U.S. patent application number 13/786516 was filed with the patent office on 2013-12-19 for coated sheet materials having high solar reflective index and corrosion resistance, and methods of making same.
This patent application is currently assigned to PPG Industries Ohio, Inc.. The applicant listed for this patent is PPG INDUSTRIES OHIO, INC.. Invention is credited to Carole A. Conley, Brian K. Rearick, William H. Retsch, JR., Irina Schwendeman.
Application Number | 20130337258 13/786516 |
Document ID | / |
Family ID | 49756179 |
Filed Date | 2013-12-19 |
United States Patent
Application |
20130337258 |
Kind Code |
A1 |
Schwendeman; Irina ; et
al. |
December 19, 2013 |
COATED SHEET MATERIALS HAVING HIGH SOLAR REFLECTIVE INDEX AND
CORROSION RESISTANCE, AND METHODS OF MAKING SAME
Abstract
Coated sheet materials having high solar reflective index and
corrosion resistance, and methods of making such coated sheet
materials, are disclosed. In certain embodiments, the sheet
materials comprise metal such as galvanized steel roofing sheets,
and the coating is deposited from a latex resin.
Inventors: |
Schwendeman; Irina;
(Wexford, PA) ; Retsch, JR.; William H.; (Castle
Shannon, PA) ; Rearick; Brian K.; (Allison Park,
PA) ; Conley; Carole A.; (Saxonburg, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PPG INDUSTRIES OHIO, INC. |
Cleveland |
OH |
US |
|
|
Assignee: |
PPG Industries Ohio, Inc.
Cleveland
OH
|
Family ID: |
49756179 |
Appl. No.: |
13/786516 |
Filed: |
March 6, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61661532 |
Jun 19, 2012 |
|
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|
Current U.S.
Class: |
428/327 ;
427/178; 427/388.1; 427/388.4; 428/336; 428/461 |
Current CPC
Class: |
Y10T 428/265 20150115;
C09D 7/61 20180101; C08K 3/04 20130101; C09D 5/004 20130101; E04D
5/10 20130101; C09D 5/08 20130101; Y10T 428/31692 20150401; Y10T
428/254 20150115; C09D 7/48 20180101; C09D 5/028 20130101 |
Class at
Publication: |
428/327 ;
428/336; 428/461; 427/388.1; 427/388.4; 427/178 |
International
Class: |
E04D 5/10 20060101
E04D005/10 |
Claims
1. A coated metal sheet comprising: a metal substrate; and a cured
coating covering at least a portion of the metal substrate,
wherein: (a) the cured coating: (i) is deposited from a composition
comprising a latex resin, (ii) is substantially clear, (iii) is
substantially free of reflective pigments, and (iv) has a dry film
thickness of at least 1 micron; and (b) the coated metal sheet has
a solar reflective index of at least 65 and a corrosion resistance
of at least 500 h with no corrosion spots when subjected to an
ASTMB117 salt spray test.
2. The metal sheet of claim 1, wherein the latex resin is
self-crosslinking.
3. The metal sheet of claim 1, wherein the latex resin is prepared
from at least one vinyl aromatic monomer.
4. The metal sheet of claim 1, wherein the latex resin has an
average particle size of from 50 to 300 nm.
5. The metal sheet of claim 1, wherein the cured coating has a dry
film thickness of at least 2 microns.
6. The metal sheet of claim 1, wherein the cured coating has a dry
film thickness of from 3 to 20 microns.
7. The metal sheet of claim 1, wherein the cured coating further
comprises a coalescing agent, wax, viscosity enhancing agent and/or
a thickening agent.
8. The metal sheet of claim 1, wherein the cured coating further
comprises from 0.5 to 3 weight percent wax.
9. The metal sheet of claim 1, wherein the cured coating is
substantially free of chrome.
10. The metal sheet of claim 1, wherein the cured coating is
substantially free of metal phosphate.
11. The metal sheet of claim 1, wherein the cured coating comprises
at least one chromate.
12. The metal sheet of claim 1, wherein the cured coating further
comprises a colored pigment or a tint.
13. The metal sheet of claim 1, wherein the cured coating further
comprises up to 6 weight percent of a reflective pigment.
14. The metal sheet of claim 1, wherein the cured coating further
comprises graphenic carbon particles.
15. The rubber formulation of claim 14, wherein the cured coating
comprises up to 5 weight percent of the graphenic carbon
particles.
16. The metal sheet of claim 1, wherein the metal is in the form of
a coil.
17. The metal sheet of claim 1, wherein the metal substrate
comprises a metal roofing sheet.
18. The metal sheet of claim 1, wherein the metal substrate
comprises galvanized steel.
19. The metal sheet of claim 1, wherein the coated metal sheet has
a solar reflectance of at least 65.
20. The metal sheet of claim 1, wherein the metal sheet has a
thermal emittance of at least 40 percent.
21. A coated roof sheeting material comprising: a sheet metal
substrate; and a coating covering at least a portion of the sheet
metal substrate, wherein the coating consists essentially of a
cured latex resin, and wherein the coated roof sheeting material
has a solar reflectance of at least 65 percent, a thermal emittance
of at least 40 percent, and a corrosion resistance of at least 500
h with no corrosion spots when subjected to an ASTMB117 salt spray
test.
22. The coated roof sheeting material of claim 21, wherein the
sheet metal substrate comprises galvanized steel.
23. The coated roof sheeting material of claim 22, wherein the
galvanized steel is in the form of a coil.
24. The coated roof sheeting material of claim 21, wherein the
coating is deposited from a composition comprising a latex resin
and has a dry film thickness of at least 1 micron.
25. A method of coating a sheet metal substrate comprising:
applying a coating composition comprising a latex resin that is
substantially free of reflective pigments to the sheet metal
substrate at a wet film thickness of at least 1 micron; and curing
the coating composition to produce a coated metal sheet having a
solar reflective index of at least 65 and a corrosion resistance of
at least 500 h with no corrosion spots when subjected to an
ASTMB117 salt spray test.
26. The method of claim 25, wherein the coating composition is
waterborne.
27. The method of claim 25, wherein the coating composition further
comprises a coalescing agent, wax, viscosity enhancing agent and/or
thickening agent.
28. The method of claim 25, wherein the coating composition has a
viscosity of at least 10 seconds measured by a No. 4 Zahn cup at
room temperature.
29. The method of claim 25, wherein the latex resin has a glass
transition temperature of less than 50.degree. C.
30. The method of claim 25, wherein the coating composition
comprises less than 5 weight percent volatile organic solvent.
31. The method of claim 25, wherein the coating composition has a
VOC of less than 1.5.
32. The method of claim 25, wherein the coating composition is
hydrophobic.
33. The method of claim 25, wherein the coating composition is
substantially free of chrome and metal phosphate.
34. The method of claim 25, wherein the coating composition is
applied by roll coating.
35. The method of claim 34, wherein the coating composition is
applied at a rate of at least 200 ft/min.
36. The method of claim 25, wherein the coating is cured at a
temperature of less than 250.degree. for a time of less than 10
seconds.
37. The method of claim 25, further comprising forming the coated
metal sheet into a coil.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 61/661,532 filed Jun. 19, 2012, which
is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to coated sheet materials
having high solar reflective index and corrosion resistance, and
methods of making such coated sheet materials.
BACKGROUND OF THE INVENTION
[0003] Sheet materials used in architectural and other applications
often require corrosion resistant properties. For example, steel
and other types of metal roofing sheet materials must withstand
exposure to environmental conditions for extended periods of time.
Galvanized steel roofing sheets have conventionally been
pre-treated with chromium-containing compositions to increase
corrosion resistance. Such pretreatments may be conducted on long
strips of the steel, which are then coiled into rolls for
subsequent use.
[0004] Galvanized steel and other types of metal roofing materials
may have high solar reflectance properties, but they tend to heat
up when exposed to sunlight due to their low thermal emittance
properties. As a result of such solar heating, the underlying
structures can require significant amounts of energy to cool, e.g.,
by air conditioning.
[0005] Several recent US and state government regulations require
metal roofing to meet certain solar reflective index values to
avoid overheating. Solar reflective index (SRI) is calculated based
upon the combination of solar reflectance and thermal emittance,
with an SRI value of 65, 70 or higher being required to meet
certain government regulations. Solar reflectance is measured as a
percentage of solar radiation in the visible, infrared and
ultraviolet regions of the electromagnetic spectrum that is
reflected from a surface, with a value of 0 or 0% corresponding to
zero reflectance and a value of 1 or 100% corresponding to total
reflectance. Thermal emittance is measured as the ability of a
surface to shed heat, with a value of 0 or 0% corresponding to zero
thermal emittance and a value of 1 or 100% corresponding to total
thermal emittance. In order to reduce overheating, metal roofing
with both relatively high solar reflectance and thermal emittance
is desired.
[0006] Conventional metal roofing fails to meet certain government
energy regulations, and the use of conventional pretreatments
decreases the solar reflective index below that of the untreated
metal.
SUMMARY OF THE INVENTION
[0007] An aspect of the invention provides a coated metal sheet
comprising a metal substrate, and a cured coating covering at least
a portion of the metal substrate, wherein: (a) the cured coating:
(i) is deposited from a composition comprising a latex resin, (ii)
is substantially clear, (iii) is substantially free of reflective
pigments, and (iv) has a dry film thickness of at least 1 micron;
and (b) the coated metal sheet has a solar reflective index of at
least 65 and a corrosion resistance of at least 500 h with no
corrosion spots when subjected to an ASTMB117 salt spray test.
[0008] Another aspect of the invention provides a coated roof
sheeting material comprising a sheet metal substrate, and a coating
covering at least a portion of the sheet metal substrate, wherein
the coating consists essentially of a cured latex resin, and
wherein the coated roof sheeting material has a solar reflectance
of at least 65 percent, a thermal emittance of at least 40 percent,
and a corrosion resistance of at least 500 h with no corrosion
spots when subjected to an ASTMB117 salt spray test.
[0009] A further aspect of the invention provides a method of
coating a sheet metal substrate comprising applying a coating
composition comprising a latex resin that is substantially free of
reflective pigments to the sheet metal substrate at a wet film
thickness of at least 1 micron, and curing the coating composition
to produce a coated metal sheet having a solar reflective index of
at least 65 and a corrosion resistance of at least 500 h with no
corrosion spots when subjected to an ASTMB117 salt spray test.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a partially schematic side view of a coated roof
sheeting material in accordance with an embodiment of the present
invention, illustrating solar reflectance and thermal emittance
properties.
[0011] FIG. 2 is a partially schematic side view illustrating a
method of coating and coiling metal sheets in rolling mill,
including the use of a roll coater for applying a coating
composition to the sheets in accordance with an embodiment of the
present invention.
[0012] FIG. 3 is a graph of total solar reflectance (TSR) vs. dry
film thickness (DFT) for coated metal sheets in accordance with
embodiments of the present invention.
[0013] FIG. 4 is a graph of thermal emittance (TE) vs. DFT for
coated metal sheets in accordance with embodiments of the present
invention.
[0014] FIG. 5 is a graph of solar reflective index (SRI) vs. DFT
for coated metal sheets in accordance with embodiments of the
present invention.
[0015] FIG. 6 is a graph of TSR vs. DFT for coated metal sheets in
accordance with embodiments of the present invention.
[0016] FIG. 7 is a graph of TE vs. DFT for coated metal sheets in
accordance with embodiments of the present invention.
[0017] FIG. 8 is a graph of SRI vs. DFT for coated metal sheets in
accordance with embodiments of the present invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0018] FIG. 1 schematically illustrates a coated sheet material 10
in accordance with an embodiment of the present invention including
a substrate sheet 12 and a coating layer 14. In certain
embodiments, the coated sheet 10 may be used in architectural
applications, such as roof sheeting material for a building 16 or
other structure. The coating 14 has a dry film thickness T
typically greater than 1 micron, for example, greater than 2 or 3
microns. In certain embodiments, the dry film thickness T of the
coating 14 may be from 3 to 10 or 20 microns. The substrate sheet
12 may be of any desired thickness, such as from 0.5 to 3 mm. For
example, the thickness of galvanized steel roof sheeting materials
may range from 0.5 to 2 mm in certain embodiments. Although the
sheet 12 shown in FIG. 1 is flat, any other shape may be provided,
such as corrugated, ribbed, and the like.
[0019] As illustrated in FIG. 1, a portion of solar radiation
incident on the coated sheet 10 is reflected from its surface with
a total solar reflectance TSR value. As used herein, the term
"total solar reflectance" means a measure of the ability of a
surface material to reflect sunlight--including the visible,
infrared, and ultraviolet wavelengths--on a scale of 0% to 100%. In
certain embodiments, the total solar reflectance TSR of the coated
sheet 10 is at least 60%, for example, at least 62% or 65%.
[0020] As further illustrated in FIG. 1, the coated sheet 10 has
thermal emittance TE properties. As used herein, the term "thermal
emittance" refers to the ability of a material to release absorbed
heat. A number between 0 and 1, or 0% and 100%, is used to express
emittance. In certain embodiments, the thermal emittance TE of the
coated sheet 10 is at least 0.3 (30%), for example, at least 0.4
(40%) or 0.5 (50%).
[0021] The total solar reflectance TSR and emittance TE properties,
as schematically illustrated in FIG. 1, may be combined to yield a
solar reflective index ("SRI"). As used herein, the term "solar
reflective index" is a value that incorporates both solar
reflectance and emittance in a single value to represent a
material's temperature in the sun. SRI quantifies how hot a surface
would get relative to standard black and standard white surfaces.
It is calculated using equations based on previously measured
values of solar reflectance and emittance as laid out in the
American Society for Testing and Materials Standard E 1980. In
accordance with ASTM Standard E 1980, values of TSR and TE are
input into a standard equation to calculate the SRI value. In
certain embodiments, the solar reflective index SRI is at least 65,
for example, at least 70 or 75.
[0022] In accordance with embodiments of the invention, the coating
composition comprises a latex resin. The latex resin may, or may
not, be self-crosslinking. The latex resin typically comprises from
20 to 60 weight percent of the coating composition, for example,
from about 30 to about 50 weight percent. In certain embodiments,
suitable monomers used for preparing the latex resins may include
vinyl aromatic monomers such as styrene, cycloaliphatic monomers
such as cyclohexyl methacrylate, and long-chain aliphatic monomers
such as 2-ethylhexyl acrylate, MMA and/or 2-ethylhexyl
methacrylate. Other types of monomers include cyclohexene,
2-ethyl-1-hexene, cyclohexanol, alpha-methylstyrene,
2-ethylhexanol, 2-ethylhexyl acetate, methyl-4-phenyl butyrate,
methyl myristate and/or methyl palmitate.
[0023] In certain embodiments, the monomers used in the latex resin
comprise a vinyl aromatic compound, such as a vinyl aromatic
monomer, which, in certain embodiments, comprises a compound that
has a calculated Tg of least 100.degree. C. Specific examples of
vinyl aromatic compounds are styrene (which has a calculated Tg of
100.degree. C.), .alpha.-methylstyrene (which has a calculated Tg
of 168.degree. C.), vinyltoluene, p-methylstyrene,
ethylvinylbenzene, vinylnaphthalene, vinylxylenes,
.alpha.-methylstyrene dimer (meth)acrylate, penta fluoro styrene,
and the like. In certain embodiments, styrene or another vinyl
aromatic monomer may comprise the most predominant monomer of the
resin on a weight percent basis.
[0024] In certain embodiments, the monomers of the latex resin
include cycloaliphatic(meth)acrylate monomers, such as
trimethylcyclohexyl acrylate, t-butyl cyclohexyl acrylate,
dicyclopentadiene(meth)acrylate, trimethylcyclohexyl methacrylate
(calculated Tg of 98.degree. C.), cyclohexyl methacrylate
(calculated Tg of 83.degree. C.), isobornyl methacrylate
(calculated Tg of 110.degree. C.), 2-ethylhexyl methacrylate,
tetrahydrofurfuryl methacrylate, 3,3,5-trimethylcyclohexyl
methacrylate (calculated Tg of 125.degree. C.), and/or
4-t-butylcyclohexyl methacylate, and the like.
[0025] In certain embodiments, the monomers of the latex resin
include an alkyl(meth)acrylate, which, in certain embodiments,
comprises a compound that has a calculated Tg of least 100.degree.
C. Specific examples of alkyl(meth)acrylates are C.sub.1-C.sup.24
alkyl(meth)acrylates, such as methyl(meth)acrylate (which has a
calculated Tg of 105.degree. C.), propyl(meth)acrylate,
butyl(meth)acrylate, isobutyl(meth)acrylate, hexyl(meth)acrylate,
2-ethylhexyl(meth)acrylate, octyl(meth)acrylate,
decyl(meth)acrylate, dodecyl(meth)acrylate,
pentadecyl(meth)acrylate, hexadecyl(meth)acrylate,
octadecyl(meth)acrylate, and nonadecyl(meth)acrylate, and mixtures
thereof. Other monomers include, for example, nitriles, such as
acrylonitrile and/or methacrylonitrile.
[0026] Some non-limiting examples of latex resins that may be used
in the coating compositions of the present invention are
commercially available from Nuplex, Lubrizol, Rohm and Haas,
Alberdingk Boley Company, Omnova and DSM Neoresins, such as Joncryl
1982, Caroboset CR-781, Alberdingk AC 2403, Alberdingk 2360,
Neocryl XK-98 and the like.
[0027] The latex resin may have an average particle size of from 50
nm to 300 nm, for example from 60 nm to 100 or 150 nm; a glass
transition temperature (T.sub.G) of from -20 to 100.degree. C.,
typically from zero to 20 or 50.degree. C.; and an acid number of
from 0 to 20, typically from 2 to 10.
[0028] The coating compositions of the present invention may be
waterborne. In certain embodiments, water may comprise from 20 to
80 weight percent of the coating compositions, for example, from 50
to 65 weight percent. In certain embodiments, the coating
compositions comprise less than 10 weight percent organic solvents,
for example, less than 7 or 4 weight percent, based on the total
weight of the composition. The resin solids content of the coating
compositions may be relatively high, for example, greater than 35
or 40 weight percent, based on the total weight of the
composition.
[0029] The coating compositions may have little or no volatile
organic content (VOC). For example, the coating compositions may
comprise less than 1.5 weight percent VOCs, for example, less than
1 or 0.5 weight percent VOCs, based on the total weight of the
composition. In certain embodiments, the coating compositions are
substantially free of VOCs.
[0030] The coating compositions may further comprise at least one
coalescing agent in an amount of up to 10 weight percent, for
example, in an amount of from 2 to 3 weight percent, based on the
total weight of the coating composition. Examples of suitable
coalescing agents include butyl carbitol commercially available
from Dow Chemical Company, Dowanol DPM, Dowanol DPnB, Dowanol PPh,
butyl cellosolve or Dowanol DPnP. In accordance with embodiments of
the present invention, the coalescing agents form a thin film
around the latex resin particles, which helps them coalesce.
Improved coalescence of the latex resin particles results in very
fine particle sizes and a uniform microstructure, which provides
improved corrosion protection in comparison with other types of
coatings having larger resin particle sizes. For example, in
accordance with certain embodiments of the present invention, the
average resin particle size may be less than 150 nanometers, for
example, less than 100 or 80 nanometers.
[0031] In certain embodiments, wax may be added to the coating
compositions in amounts up to 10 weight percent, for example, from
0.5 to 3 weight percent, based on the total weight of the coating
composition. Suitable types of wax include Ceraflour 913, Worleeadd
352, Aquamat 272, Aquamat 270, Aquacer 539, and combinations
thereof. For example, wax sold under the designation Aquamat 272 by
BYK Chemie may be used. The type and amount of wax may be
controlled in order to improve scratch resistance of the coated
sheet materials. For example, when the coated sheets are formed
into coils, the use of wax additives may reduce or prevent
scratching during the coiling an uncoiling processes, as well as
during subsequent installation and use of the coated sheet
materials. In certain embodiments, the amount of wax added to the
coating composition is limited in order to avoid unwanted slippage
when the coated sheets are coiled, e.g., to prevent unwanted
"telescoping" of the coils due to low friction between the adjacent
coil layers.
[0032] Various other additives may optionally be added to the
coating compositions in accordance with certain embodiments of the
invention. For example, suitable additives include thickeners,
defoamers, surfactants, rust inhibitors, pH control agents, silica,
and tints.
[0033] Suitable thickeners include Acrysol ASE-60, Aquatix 8421,
DSX-1550, and Laponite RD. When used, such thickening agents may be
present in amounts up to 7 weight percent, for example, from 0.5 to
4 weight percent, based on the total weight of the coating
composition.
[0034] Suitable defoamers include BYK-011, BYK-20, BYK-32, BYK 34
and Drewplus L-419 available from Ashland in amounts up to 2 weight
percent, for example, from 0.1 to 0.5 weight percent, based on the
total weight of the coating composition.
[0035] Suitable surfactants include Zonyl FSP available from
DuPont, Surfynol 104E available from Air Products, BYK 346, and
BYK348 in amounts up to 2 weight percent, for example, from 0.1 to
0.5 weight percent, based on the total weight of the coating
composition.
[0036] Suitable rust inhibitors include Halox 550, Halox Flash
X-150, 330, Halox SZP-391, ammonium benzoate, and sodium nitrite in
typical amounts up to 1 weight percent, for example, from 0.4 to
0.6 weight percent, based on the total weight of the coating
composition.
[0037] In certain embodiments, the coating compositions are
substantially free of certain metal salts such as metal phosphates,
phosphocarbonates and phosphosilicates. For example, the
compositions may be substantially free of zinc phosphate, calcium
phosphate, calcium phosphosilicate and/or calcium-enriched
silica.
[0038] Suitable pH control agents include any water soluble amine
such as dimethylethanol amine (DMEA) available from Avecia in
typical amounts up to 1 weight percent, for example, from 0.01 to
0.2 weight percent, based on the total weight of the coating
composition.
[0039] In accordance with certain embodiments of the invention, the
coatings are substantially free of chrome. In such embodiments,
chrome is not purposely added to the coating compositions and is
only present in trace levels or as an impurity.
[0040] In certain embodiments, chromate-containing materials may be
added to the coating compositions. Such chromate-containing coating
compositions may be particularly useful as primer coatings. For
example, strontium chromate may be added in amounts up to 12 weight
percent, for example, from 0.2 to 1 weight percent, based on the
total weight of the coating composition. Such strontium
chromate-containing additives may provide improved corrosion
resistance properties. When used as primer coatings, the coating
compositions may further include colorants and tints typically used
in primers, such as titanium dioxide and the like.
[0041] In certain embodiments, silica may be added to the coating
compositions, for example, in amounts from 0.1 to 2 or 3 weight
percent or more. Some examples of silica include Lo-Vel 275 silica
from PPG Industries and Aerosil 200 silica from Air Products.
[0042] In certain embodiments, the coating compositions and cured
coatings are substantially free of reflective pigments. As used
herein, the term "reflective pigment" means plate-like or
sheet-like interference pigments such as mica, silicates, silicon
dioxide and aluminum oxide. Solarflair 9870 from Eckart is an
example of a reflective pigment. As used herein, the term
"substantially free of reflective pigments" means that the coatings
have zero or minimal amounts of reflective pigments while achieving
the desired level of solar reflectance and/or solar reflective
index. For example, the cured coatings may have less than 2 or 1
weight percent reflective pigment. Although the coatings may be
substantially free of reflective pigments, they still maintain
sufficient solar reflectance properties and solar reflective index
values, e.g., SRIs of 65 or greater. The cost of reflective pigment
additives may thus be avoided, while still providing a desired
level of solar reflectance.
[0043] In certain embodiments, at least one colored pigment or tint
may be added to the coating compositions. Colored pigments and
tints are different from reflective interference pigments and
include standard inorganic and organic pigments, such as those
found in conventional paints and primers. For example, various
colored pigments are listed in the Dry Color Manufacturers
Association (DCMA) classifications. Such colored pigments and tints
typically comprise particles having substantially equiaxed
morphologies, e.g., aspect ratios of about 1:1, in comparison with
plate-like and sheet-like reflective interference pigments having
relatively high aspect ratios. One suitable type of colored pigment
includes TiO.sub.2 in an amount up to 35 weight percent, for
example, from 1 to 25 weight percent, based on the total weight of
the coating composition. Aquext white tint commercially available
from PPG Industries and Corrosperse 176E chrome tint commercially
available from Wayne Pigments are examples of suitable tints.
[0044] In certain embodiments, the coating is substantially free of
colored pigments and tints. For example, the coatings may be
substantially clear and colorless.
[0045] In certain embodiments, conductive particles such as
graphenic carbon particles may be added to the coating compositions
in amounts of to 5 weight percent, for example, from 1 to 2 weight
percent, based on the total weight of the coating composition. Such
graphenic carbon particles may provide improved thermal emissivity
properties. The graphenic carbon particles may be obtained from
commercial sources, or may be made in accordance with the methods
and apparatus described in U.S. application Ser. Nos. 13/249,315
and 13/309,894, which are incorporated herein by reference.
Exemplary commercially available graphenic carbon particles are
available from Angstron and XG Sciences.
[0046] As used herein, the term "graphenic carbon particles" means
carbon particles having structures comprising one or more layers of
one-atom-thick planar sheets of sp.sup.2-bonded carbon atoms that
are densely packed in a honeycomb crystal lattice. The average
number of stacked layers may be less than 100, for example, less
than 50. In certain embodiments, the average number of stacked
layers is 30 or less, such as 20 or less, 10 or less, or, in some
cases, 5 or less. The graphenic carbon particles may be
substantially flat, however, at least a portion of the planar
sheets may be substantially curved, curled, creased or buckled. The
particles typically do not have a spheroidal or equiaxed
morphology.
[0047] In certain embodiments, the graphenic carbon particles
present in the compositions of the present invention have a
thickness, measured in a direction perpendicular to the carbon atom
layers, of no more than 10 nanometers, no more than 5 nanometers,
or, in certain embodiments, no more than 4 or 3 or 2 or 1
nanometers, such as no more than 3.6 nanometers. In certain
embodiments, the graphenic carbon particles may be from 1 atom
layer up to 3, 6, 9, 12, 20 or 30 atom layers thick, or more. In
certain embodiments, the graphenic carbon particles present in the
compositions of the present invention have a width and length,
measured in a direction parallel to the carbon atoms layers, of at
least 50 nanometers, such as more than 100 nanometers, in some
cases more than 100 nanometers up to 500 nanometers, or more than
100 nanometers up to 200 nanometers. The graphenic carbon particles
may be provided in the form of ultrathin flakes, platelets or
sheets having relatively high aspect ratios (aspect ratio being
defined as the ratio of the longest dimension of a particle to the
shortest dimension of the particle) of greater than 3:1, such as
greater than 10:1.
[0048] In certain embodiments, the graphenic carbon particles used
in the compositions of the present invention have relatively low
oxygen content. For example, the graphenic carbon particles used in
certain embodiments of the compositions of the present invention
may, even when having a thickness of no more than 5 or no more than
2 nanometers, have an oxygen content of no more than 2 atomic
weight percent, such as no more than 1.5 or 1 atomic weight
percent, or no more than 0.6 atomic weight, such as about 0.5
atomic weight percent. The oxygen content of the graphenic carbon
particles can be determined using X-ray Photoelectron Spectroscopy,
such as is described in D. R. Dreyer et al., Chem. Soc. Rev. 39,
228-240 (2010).
[0049] In certain embodiments, the graphenic carbon particles used
in the compositions of the present invention have a B.E.T. specific
surface area of at least 50 square meters per gram, such as 70 to
1000 square meters per gram, or, in some cases, 200 to 1000 square
meters per grams or 200 to 400 square meters per gram. As used
herein, the term "B.E.T. specific surface area" refers to a
specific surface area determined by nitrogen adsorption according
to the ASTMD 3663-78 standard based on the Brunauer-Emmett-Teller
method described in the periodical "The Journal of the American
Chemical Society", 60, 309 (1938).
[0050] In certain embodiments, the graphenic carbon particles used
in the compositions of the present invention have a Raman
spectroscopy 2D/G peak ratio of at least 1.1, for example, at least
1.2 or 1.3. As used herein, the term "2D/G peak ratio" refers to
the ratio of the intensity of the 2D peak at 2692 cm.sup.-1 to the
intensity of the G peak at 1,580 cm.sup.-1.
[0051] In certain embodiments, the graphenic carbon particles used
in the compositions of the present invention have a relatively low
bulk density. For example, the graphenic carbon particles used in
certain embodiments of the present invention are characterized by
having a bulk density (tap density) of less than 0.2 g/cm.sup.3,
such as no more than 0.1 g/cm.sup.3. For the purposes of the
present invention, the bulk density of the graphenic carbon
particles is determined by placing 0.4 grams of the graphenic
carbon particles in a glass measuring cylinder having a readable
scale. The cylinder is raised approximately one-inch and tapped 100
times, by striking the base of the cylinder onto a hard surface, to
allow the graphenic carbon particles to settle within the cylinder.
The volume of the particles is then measured, and the bulk density
is calculated by dividing 0.4 grams by the measured volume, wherein
the bulk density is expressed in terms of g/cm.sup.3.
[0052] In certain embodiments, the graphenic carbon particles used
in the compositions of the present invention have a compressed
density and a percent densification that is less than the
compressed density and percent densification of graphite powder and
certain types of substantially flat graphenic carbon particles.
Lower compressed density and lower percent densification are each
currently believed to contribute to better dispersion and/or
rheological properties than graphenic carbon particles exhibiting
higher compressed density and higher percent densification. In
certain embodiments, the compressed density of the graphenic carbon
particles is 0.9 or less, such as less than 0.8, less than 0.7,
such as from 0.6 to 0.7. In certain embodiments, the percent
densification of the graphenic carbon particles is less than 40%,
such as less than 30%, such as from 25 to 30%.
[0053] For purposes of the present invention, the compressed
density of graphenic carbon particles is calculated from a measured
thickness of a given mass of the particles after compression.
Specifically, the measured thickness is determined by subjecting
0.1 grams of the graphenic carbon particles to cold press under
15,000 pound of force in a 1.3 centimeter die for 45 minutes,
wherein the contact pressure is 500 MPa. The compressed density of
the graphenic carbon particles is then calculated from this
measured thickness according to the following equation:
Compressed Density ( g / cm 3 ) = 0.1 grams .PI. * ( 1.3 cm / 2 ) 2
* ( measued thickness in cm ) ##EQU00001##
[0054] The percent densification of the graphenic carbon particles
is then determined as the ratio of the calculated compressed
density of the graphenic carbon particles, as determined above, to
2.2 g/cm.sup.3, which is the density of graphite.
[0055] In certain embodiments, the graphenic carbon particles have
a measured bulk liquid conductivity of at least 100 microSiemens,
such as at least 120 microSiemens, such as at least 140
microSiemens immediately after mixing and at later points in time,
such as at 10 minutes, or 20 minutes, or 30 minutes, or 40 minutes.
For the purposes of the present invention, the bulk liquid
conductivity of the graphenic carbon particles is determined as
follows. First, a sample comprising a 0.5% solution of graphenic
carbon particles in butyl cellosolve is sonicated for 30 minutes
with a bath sonicator. Immediately following sonication, the sample
is placed in a standard calibrated electrolytic conductivity cell
(K=1). A Fisher Scientific AB 30 conductivity meter is introduced
to the sample to measure the conductivity of the sample. The
conductivity is plotted over the course of about 40 minutes.
[0056] In accordance with certain embodiments, percolation, defined
as long range interconnectivity, occurs between the conductive
graphenic carbon particles. Such percolation may reduce the
resistivity of the coating compositions. The conductive graphenic
particles may occupy a minimum volume within the coating such that
the particles form a continuous, or nearly continuous, network. In
such a case, the aspect ratios of the graphenic carbon particles
may affect the minimum volume required for percolation.
Furthermore, the surface energy of the graphenic carbon particles
may be the same or similar to the surface energy of the elastomeric
rubber. Otherwise, the particles may tend to flocculate or demix as
they are processed.
[0057] The graphenic carbon particles utilized in the compositions
of the present invention can be made, for example, by thermal
processes. In accordance with embodiments of the invention, the
graphenic carbon particles are produced from carbon-containing
precursor materials that are heated to high temperatures in a
thermal zone. For example, the graphenic carbon particles may be
produced by the systems and methods disclosed in U.S. patent
application Ser. Nos. 13/249,315 and 13/309,894.
[0058] In certain embodiments, the graphenic carbon particles may
be made by using the apparatus and method described in U.S. patent
application Ser. No. 13/249,315 at [0022] to [0048] in which (i)
one or more hydrocarbon precursor materials capable of forming a
two-carbon fragment species (such as n-propanol, ethane, ethylene,
acetylene, vinyl chloride, 1,2-dichloroethane, allyl alcohol,
propionaldehyde, and/or vinyl bromide) is introduced into a thermal
zone (such as a plasma); and (ii) the hydrocarbon is heated in the
thermal zone to a temperature of at least 1,000.degree. C. to form
the graphenic carbon particles. In other embodiments, the graphenic
carbon particles may be made by using the apparatus and method
described in U.S. patent application Ser. No. 13/309,894 at [0015]
to [0042] in which (i) a methane precursor material (such as a
material comprising at least 50 percent methane, or, in some cases,
gaseous or liquid methane of at least 95 or 99 percent purity or
higher) is introduced into a thermal zone (such as a plasma); and
(ii) the methane precursor is heated in the thermal zone to form
the graphenic carbon particles. Such methods can produce graphenic
carbon particles having at least some, in some cases all, of the
characteristics described above.
[0059] During production of the graphenic carbon particles by the
methods described above, a carbon-containing precursor is provided
as a feed material that may be contacted with an inert carrier gas.
The carbon-containing precursor material may be heated in a thermal
zone, for example, by a plasma system. In certain embodiments, the
precursor material is heated to a temperature ranging from
1,000.degree. C. to 20,000.degree. C., such as 1,200.degree. C. to
10,000.degree. C. For example, the temperature of the thermal zone
may range from 1,500 to 8,000.degree. C., such as from 2,000 to
5,000.degree. C. Although the thermal zone may be generated by a
plasma system, it is to be understood that any other suitable
heating system may be used to create the thermal zone, such as
various types of furnaces including electrically heated tube
furnaces and the like.
[0060] The gaseous stream may be contacted with one or more quench
streams that are injected into the plasma chamber through at least
one quench stream injection port. The quench stream may cool the
gaseous stream to facilitate the formation or control the particle
size or morphology of the graphenic carbon particles. In certain
embodiments of the invention, after contacting the gaseous product
stream with the quench streams, the ultrafine particles may be
passed through a converging member. After the graphenic carbon
particles exit the plasma system, they may be collected. Any
suitable means may be used to separate the graphenic carbon
particles from the gas flow, such as, for example, a bag filter,
cyclone separator or deposition on a substrate.
[0061] Without being bound by any theory, it is currently believed
that the foregoing methods of manufacturing graphenic carbon
particles are particularly suitable for producing graphenic carbon
particles having relatively low thickness and relatively high
aspect ratio in combination with relatively low oxygen content, as
described above. Moreover, such methods are currently believed to
produce a substantial amount of graphenic carbon particles having a
substantially curved, curled, creased or buckled morphology
(referred to herein as a "3D" morphology), as opposed to producing
predominantly particles having a substantially two-dimensional (or
flat) morphology. This characteristic is believed to be reflected
in the previously described compressed density characteristics and
is believed to be beneficial in the present invention because, it
is currently believed, when a significant portion of the graphenic
carbon particles have a 3D morphology, "edge to edge" and
"edge-to-face" contact between graphenic carbon particles within
the composition may be promoted. This is thought to be because
particles having a 3D morphology are less likely to be aggregated
in the composition (due to lower Van der Waals forces) than
particles having a two-dimensional morphology. Moreover, it is
currently believed that even in the case of "face to face" contact
between the particles having a 3D morphology, since the particles
may have more than one facial plane, the entire particle surface is
not engaged in a single "face to face" interaction with another
single particle, but instead can participate in interactions with
other particles, including other "face to face" interactions, in
other planes. As a result, graphenic carbon particles having a 3D
morphology are currently thought to provide the best conductive
pathway in the present compositions and are currently thought to be
useful for obtaining electrical conductivity characteristics sought
by the present invention, particularly when the graphenic carbon
particles are present in the composition in relatively low
amounts.
[0062] FIG. 2 schematically illustrates a roll coating method for
applying coating compositions onto sheet materials in accordance
with an embodiment of the present invention. In the embodiment
shown, the coating operation may be conducted in a conventional
rolling mill. Metal sheet material, such as galvanized steel or the
like, is provided in a long strip 5 that passes under
oppositely-rotating coating rollers 20 and 22, which are fed with a
supply of a coating composition 24. The uncoated strip 5 passes
under the coating rollers 20 and 22, where a layer of the coating
composition 24 is deposited on the upper surface of the sheet
material. The coated sheet material 10 may be formed into a coil 26
for storage and transportation for use in various applications,
such as galvanized steel roof sheeting.
[0063] During the roll coating process, the coating composition is
typically applied to the sheet material 5 with a wet film thickness
of at least 1 micron, typically at least 1 or 5 microns. In certain
embodiments, the wet film thickness of the coating material is from
5 to 15 or 20 microns. In certain embodiments, the deposition rate
of the coating composition may be at least 200 ft/min, typically at
least 300 ft/min or 350 ft/min.
[0064] After application, the coating compositions typically dry
and cure quickly with minimal VOC emissions. Curing times are
typically in less than 1 minute, for example, less than 10 or 5
seconds. Typical curing temperatures are below 300.degree. F., for
example, below 275.degree. or 250.degree. F. In certain
embodiments, curing times may be less than 3 or 2 seconds at
temperatures of 225.degree. F. or 200.degree. F., or less.
[0065] The dry film thickness of the cured coating is typically at
least 1 micron up to 15 or 20 microns. For example, the dry film
thickness may be from 5 to 10 microns. In accordance with the
present invention, such relatively thin coating layers have been
found to significantly increase the solar reflective index of metal
roof sheeting materials.
[0066] The following examples illustrate various aspects of the
present invention, but are not intended to limit the scope of the
invention.
Examples
[0067] Coating compositions were prepared and tested as described
in Tables 1-4 below.
TABLE-US-00001 TABLE 1 Coating Composition Nos. 1-3 Sample Sample
Sample Components No. 1 No. 2 No. 3 Acrylic Latex Resin 198.10
199.18 165.41 Deionized Water 15.23 17.84 85.30 Defoamer 0.48 0.48
0.51 Surfynol Surfactant 1.04 1.04 1.06 Surfactant 1.04 1.04 1.06
Coalescing Agent 10.01 10.01 10.15 Chrome Tint 5.98 -- 5.98 White
Tint -- -- 154.63 Rust Inhibitor 2.41 2.43 2.46 Thickener 3.55 3.55
5.36 Deionized Water 3.55 3.55 0.54 pH Control Agent 0.53 0.53 0.54
Deionized Water 0.53 0.53 0.54 Wax 3.64 3.64 10.52 Total Weight in
Grams 246.09 243.82 444.06
TABLE-US-00002 TABLE 2 Coating Composition No. 4 Components Sample
No. 4 Latex Resin 201.14 UC Intermediate.sup.1 22.27 Deionized
Water 3.70 Defoamer 0.13 Rust Inhibitor Pigment 8.05 Surfactant
0.24 Silica 1.08 Deionized Water 0.10 Total Weight in Grams 236.62
.sup.1Acrylic Emulsion Joncryl 538 (98.88); Defoamer (0.74);
Deionized Water (5.0); Silica (25.11); Corrosion Pigment (49.78);
Reflective Pigment (25.11); and Defoamer (0.26).
[0068] The components listed in Tables 1 and 2 above were added
together in the order described in each table under gentle
stirring. The coating compositions were allowed to equilibrate
overnight before panel preparation. Viscosity and pH were checked
the next day. The coating compositions were applied to galvanized
steel substrates using a wire drawdown bar. The coated panels were
placed in a conveyor oven set at a temperature to obtain a peak
metal temperature of 190.degree. F. in two seconds dwell time (line
speed). The coated panels were tested, with the results shown in
Table 3 below.
TABLE-US-00003 TABLE 3 Test Results Sample Sample Sample Sample No.
1 No. 2 No. 3 No. 4 % Weight 41.82 41.62 45.0 44.03 Solids
Viscosity 10-15 10-15 12-20 9-25 (Seconds) (measured using #4 Zahn
Cup at room temperature) Dry Film 0.15-0.20 0.15-0.20 0.4-0.5
0.15-0.25 Thickness (mils) (mils) (mils) (mils) 3.8-5.1 3.8-5.1
10.2-12.7 3.8-6.4 (microns) (microns) (microns) (microns) Pencil
HB-F HB-F HB-F B Hardness T-Bend 1/3 np/nc 1/3 np/nc 1/3 np/nc 1/3
np/nc Reverse Pass Pass Pass Pass Impact X-Hatch Pass Pass Pass
Pass Adhesion Butler No Corrosion No Corrosion No Corrosion
Corrosion - fail Immersion Salt Spray No Black No Black No Black
Corrosion - fail Spots Spots Spots Wet Stack No Pressure No
Pressure No Pressure Pressure Mottling Mottling Mottling mottling,
black spots TSR (%) 66.8 65 70.7 66.8 TE (%) 54 58 78 54 SRI 71 69
84 71
[0069] In accordance with the pencil hardness test, ASTM D3363, a
pencil is held firmly against the coating at a 45 degree angle and
pushed away from the operator in a 0.25 inch stroke. Sufficient
pressure is exerted downward and forward either to cut or scratch
the film. The process is repeated down the hardness scale until a
pencil is found that will not cut through the film to the
substrate. The scale of hardness is: 6B (very soft) up to a 6H
(very hard).
[0070] In accordance with the Butler immersion test, ASTM D870,
panels with cut edges are placed in a cup of covered tap water, and
placed in a humidity cabinet 100 F/100% humidity, for 1000 hours.
The panels are then removed from the water, and visually evaluated
for any red or white rust, black spots and or blisters on the faces
and edges of the panels.
[0071] In accordance with the salt spray test, ASTM B117, panels
are placed with taped cut edges in a 95 F/5% NaCl solution cabinet
for 1000 hours. The panels are then removed from the cabinet and
visually evaluated for any red or white rust, black spots and
blister defects on the faces of the panels.
[0072] In accordance with the wet stack test, ASTM D7376-10A,
panels are sprayed with DI-water, stacked face to face, and clipped
together in a bundle to simulate a wound coil. The bundles are
placed in a 100 F/100% humidity cabinet for 1000 hours. The bundles
are then removed and visually evaluated for dark stains or white
stains (pressure mottling).
[0073] Galvanized steel panels coated with compositions similar to
Sample Nos. 1 and 2 described above were tested for TSR, TE and SRI
properties at various dry film thicknesses (DFT). The results are
shown in the plots of FIGS. 3, 4 and 5.
[0074] Galvanized steel panels coated with compositions similar to
Sample Nos. 1 and 2 described above, but with additions of
interference pigment available from Eckart under the designation
SolarFlair in an amount of 5 weight percent based on the total
weight of the coating composition, were tested for TSR, TE and SRI
properties at various dry film thicknesses (DFT). The results are
shown in the plots of FIGS. 6, 7 and 8.
[0075] Different types of graphenic carbon were added in an amount
of 1 weight percent to coating compositions similar to Sample No. 1
above. Sample No. 5 included graphenic carbon particles produced in
accordance with U.S. patent application Ser. No. 13/309,894. Sample
No. 6 included commercially available graphenic carbon particles
from Angstron sold under the designation N-006-010-P. Sample No. 7
included commercially available graphenic carbon particles from XG
Sciences sold under the designation X-GNP-M-25. Panels were
prepared by drawdown on a galvanized steel substrate at a film
thickness of 5 microns. The panels were then cured at peak metal
temperature of 190.degree. F. for 2 seconds using a conveyer oven.
The panels were tested, with the results shown below in Table
4.
TABLE-US-00004 TABLE 4 Test Results Sample % Graphene Diameter
Thickness Salt Spray - No. Graphene Type (microns) (nm) SRV TE SRI
1000 h 1 0% NA NA NA 66.3 0.55 70 Excellent 5 1% Graphenic 59.7
0.54 59 very few Carbon blisters Particles 6 1% Commercially <14
10-20 42.2 0.72 41 Excellent available N-006-010-P graphenic carbon
7 1% Commercially 25 6 59.5 0.56 60 dense available blisters
X-GNP-M-25 graphenic carbon
[0076] For purposes of this detailed description, it is to be
understood that the invention may assume various alternative
variations and step sequences, except where expressly specified to
the contrary. Moreover, other than in any operating examples, or
where otherwise indicated, all numbers expressing, for example,
quantities of ingredients used in the specification and claims are
to be understood as being modified in all instances by the term
"about". Accordingly, unless indicated to the contrary, the
numerical parameters set forth in the following specification and
attached claims are approximations that may vary depending upon the
desired properties to be obtained by the present invention. At the
very least, and not as an attempt to limit the application of the
doctrine of equivalents to the scope of the claims, each numerical
parameter should at least be construed in light of the number of
reported significant digits and by applying ordinary rounding
techniques.
[0077] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the invention are approximations,
the numerical values set forth in the specific examples are
reported as precisely as possible. Any numerical value, however,
inherently contains certain errors necessarily resulting from the
standard variation found in their respective testing
measurements.
[0078] Also, it should be understood that any numerical range
recited herein is intended to include all sub-ranges subsumed
therein. For example, a range of "1 to 10" is intended to include
all sub-ranges between (and including) the recited minimum value of
1 and the recited maximum value of 10, that is, having a minimum
value equal to or greater than 1 and a maximum value of equal to or
less than 10.
[0079] In this application, the use of the singular includes the
plural and plural encompasses singular, unless specifically stated
otherwise. In addition, in this application, the use of "or" means
"and/or" unless specifically stated otherwise, even though "and/or"
may be explicitly used in certain instances.
[0080] It will be readily appreciated by those skilled in the art
that modifications may be made to the invention without departing
from the concepts disclosed in the foregoing description. Such
modifications are to be considered as included within the following
claims unless the claims, by their language, expressly state
otherwise. Accordingly, the particular embodiments described in
detail herein are illustrative only and are not limiting to the
scope of the invention which is to be given the full breadth of the
appended claims and any and all equivalents thereof.
* * * * *