG. 8, in the third step of the present
invention, shown as step S803, the low MVTR adhesive composition is
applied to at least one of the photovoltaic material layer and the
backing panel. As described above, the low MVTR adhesive
composition may be applied to either or both of the front panel or
the backing panel. In an embodiment in which the low MVTR adhesive
is applied to the front panel, it is applied to and over either the
photovoltaic layer or the protective layer, depending on whether
the protective layer is present.
[0090] Application of the low MVTR adhesive composition to the
selected layer or panel may be by any appropriate method known in
the art. For example, the low MVTR adhesive composition may be
applied by spraying, extrusion, spreading with an appropriate
device such as a doctor blade, and other methods such as a transfer
film such as a release liner. A suitable release liner should have
little or no water content. Thus, a suitable material for a release
liner would be a polyolefin or polyethylene treated with a suitable
release agent. In one embodiment, nylon is not suitable for the
release liner, as it may contain residual water or other active
hydrogen sources.
[0091] As shown in FIG. 8, in the fourth step of the present
invention, shown as step S804, the respective layers are brought
together, into sealing contact. Thus, the photovoltaic material
layer, the low MVTR adhesive composition layer and the backing
panel, are brought together to form a single unit. In one
embodiment, the low MVTR adhesive composition is sufficiently tacky
to hold the front panel and the backing panel together. The
photovoltaic material layer, the low MVTR adhesive composition
layer and the backing panel, are brought together in the presence
of at least one of pressure, vacuum and heat. Application of such
forces helps the adhesive to wet the surfaces to which it will be
attached, to provide an intimate, complete attachment. The adhesive
should be applied in a manner so as to avoid the formation of air
pockets or bubbles between the respective front and back panels. As
is known in the art, such air pockets or bubbles can lead to
failure of the solar panel in use.
[0092] As shown in FIG. 8, in the fifth step of the present
invention, shown as step S805, the low MVTR adhesive composition is
crosslinked by a reaction of the silane-modified polymer or
copolymer. In one embodiment, the crosslinking is initiated by
atmospheric moisture. In one embodiment, the low MVTR adhesive
composition further comprises a suitable crosslinking catalyst,
such as any of those disclosed above. In an embodiment including
such a catalyst, the crosslinking reaction is accelerated by the
catalyst. In the absence of the catalyst, the crosslinking reaction
may be quite slow.
[0093] In one embodiment, crosslinking of the low MVTR adhesive
composition is initiated by exposure of the low MVTR adhesive
composition to atmospheric moisture during or after the assembly of
the solar panel.
[0094] In one embodiment, as noted above, the solar panel includes
module wire openings, through which module wires extend. In such an
embodiment, the low MVTR adhesive composition may be inserted into
the module wire openings at a suitable time during assembly of the
solar panel. As noted above, the module wire adhesive may have the
same composition as that of the assembly adhesive, or it may have a
composition which includes a greater proportion of the low MVTR
polymer or copolymer. Both embodiments of the composition used for
the module wire adhesive are referred to in the following as the
module wire adhesive.
[0095] In general, as the solar panel is assembled, the module
wires 118 are first electrically connected to the photovoltaic
layer 102. When the backing panel 108 and the front panel 104
(together with the photovoltaic layer 102) are brought together,
the module wire 118 will extend through the applied adhesive layer
106 and into and through the module wire openings 120. The module
wire openings 120 may be filled with the module wire adhesive 122
at any appropriate time.
[0096] In one embodiment, the module wire adhesive 122 is applied
to the module wire openings 120 at the same time the low MVTR
assembly adhesive 102 is applied to the surface of the backing
panel 108. However, this would require passing the module wire 118
through the adhesive-filled module wire opening 120, which may not
be desirable. In another embodiment, the module wire adhesive 122
is applied to fill the module wire openings 120 after the front
panel 104 and the backing panel 108 have been brought into sealing
contact, but prior to the initiation of crosslinking of the
silane-modified polymer or copolymer. In yet another embodiment,
the module wire adhesive 122 may be applied after crosslinking has
been initiated. In an embodiment in which the crosslinking is
initiated by contact with atmospheric moisture during the assembly,
the module wire adhesive 122 will be applied after initiation of
the crosslinking, since the crosslinking will have been initiated
immediately upon exposure of the low MVTR adhesive composition to
the atmospheric moisture.
[0097] As shown in FIG. 8, once the crosslinking reaction has been
initiated, fabrication of the solar panel may continue. It is noted
that the crosslinking reaction may continue for some time. In one
embodiment, the crosslinking reaction continues for a period of
hours after the crosslinking has been initiated. In another
embodiment, the crosslinking reaction continues for a number of
days or weeks. In another embodiment, the crosslinking reaction
continues indefinitely, slows to a negligible rate and may be
reinitiated or accelerated at some later time as result of the
ingress of moisture into the low MVTR adhesive composition.
EXAMPLES
[0098] The following examples relate to the adhesive compositions
for use with the solar panels of the present invention, their
formulation and testing. While the tests are applied to test
panels, they are considered to be fully applicable to the solar
panels described herein. In each case, the indicated formulations
are prepared from the indicated source materials in the manner
described above, that is, generally in the absence of moisture with
appropriate mixing. These examples are illustrative and not
intended to be limiting in scope.
Formulation Examples
[0099] The following formulation examples include a low MVTR
polymer and a silane-modified APAO in accordance with the present
invention: TABLE-US-00001 Ingredient A B C D E Polyisobutylene
Rubber 16.00 0.00 10.00 33.00 10.00 Filler 34.00 0.00 0.00 33.00
80.00 Hydrocarbon Resin 10.00 0.00 0.00 0.00 0.00 Semi-solid PIB
6.00 10.00 0.00 0.00 0.00 Silane 0.20 0.00 0.00 0.00 0.00 Catalyst
0.05 0.00 0.00 0.05 0.05 Silane-modified APAO 34.00 90.00 90.00
34.00 10.00 TOTAL 100.25 100.00 100.00 100.05 100.05 Ingredient F G
H I J Polyisobutylene Rubber 10.00 10.00 0.00 10.00 10.00 Filler
30.00 30.00 33.00 45.00 40.00 Hydrocarbon Resin 5.00 25.00 15.00 0
10.00 Semi-solid PIB 5.00 0.00 18.00 0.00 5.00 Silane 0.20 0.00
0.00 0.00 0.20 Catalyst 0.05 0.05 0.05 0.05 0.05 Silane-modified
APAO 50.00 35.00 34.00 45.00 35.00 TOTAL 100.25 100.05 100.05
100.05 100.00
[0100] The materials used in the foregoing Formulation Examples are
the following: TABLE-US-00002 Polyisobutylene Rubber BUTYL .RTM.
268 (isobutylene-isoprene copolymer) Filler CaCO.sub.3 Hydrocarbon
Resin FORAL .RTM. 85 or ECR 158 Semi-solid PIB OPPANOL .RTM. B-12
(polyisobutylene) Silane SILQUEST .RTM. A1120 Silane
(aminopropyltrimethoxysiane) Catalyst Dibutyl tin dilaurate (DBTDL)
Silane-modified APAO VESTOPLAST .RTM. 206V
HYPALON.RTM. Based Laminating Adhesive
[0101] TABLE-US-00003 Name Wt. % HYPALON .RTM. H-30 22.8 Semi-solid
polyisobutylene 6.8 Hydrocarbon Resin 11.4 VESTOPLAST .RTM. 206V
26.4 Talc 22.8 Hydrogenated Rosin Ester 3.6 Polymeric polyester
plasticizer 5.7 Tin Catalyst 0.03 Silane 0.5 TOTAL 100.0 HYPALON
.RTM. is a chlorosulfonated polyethylene available from DuPont,
USA.
VAMAC Based Laminating Adhesive
[0102] TABLE-US-00004 Name Wt. % VAMAC .RTM. G (DuPont) 24.1
CaCO.sub.3 17.4 Polymeric polyester plasticizer 6.9 Hydrogenated
Rosin Ester 18.8 VESTOPLAST .RTM. 206V 32.3 Tin Catalyst (Dibutyl
tin dilaurate) 0.03 Silane 0.5 TOTAL 100.0 VAMAC .RTM. G is
believed to be an ethylene/methyl acrylate copolymer containing
carboxyl groups, commercially available from DuPont, USA.
Nitrile Based Laminating Adhesive
[0103] TABLE-US-00005 Name Wt. % NIPOL .RTM. 1072CG (Nippon Zeon)
24.1 Talc 17.4 Polymeric polyester plasticizer 6.9 Hydrogenated
Rosin Ester 18.8 VESTOPLAST .RTM. 206V 32.3 Tin Catalyst 0.03
Silane 0.5 TOTALS 100.0 NIPOL .RTM. 1072G is believed to be a
carboxylic acid functional nitrile rubber, available from Zeon
Chemicals, Inc., Louisville, Ky.
Adhesive Composition with Two Silane-Modified Polymers
[0104] TABLE-US-00006 Name Wt. % Silane-crosslinkable composition
of epichlorohydrin 6.8 rubber and
N-phenylaminopropyltrimethoxysilane* Semi-solid polyisobutylene
22.8 Hydrocarbon Resin 11.4 VESTOPLAST .RTM. 206V 26.4 Talc 22.8
Hydrogenated Rosin Ester 3.6 Polymeric polyester plasticizer 5.7
Tin Catalyst 0.03 Silane 0.5 TOTAL 100.0 *The silane-crosslinkable
composition is prepared by reacting about 5 wt % of the
N-phenylaminopropyltrimethoxysilane with about 95 wt % of the
epichlorohydrin rubber.
Adhesive Composition with Silane-modified Polymer
[0105] TABLE-US-00007 Name Wt. % Silane-crosslinkable composition
of epichlorohydrin 22.8 rubber and
N-phenylaminopropyltrimethoxysilane* Semi-solid polyisobutylene 6.8
Hydrocarbon Resin 11.4 VESTOPLAST .RTM. 750 APAO 26.4 Talc 22.8
Hydrogenated Rosin Ester 3.6 Polymeric polyester plasticizer 5.7
Tin Catalyst 0.03 Silane 0.5 TOTAL 100.0 *The silane-crosslinkable
composition is prepared by reacting about 5 wt % of the
N-phenylaminopropyltrimethoxysilane with about 95 wt % of the
epichlorohydrin rubber.
Adhesive Composition with Two Silane-modified Polymers
[0106] TABLE-US-00008 Name Wt. % Silane-crosslinkable composition
of HYPALON .RTM. 6.8 H-30 rubber and
N-phenylaminopropyltrimethoxysilane* Semi-solid polyisobutylene
22.8 Hydrocarbon Resin 11.4 VESTOPLAST .RTM. 206V 26.4 Talc 22.8
Hydrogenated Rosin Ester 3.6 Polymeric polyester plasticizer 5.7
Tin Catalyst 0.03 Silane 0.5 TOTAL 100.0 *The silane-crosslinkable
composition is prepared by reacting about 5 wt % of the
N-phenylaminopropyltrimethoxysilane with about 95 wt % of the
HYPALON .RTM. H-30 rubber.
Adhesive Composition with Silane-Modified Polymer
[0107] TABLE-US-00009 Name Wt. % Silane-crosslinkable composition
of HYPALON .RTM. 22.8 H-30 rubber and
N-phenylaminopropyltrimethoxysilane* Semi-solid polyisobutylene 6.8
Hydrocarbon Resin 11.4 VESTOPLAST .RTM. 750 APAO 26.4 Talc 22.8
Hydrogenated Rosin Ester 3.6 Polymeric polyester plasticizer 5.7
Tin Catalyst 0.03 Silane 0.5 TOTAL 100.0 *The silane-crosslinkable
composition is prepared by reacting about 5 wt % of the
N-phenylaminopropyltrimethoxysilane with about 95 wt % of the
HYPALON .RTM. H-30 rubber.
Adhesive Composition with Two Silane-modified Polymers
[0108] TABLE-US-00010 Material Batch Wt. % Wt. Silane grafted
copolymer of 441.7 16.4 isobutylene and p-methylstyrene** ECR 158
242.9 9.0 FORAL .RTM. 85 26.3 1.0 CaCO.sub.3 904.5 33.5 B-12 PIB
147.5 5.5 VESTOPLAST .RTM. 930.8 34.5 206V DBTDL 0.9 0 A186 Silane
2.7 0.1 Vinyl Silane 2.7 0.1 TOTAL 2700 100.1
Adhesive Composition with Silane-Modified Polymer
[0109] TABLE-US-00011 Material Batch Wt. % Wt. Silane-grafted
copolymer of 261.8 16.4 isobutylene and p-methylstyrene** ECR 158
144.0 9.0 FORAL .RTM. 85 15.6 1.0 CaCO.sub.3 536.0 33.5 B-12 PIB
87.4 5.5 VESTOPLAST .RTM. 551.6 34.5 750 DBTDL 0.5 0 A186 Silane
1.6 0.1 Vinyl Silane 1.6 0.1 TOTAL 1600.1 100.1 **In the foregoing
examples, the silane-grafted copolymer of isobutylene and
p-methylstyrene is prepared by reacting 88 wt % of a
isobutylene-p-methylstyrene copolymer with 12 wt % of
vinyltrimethoxysilane.
In the foregoing formulation examples, the following raw materials
are used:
Raw Material Definitions
[0110] TABLE-US-00012 Semi-solid Polyisobutylene OPPANOL .RTM. B-12
(BASF) Hydrocarbon Resin ESCOREZ .RTM. 1315 (Exxon) Hydrogenated
Rosin Ester FORAL .RTM. 105 (Hercules) Talc MISTRON .RTM. Vapor
Talc (Luzenac) Calcium Carbonate HUBERCARB .RTM. Q-6 (JM Huber)
Polymeric Polyester Plasticizer PARAPLEX .RTM. G 25 (CP Hall) Tin
Catalyst METACURE .RTM. T12 (Air Products and Chemicals, Inc.)
Vinyltrimethoxysilane A-171 Vinyl Silane (OSi Specialties)
N-phenylaminopropyltrimethoxy Y-9669 (OSi Specialties) silane
Epichlorohydrin Rubber Hydrin CG .RTM. (Zeon Chemicals)
Strength Tests of Adhesive Compositions Comprising Silane-Modified
APAO:
[0111] The following formulation, similar to formulation example A
shown above, is prepared and tested for tensile strength and lap
shear strength after various periods of time following bonding of a
front panel and a back panel during fabrication of an exemplary
solar panel. The tensile strength tests are conducted according to
ASTM D 412-87. The lap shear strength tests are conducted according
to ASTM C 961-87. TABLE-US-00013 Name Ingredient Weight Wt % BUTYL
.RTM. 268 Polyisobutylene Rubber 420 16.3 CaCO.sub.3 Filler 860
33.4 FORAL .RTM. 85 Hydrocarbon Resin 25 1.0 ECR 158 Hydrocarbon
Resin 231 9.0 BASF B-12 Semi-solid polyisobutylene 140 5.4 A1120
Silane Silane 12.5 0.5 DBTDL Catalyst 0.4 0.2 VESTOPLAST .RTM.
Silane-modified APAO 885 34.4 TOTAL 2573.9 100.2
Test Results:
[0112] The foregoing formulation is applied to test substrates and
tested according to the above ASTM methods. The results obtained
are presented below. TABLE-US-00014 Tensile Strength Lap Shear
Strength Strength, psi Strength, psi Time (kg/cm.sup.2) Time
(kg/cm.sup.2) Initial 90.9 (6.39) 2 weeks 90.6 (6.36) 24 hrs 107.4
(7.55) 4 weeks 122.0 (8.58) 4 days 149.3 (10.5) 9 weeks 131.6
(9.25) 6 weeks 201.4 (14.2) 10 weeks 152.0 (10.7) 10 weeks 253.9
(17.8) 12 weeks 161.0 (11.3) 16 weeks 251.4 (17.7) 16 weeks 158.0
(11.1)
[0113] As shown by the test results, in this formulation both the
tensile strength and the shear strength increase over a period of
weeks after fabrication of the test panels.
Comparative Example Silane-Modified APAO vs. Standard APAO:
[0114] The following formulations are prepared as described above,
by combining in a suitable mixing device in the absence of
moisture. TABLE-US-00015 Silane-Modified APAO Standard APAO
Material Batch Wt. % Wt. Batch Wt. % Wt. BUTYL .RTM. 268 441.7 16.4
261.8 16.4 ECR 158 242.9 9.0 144.0 9.0 FORAL .RTM. 85 26.3 1.0 15.6
1.0 CaCO.sub.3 904.5 33.5 536.0 33.5 B-12 PIB 147.5 5.5 87.4 5.5
VESTOPLAST .RTM. 930.8 34.5 0 0 206V VESTOPLAST .RTM. 0 0 551.6
34.5 750 DBTDL 0.9 0 0.5 0 A186 Silane 2.7 0.1 1.6 0.1 Vinyl Silane
2.7 0.1 1.6 0.1 TOTAL 2700 100.1 1600.1 100.1 VESTOPLAST .RTM. 206V
is a silane-modified APAO. VESTOPLAST .RTM. 750 is a standard,
non-silane APAO. Vinyl silane is a silane compound including at
least one vinyl group, for example, vinyltrimethoxy silane. A186
Silane is believed to contain
.beta.-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane, and is
commercially available from OSi Specialties, Inc., Danbury,
Connecticut.
Lap Shear Tests:
[0115] The foregoing formulations are applied to test substrates,
and the lap shear strength is determined according to ASTM C
961-87. The results obtained are shown below. TABLE-US-00016
Silane-Modified APAO Standard APAO Strength, Strength, psi Failure
psi Failure Time (kg/cm.sup.2) Mode Time (kg/cm.sup.2) Mode 24 hr.
116 (8.1) cohesive 24 hr. 89 (6.3) adhe- sive 1 week 122 (8.6)
cohesive 1 week 88 (6.2) adhe- sive 2 weeks 148 (10.4) cohesive 2
weeks 95 (6.7) adhe- sive 4 weeks 142 (10.0) cohesive
[0116] In the foregoing test results, in the "cohesive" failure
mode, the adhesive composition separates internally with adhesion
to both substrates maintained, while in the "adhesive" failure
mode, adhesion of the adhesive composition to one substrate fails,
and all of the adhesive remains on one substrate or the other.
Thus, the foregoing test demonstrates that the silane-modified
polymer or copolymer provides enhanced strength in adhesion to the
test substrate, compared to the same formulation prepared without
the silane-modified polymer or copolymer.
[0117] Although the invention has been shown and described with
respect to certain preferred embodiments, equivalent alterations
and modifications will occur to others skilled in the art upon
reading and understanding this specification and the annexed
drawings. In particular regard to the various functions performed
by the above described integers (components, assemblies, devices,
compositions, steps, etc.), the terms (including a reference to a
"means") used to describe such integers are intended to correspond,
unless otherwise indicated, to any integer which performs the
specified function of the described integer (i.e., that is
functionally equivalent), even though not structurally equivalent
to the disclosed structure which performs the function in the
herein illustrated exemplary embodiment or embodiments of the
invention. In addition, while a particular feature of the invention
may have been described above with respect to only one of several
illustrated embodiments, such feature may be combined with one or
more other features of the other embodiments, as may be desired and
advantageous for any given or particular application.
* * * * *