U.S. patent application number 14/608263 was filed with the patent office on 2015-05-21 for barrier materials for mirror assemblies.
The applicant listed for this patent is HONEYWELL INTERNATIONAL INC.. Invention is credited to Awdhoot Vasant Kerkar, Sudip Mukhopadhyay, David Nalewajek, Desaraju Varaprasad.
Application Number | 20150140328 14/608263 |
Document ID | / |
Family ID | 46637122 |
Filed Date | 2015-05-21 |
United States Patent
Application |
20150140328 |
Kind Code |
A1 |
Mukhopadhyay; Sudip ; et
al. |
May 21, 2015 |
BARRIER MATERIALS FOR MIRROR ASSEMBLIES
Abstract
Provided herein is a reflective optical construction containing
a fluoropolymer barrier layer, wherein the fluoropolymer is
selected from the group consisting of homopolymers and copolymers
of at least one tetrafluoropropene or pentafluoropropene,
preferably 2,3,3,3-tetrafluoropropene. Also disclosed is a method
of forming a reflective optical construction including (a) applying
a barrier layer comprising one or more fluoropolymers selected from
the group consisting of homopolymers and copolymers of at least one
tetrafluoropropene or pentafluoropropene, and (b) curing.
Inventors: |
Mukhopadhyay; Sudip;
(Berkeley, CA) ; Varaprasad; Desaraju; (Sunnyvale,
CA) ; Nalewajek; David; (West Seneca, NY) ;
Kerkar; Awdhoot Vasant; (Rockaway, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HONEYWELL INTERNATIONAL INC. |
Morristown |
NJ |
US |
|
|
Family ID: |
46637122 |
Appl. No.: |
14/608263 |
Filed: |
January 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13397208 |
Feb 15, 2012 |
8968877 |
|
|
14608263 |
|
|
|
|
61443544 |
Feb 16, 2011 |
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Current U.S.
Class: |
428/339 ;
427/164; 428/421 |
Current CPC
Class: |
C09D 127/12 20130101;
G02B 1/14 20150115; B05D 3/02 20130101; F24S 2023/86 20180501; G02B
5/0808 20130101; G02B 1/105 20130101; Y02E 10/40 20130101; Y10T
428/26 20150115; F24S 23/82 20180501; Y02E 10/50 20130101; B05D
1/02 20130101; F24S 40/40 20180501; Y10T 428/269 20150115; Y10T
428/3154 20150401 |
Class at
Publication: |
428/339 ;
428/421; 427/164 |
International
Class: |
G02B 1/14 20060101
G02B001/14; G02B 5/08 20060101 G02B005/08; C09D 127/12 20060101
C09D127/12 |
Claims
1-20. (canceled)
21. A reflective optical construction comprising: (a) an optically
transparent substrate containing a reflective layer disposed on the
back of said substrate; and (b) a barrier layer disposed on a
portion of at least one surface of the reflective layer, the
barrier layer comprising a fluoropolymer, wherein said
fluoropolymer is a copolymer of monomer units selected from the
group consisting of tetrafluoropropenes and pentafluoropropenes,
and wherein said barrier layer protects said reflective layer from
corrosion.
22. The reflective optical construction of claim 21, wherein said
fluoropolymer is represented by Formula (I): ##STR00004## wherein n
is a number from about 10 to about 2,500; and R.sub.1, R.sub.2, and
R.sub.3 are independently selected from H and F.
23. The reflective optical construction of claim 22, wherein n is a
number from about 15 to about 2,000.
24. The reflective optical construction of claim 21, wherein said
fluoropolymer has a molecular weight between about 2,000 and about
200,000 Daltons.
25. The reflective optical construction of claim 21, wherein said
fluoropolymer is a copolymer derived from a tetrafluoropropene
compound.
26. The reflective optical construction of claim 21, wherein said
fluoropolymer is a copolymer derived from a compound selected from
the group consisting of HFO-1234yf, HFO-1234ze, and HFO-1225.
27. The reflective optical construction of claim 26, wherein said
fluoropolymer is a copolymer derived from HFO-1234yf.
28. The reflective optical construction of claim 26, wherein said
fluoropolymer is a copolymer derived from HFO-1234ze.
29. The reflective optical construction of claim 21, wherein the
thickness of said fluoropolymer barrier layer is between about 1
micron and about 3,000 microns.
30. A reflective optical construction comprising: (a) an optically
transparent substrate containing a reflective layer disposed on the
back of said substrate; and (b) a barrier layer disposed on at
least a portion of at least one surface of the reflective layer,
the barrier layer consisting essentially of at least one
fluoropolymer selected from the group consisting of copolymers
derived from a tetrafluoropropene compound, and copolymers derived
from a pentafluoropropene compound, wherein the fluoropolymer has a
molecular weight between about 2,000 and about 200,000 Daltons;
wherein said barrier layer protects said reflective layer from
corrosion.
31. The reflective optical construction of claim 30, wherein said
fluoropolymer has a molecular weight between about 10,000 and about
100,000 Daltons.
32. The reflective optical construction of claim 30, wherein said
tetrafluoropropene compound or pentafluoropropene compound is
selected from the group consisting of HFO-1234yf, HFO-1234ze, and
HFO-1225.
33. The reflective optical construction of claim 32, wherein said
tetrafluoropropene compound is HFO-1234yf.
34. The reflective optical construction of claim 32, wherein said
tetrafluoropropene compound is HFO-1234ze.
35. A method of forming a reflective optical construction
comprising: (a) applying a barrier coating solution to a reflective
layer disposed on the back of an optically transparent substrate,
the barrier coating solution comprising at least one fluoropolymer
selected from the group consisting of copolymers derived from a
tetrafluoropropene compound and copolymers derived from a
pentafluoropropene compound, wherein the fluoropolymer has a
molecular weight between about 2,000 and about 200,000 Daltons; and
(b) curing the applied barrier coating solution to form a barrier
layer on the reflective layer.
36. The method of claim 35, wherein the barrier coating solution is
applied by spray coating.
37. The method of claim 35, wherein the curing step comprises
heating to a temperature between about 60.degree. C. and about
350.degree. C.
38. The method of claim 35, wherein said tetrafluoropropene
compound or pentafluoropropene compound is selected from the group
consisting of HFO-1234yf, HFO-1234ze, and HFO-1225.
39. The method of claim 38, wherein said tetrafluoropropene
compound is HFO-1234yf.
40. The method of claim 35, wherein said barrier coating solution
further comprises an organic solvent.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is related to and claims the priority
benefit of U.S. Provisional Application No. 61/443,544, filed on
Feb. 16, 2011, which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to fluoropolymer barrier
layers for the protection of reflective layers in mirror
assemblies.
BACKGROUND OF THE INVENTION
[0003] The basic principle underlying solar-thermal electricity
generation (concentrated solar power--CSP) is the following: energy
from the sun either directly or indirectly heats water, which
vaporizes, and the resulting steam drives a turbine whose motion is
converted into electricity in a generator. One advantage of the
power generated by CSP units is that it is completely CO.sub.2
free, and therefore has a negligible carbon footprint.
[0004] In order to achieve the high temperatures required to heat
the water, the solar radiation must be concentrated. CSP plants
concentrate solar energy using mirrors distributed across a small
area. The four major CSP technologies include parabolic troughs,
linear fresnel, power towers, and dish/engine. Parabolic trough
collectors represent the most advanced technology for concentrating
solar energy. These troughs are typically more than 1,300 feet in
length and are made up of parabolically shaped mirror segments. The
curvature of the mirrors allows them to concentrate the sun's
direct beam radiation onto a linear receiver.
[0005] Current parabolic trough power plants use glass mirror
panels. The mirrors are typically second-surface silvered glass
mirrors, which means that the reflective metal layer, preferably a
silver layer, is on the backside of the glass. The glass is
typically a 4-millimeter-thick, special low iron, or white glass,
with a high transmittance. These mirrors will frequently have a
solar-weighted specular reflectivity of about 93.5%. Heretofore, a
special multilayer paint coating was commonly used to protect the
reflective metal layer on the back of the mirror. In a typical
configuration, each mirror panel is approximately 2 square meters
in area.
[0006] The mirrors on most CSP systems are made of silvered glass
because of silver's high solar reflectivity (93%), relatively low
cost, and high durability. The most common construction technique
involves laminating a thin, silver mirror to a heavier glass
backing structure. Other materials that have been used as the
reflectors in solar concentrators include silvered polymer films
and augmented aluminum reflectors. The reflective layer may also
include a copper back layer for long term durability.
[0007] Both the silver reflective layer and copper back layers are
prone to air oxidation. Moisture can also degrade these
metal-containing layers, as water facilitates the corrosion. In
particular, such external elements can cause the degradation and
destruction of the silver or other metal contained in the
reflective layer over time, as evidenced by tarnishing,
discoloration, breakdown, and delamination, resulting in the loss
of the mirror's reflectivity. Thus, as appreciated in the current
state of the art, the metal layers have heretofore been commonly
protected with at least two paint layers plus a UV/moisture
protection layer backing the paint layers. The paints typically
used for this purpose are lead-based paints.
[0008] Applicants have come to appreciate an incentive to remove
the paint, and in particular the lead-containing components,
completely for environmental reasons. High cost is also an issue
for multi-layer coatings that have been heretofore used. Therefore,
applicants have come to appreciate a need and to formulate a desire
to replace the multiple paint layers heretofore commonly used with
a layer of a single coating or film that can provide the barrier
protection. The present invention addresses these needs and
desires, among others.
SUMMARY
[0009] Provided herein are barrier coatings, barrier films and
barrier coating solutions, reflective optical constructions that
employ barrier coatings/films, and improved processes for preparing
barrier coatings, barrier films and barrier coating solutions.
[0010] One aspect of the present invention provides reflective
optical constructions comprising an optically transparent substrate
containing a reflective layer disposed on the back of the substrate
and a barrier coating or film disposed on at least a portion of,
and preferably over the entirety, of at least the back surface of
the reflective layer. In one embodiment, the barrier coating/film
is formed from a polymer, and preferably a thermosetting polymer,
that contains a substantial component comprising fluoropolymer, and
even more preferably a substantial component of which comprises a
polymer or polymeric segment represented by the following Formula
(I):
##STR00001##
wherein n is from about 10 to about 2,500, R.sub.1, R.sub.2, and
R.sub.3 are independently selected from H and F. Preferably in
certain embodiment, the polymer is a polymer substantially
according to Formula (I) having a molecular weight of from about
2,000 and about 200,000 Daltons.
[0011] Another aspect of the present invention provides a barrier
coating or film comprising at least one polymer comprising, and
preferably consisting essentially of segments that are
homopolymeric, copolymeric, terpolymeric and the like which are
derived in at least substantial proportion from a
tetrafluoropropene or a pentafluoropropene monomeric compound. In
one embodiment, the tetrafluoropropene or pentafluoropropene
monomer includes at least one compound according to formula
CF.sub.3CR.sub.1.dbd.CR.sub.2R.sub.3, wherein R.sub.1, R.sub.2, and
R.sub.3 are each independently selected from H and F.
[0012] Another aspect of the present invention provides methods of
forming a reflective optical construction by applying a barrier
coating solution onto a reflective layer. In certain preferred
embodiment, the applying step comprises applying a barrier coating
solution onto a reflective layer that is disposed on the back of an
optically transparent substrate. The methods also preferably
comprise curing the coating solution to form a cured coating or
protective film on the reflective layer. In certain embodiments,
the barrier coating solution and/or cured coating includes at least
one polymer selected from the group consisting of homopolymers,
copolymers, terpolymers and the like that comprise in substantial
proportion, and preferably consist essentially of polymeric
material derived from tetrafluoropropene monomer,
pentafluoropropene monomer, and combinations of these. In certain
preferred embodiments, curing is performed at a temperature of from
about 60.degree. C. to about 350.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic depiction of an art-standard
multi-layer mirror assembly.
[0014] FIG. 2 is a schematic depiction of an embodiment of a
multi-layer mirror assembly containing a barrier coating in
accordance with the present invention.
[0015] FIG. 3 is a schematic depiction of an embodiment of a
multi-layer parabolic mirror assembly containing a barrier coating
according to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0016] Surprisingly, it has now been found that fluorinated
polymers, preferably fluoropolymers that contain substantial
portions or segments, formed from tetrafluoropropene monomer,
and/or pentafluoropropene monomer, particularly
2,3,3,3-tetrafluoropropene ("HFO-1234yf") can be used
advantageously as a protective layer or film for the reflective
layer in mirror assemblies, preferably as a replacement for and
instead of multiple paint layers, as well as the UV/Moisture
adhesive layers. The fluorinated polymers of the present invention
can also be used as a thin coating on the upper glass surface as a
barrier layer.
[0017] As used herein, the term "reflective optical construction"
encompasses any mirror-like assembly which redirects
electromagnetic radiation, particularly sunlight. Preferred aspects
of the present invention provide a reflective optical construction
containing a barrier layer comprising a polymer as described
herein, and preferably a fluoropolymer, and even more preferably a
polymer formed according to Formula (I), wherein the reflective
optical construction demonstrates a substantially unchanged level
of optical performance and excellent durability after exposure to
at least one of, and preferably each of, the following performance
test conditions: (1) 85.degree. C. at 85 relative humidity for
1,000 hours; (2) standard QUV Accelerated Weathering testing
conditions (e.g., ASTM G154 and/or AATCC TM186); and (3) 45.degree.
C. at 100% relative humidity for 1,000 hours. In preferred
embodiments, the polymer and preferably the fluoropolymer as
applied produces a contact angle in the range of from about 110 to
about 130 degrees.
[0018] In certain embodiments, the reflective optical construction
is included within a multi-layer CSP mirror assembly. A typical CSP
mirror assembly of the state of the art is presented schematically
in FIG. 1. The multiple layers typically include a substrate 1, a
reflective layer 2, a copper layer 3, at least two lead paint
layers 4-5, a UV/moisture barrier adhesive layer 6, an adhesive
layer 7, and a support 8. The substrate has a first side for
gathering solar energy and a second side opposite the first side.
The substrate may be flat or parabolically curved if intended to
focus the solar radiation. The reflective layer is disposed on the
back of the second side of the substrate and reflects the solar
energy gathered by the first side being transmitted through the
substrate to the second side. The lead paint layers 4-5 typically
have lead contents of 2.5-20% for the first paint layer, and 1-10%
for the second paint layer. Taken together, the lead paint layers
4-5 and the UV/moisture barrier adhesive layer 6 are designed to
shield the reflective layer 2 and copper layer 3 from UV radiation,
gases, and moisture.
[0019] As shown in FIG. 2, Applicants have surprisingly discovered
that the reflective layers of such optical constructions can be
protected by a barrier layer, e.g., a coating or film, that
comprises, and even more preferably consists essentially of a
barrier coating 5, which in preferred embodiments is a single,
unitary layer or coating of the present fluoropolymer. Such a
construction according to the present invention provides
substantial economic and environmental advantages. For example, the
elimination of a potential lead pollutant in the lead improves the
environmental impact caused by CSP mirror assemblies.
[0020] The barrier coating also protects the reflective optical
construction or mirror assembly from degradation caused by exposure
to environmental factors, including gases and/or water. Atmospheric
gases such as oxygen and ozone corrode the metal layers,
particularly the silver reflective layer. Further, gaseous
pollutants found in the environment, such as sulfur oxides and
nitrogen oxides, can contribute to corrosion. In addition, moisture
facilitates the corrosion process. However, the fluoropolymeric
barrier coating according to the present invention is capable of
effectively protecting the reflective layer from the effects of
such environmental factors.
[0021] With reference to FIG. 2, in one aspect the present
invention provides a mirror assembly including a substrate 11, a
reflective layer 12 optionally including a copper back layer 13 and
an adhesive layer 14, a barrier coating layer 15, an adhesive layer
16, and a support 17. The substrate may be a low-iron glass
substrate or a barrier coated low-iron glass substrate and having a
thickness of about 1 mm to about 4 mm. The reflective layer may
comprise any metal which provides a mirrored surface and reflects
incident light, and in preferred embodiments has a thickness of
about 100 microns to about 5 mm. Preferred metals for the metal
layer include silver and aluminum. The support may be formed of
glass, ceramic, stainless steel, aluminum, or other material
capable of bearing the weight of the mirror assembly.
[0022] FIG. 3 demonstrates a preferred embodiment in which the
reflective optical construction is in a parabolic form. The
reflective layer 12 is disposed on the back of the substrate 11,
and the barrier coating layer 15 encloses the reflective layer 12
so as to prevent any moisture or corrosive gases from contacting
the reflective layer 12.
[0023] In certain embodiments, the barrier coating includes at
least one polymer represented by Formula (I):
##STR00002##
wherein n is from about 10 to about 2,500, R.sub.1, R.sub.2, and
R.sub.3 are independently selected from H and F, and the polymer
has a molecular weight from about 2,000 and about 200,000 Daltons,
preferably from about 10,000 and about 100,000 Daltons, and more
preferably from about 23,000 and about 150,000 Daltons.
[0024] Preferred barrier coatings maybe formed by any methods know
by those skilled in the art. In preferred aspects, the formation
methods comprise polymerizing a fluorocarbon compound of the
general formula CF.sub.3CR.sub.1.dbd.CR.sub.2R.sub.3, wherein
R.sub.1, R.sub.2, and R.sub.3 are independently H or F, in the
presence of an initiator and under suitable reaction conditions.
After forming the polymer, acid may be added to precipitate the
polymer. The precipitated polymer may then be filtered, dried, and
combined with another solvent to form a barrier coating solution.
In preferred embodiments, the barrier coating solution is then
applied to a reflective layer disposed on a substrate and cured to
form a reflective optical construction.
[0025] A variety of commercially available hydrofluoro-olefins
("HFOs") may be used as the monomer(s) to form the polymer.
Suitable HFOs may have the general formula
CF.sub.3CR.sub.1.dbd.CR.sub.2R.sub.3, wherein R.sub.1, R.sub.2, and
R.sub.3 are each selected from H and F. Examples of suitable HFOs
include tetrafluoropropene compounds and pentafluoropropene
compounds. A particularly suitable tetrafluoropropene compound is
2,3,3,3-tetrafluoropropene ("HFO-1234yf"), which forms a polymer
having the following Formula (II):
##STR00003##
wherein n=10 and about 2,500.
[0026] Other suitable tetrafluoropropene compounds include
HFO-1234zf and HFO-1234ze. Suitable pentafluoropropene compounds
include HFO-1225. Stereoisomers of any of the foregoing compounds
may also be suitable.
[0027] In one embodiment, the compounds referenced above may be
copolymerized with additional co-monomer compounds, and in
particular with additional halogenated co-monomers. Fluorinated
co-monomer compounds include, without limitation, fluoroolefins,
fluorinated vinyl ethers and fluorinated dioxoles. Monomers
suitable as co-monomers include, without limitation, acrylic acid
and esters thereof, methacrylic acid and esters thereof, ethylene,
propylene, butylene, fluoroethylene (vinyl fluoride),
1,1-difluoroethylene (vinylidene fluoride, or vinylidene
difluoride), 1,2-difluoroethylene, trifluoroethylene,
tetrafluoroethylene, chlorotrifluoroethylene, chloroethylene,
1,1-dichloroethylene, 1,2-dichloroethylene, trichloroethylene,
tetrachloroethylene, hexafluoropropylene, hexfluoroisobutylene,
perfluorobutyl ethylene, perfluoro(methyl vinyl ether),
perfluoro(ethyl vinyl ether), perfluoro(propyl vinyl ether),
perfluoro-2,2-dimethyl-1,3-dioxole and
perfluoro-2-methylene-4-methyl-1,3-dioxolane. In certain
embodiments, preferred co-monomers include ethylene, propylene,
butylene, fluoroethylene, 1,1-difluoroethylene,
1,2-difluoroethylene, trifluoroethylene, tetrafluoroethylene,
chlorotrifluoroethylene, chloroethylene, 1,1-dichloroethylene,
1,2-dichloroethylene, trichloroethylene, and/or
tetrachloroethylene. Co-monomers can comprise about 1 to about 90%
of the fluoropolymer, preferably about 5 to about 75%, and more
preferably about 10 to about 50%.
[0028] Polymerization is carried out in the presence of one or more
free-radical initiators. Suitable initiators include
azobiscyanoacrylates, aliphatic peresters such as t-butyl
percotoate and t-amyl peroctoate, aliphatic peroxides such as
t-butyl peroxide, aliphatic hydroperoxides such as t-butyl
hydroperoxide, persulfates such as sodium persulfate, potassium
persulfate, ammonium persulfate, and iron persulfate, and
combinations of the foregoing. A persulfate initiator may be
included in the reaction solution at a concentration of less than
20 weight %, more particularly less than 12 weight %, and even more
particularly less than 1.0 weight % based on the total weight of
the monomer.
[0029] The reaction between the polymer and initiator may be
carried out in a solution including water, buffer, and/or a
surfactant. Suitable buffers include Na.sub.2HPO.sub.4,
NaH.sub.2PO.sub.4, FeSO.sub.4, and combinations thereof.
Particularly suitable buffers include sodium phosphate dibasic
hepthahydrate, sodium phosphate monobasic, ferrous sulfate
heptahydrate, and combinations thereof. Suitable surfactants
include fluorosurfactants, more particularly perfluorinated
carboxylic acid surfactants such as C.sub.8HF.sub.15O.sub.2 and
C.sub.7F.sub.15CO.sub.2(NH).sub.4. Reducing agents such as
Na.sub.2S.sub.2O.sub.5 and additional solvents/diluents may also be
added.
[0030] The reaction may be carried out in, for example, an
autoclave or jacketed stirred tank reactor ("STR") via a batch or
semi-batch mode at a temperature of from about 20.degree. C. to
about 85.degree. C., preferably of from about 40.degree. C. to
about 60.degree. C. Reaction times may range from about 30 minutes
to about 48 hours, preferably from about 10 to about 24 hours. The
resulting polymer may have a molecular weight between about 2,000
and 200,000 Daltons, preferably between about 10,000 to about
100,000 Daltons.
[0031] In one embodiment, a minor amount of peroxide as a finishing
step may be added after the polymerization reaction has
substantially ended. Such a finishing step has the purpose of
removing unreacted monomers and aids. After completing
polymerization, the polymer is precipitated from the emulsion by
adding acid. The polymer precipitate is then filtered and
dried.
[0032] A barrier coating solution is then formed by dissolving or
dispersing the polymer in a suitable organic solvent. Suitable
organic solvents generally include, for example, acetone, methyl
acetate, ethyl acetate, and various ketones. The amount of solvent
used to form the coating composition can be varied such that the
solids concentration ranges from about 1 to about 25 weight
percent, preferably from about 1 to about 10 weight percent, and
more preferably from about 1 to about 5 weight percent depending
upon the application method and/or performance requirements. In
some embodiments, there may be manufacturing advantages to forming
a coating concentrate, followed by diluting to the desired coating
concentration. In alternate embodiments, dilution could occur prior
to or during the initial mixing stage.
[0033] The barrier coating solution may be applied onto the
reflective optical construction by a variety of generally known
coating methods including spin-on, slot die, spray, dip, roller,
and other coating techniques. For dip coating, a solids
concentration of about 10 to about 20 weight percent may be
suitable. For other coating methods such as spin, slot die, and
spray, a lower solids concentration of about 1 to about 5 weight
percent may be suitable. Embodiments of the present invention may
be particularly suitable for spray application due to the
relatively small polymer particle size of the fluoropolymer. The
viscosity of the resulting coating solution may vary from between
0.5 cP to greater than 500 cP, preferably from about 0.5 cP to
about 10 cP, and more preferably from about 0.75 cP to about 2.0
cP.
[0034] The barrier coating solution is applied to at least a
portion of a surface of the reflective layer. The barrier coating
solution is then cured to form a barrier coating on the reflective
layer. The barrier coating solution can be subjected to a low
temperature heat curing step, ranging from about 60.degree. C. to
about 350.degree. C., preferably from about 150.degree. C. to about
325.degree. C., and more preferably from about 200.degree. C. to
about 250.degree. C. Curing may be carried between 1 minute and
about 1 hour, preferably from about 1 minute to about 15 minutes.
The resulting coating may be, according to certain embodiments,
non-porous. In certain embodiments, the barrier coating solution is
applied onto a previously coated reflective layer.
[0035] The thickness of the barrier coating in the reflective
optical construction is in the range of from about 1 micron to
about 3 millimeters, preferably about 5 to about 1,000 microns,
more preferably from about 10 to about 500 microns, and even more
preferably from about 50 to about 100 microns. In order to achieve
the appropriate thickness, two or more layers of the same or
different barrier coatings can be applied back to back, with or
without an adhesive layer between.
[0036] The barrier coating may also comprise an adhesive. In order
to prevent corrosion in reflective optical constructions,
adhesives, particularly those which come in direct contact with the
reflective layers containing one or more metals, should not be
corrosive to those metals. For example, the adhesive should be low
in halide ions, particularly chloride, which corrodes both copper
and silver.
[0037] In certain embodiments, a preformed sheet or film comprising
polymers as described above is glued to the back of the reflective
coating using an adhesive. Other embodiments of the invention may
utilize any suitable method for applying a fluoropolymer to a
surface, as known by those skilled in the art. The barrier coatings
according to this invention may be used in other applications. It
is also within the scope of the invention that other layers may be
provided in the mirror assembly so that the barrier coating is
considered disposed on the glass substrate even if other layers are
provided therebetween.
EXAMPLES
[0038] The following example is provided for the purpose of
illustrating the present invention, but without limiting the scope
thereof.
Example 1
[0039] A homopolymer of 2,3,3,3-tetrafluoropropene is dissolved in
ethyl acetate, with or without added adhesive, to form various
coating compositions having polymer concentrations between about 1
wt % and about 20 weight %. The resulting barrier coating solutions
are applied by spray coating, to the metal layer of glass mirror
assemblies containing either a silver reflective layer or both a
silver reflective layer and a copper back layer, and the resulting
mirror assemblies are cured by heating. The barrier coatings thus
made are hydrophobic, demonstrating a water contact angle of
110-130 degrees, which indicates a high level of moisture
resistance. The exemplified reflective optical construction is
found to maintain a substantially unchanged level of optical
performance and demonstrates excellent durability under three
different test conditions: (1) 85% relative humidity ("RH") at
85.degree. C. for 1,000 hours; (2) standard QUV Accelerated
Weathering testing conditions (e.g., ASTM G154 and/or AATCC TM186);
and (3) 100% RH at 45.degree. C. for 1,000 hours.
* * * * *