Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02581032 2013-08-08
SOLAR HEAT REFLECTIVE ROOFING MEMBRANE
AND PROCESS FOR MAKING THE SAME
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates to bituminous roofing products such as asphalt-
based roofing membranes and processes for making such roofing products.
2. Brief Description of the Prior Art.
Asphalt-based roofing membranes are excellent waterproofing materials that
have been extensively used in low-slope roofing systems to provide long-
lasting and
satisfactory roof coverings. Low-slope roofing systems are extensively used
for
commercial and industrial buildings. Examples of low-slope roofing systems are
built-
up roofs (BUR), modified bitumen roofs, and single-ply or membrane roofing
systems.
Asphalt-based roofing membranes are frequently used as waterproofing
underlayment
in low-rise roofing systems, as well as the uppermost or finish layer in built-
up-roofs.
Built-up roofs are sometimes covered with a layer of gravel or granular
mineral
material to protect the roofing membrane against mechanical damage.
Mineral-surfaced asphalt shingles, such as those described in ASTM D225 or
D3462, are generally used for steep-sloped roofs to provide water-shedding
function while
adding aesthetically pleasing appearance to the roofs_ Conversely, roll goods
such as
asphalt-based roofing membranes are generally used for low-slope roofs.
Pigment-
coated mineral particles are commonly used as color granules in roofing
applications to
provide aesthetic as well as protective functions_ Roofing granules are
generally used
in asphalt shingles or in roofing membranes to protect asphalt from harmful
ultraviolet
radiation.
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Roofing products such as asphalt shingles and roll stock are typically
composite
articles including a non-woven glass fiber or felt web covered with a coating
of water
repellent bituminous material, and optionally surfaced with protective mineral-
based
roofing granules. The bituminous material is characteristically black in
color, and is
strongly absorptive of incident solar radiation. Thus, asphalt-based roofing
membranes
can absorb significant amounts of solar radiation, which can result in
elevated roof
temperatures. This can contribute to the increase of energy usage for indoor
air-
conditioning, especially in a hot climate.
Asphalt shingles are generally constructed from asphalt-saturated roofing
felts and
surfaced by pigmented color granules. Asphalt-based roofing membranes are
similarly
constructed; except that roofing granules are not frequently employed.
However, both
asphalt shingles and asphalt-based roofing membranes are known to have low
solar
reflectivity and hence will absorb solar heat especially through the near
infrared range of
the solar spectrum.
This phenomenon increases as the surface becomes dark in color. For example,
white-colored asphalt shingles with CIE L* greater than 60 can have solar
reflectance
greater than 25% (ASTM El 918 method), whereas non-white asphalt shingles with
L* less
than 60 can have solar reflectance in the range of 5-20%. As a result, it is
common to
measure temperatures as high as 71 ¨77 degrees C (160.- 170 degrees F) on the
surface of dark roofing shingles on a sunny day with 27 degree C (80 degrees
F) ambient
temperature.
Reduced energy consumption is an important national goal. For example, the
State of California has a code requirement that all commercial roofing
materials in low-
slope applications need to exceed a minimum of 70% solar reflectance in order
to
meet California's energy budget code. Also, in order to qualify as Energy Star
roofing
material, a roofing membrane needs to exceed 65% solar reflectance.
Typically, even a white mineral-surfaced, asphalt-based roofing membrane has
only 30-35% solar reflectance.
In order to address this problem, externally applied coatings have sometimes
been
applied directly onto the shingle or membrane surface on the roof. White
pigment-
containing latex coatings have been proposed. Similarly, aluminum-coated
asphalt roofing
membranes have been employed to achieve solar heat reflectivity. U.S. Patent
6,245,850
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discloses a reflective asphalt emulsion for producing a reflective asphalt
roofing
membrane.
The use of exterior-grade coatings colored by infrared-reflective pigments has
also
been proposed for spraying onto the roof in the field. U.S. Patent Application
Publication
No. 2003/0068469A1 discloses an asphalt-based roofing material comprising a
mat
saturated with asphalt coating and a top coating having a top surface layer
that has a solar
reflectance of at least 70%.
U.S. Patent Application Publication No. 2002/0160151A1 discloses an integrated
granule product comprising a film having a plurality of ceramic-coated
granules bonded to
the film by a cured adhesive and the cured adhesive or the film can have
pigments. Such
integrated granule product can be directly bonded to an asphalt-based
substrate as
roofing products.
In order to increase solar reflectance of built-up roofs, reflective coatings
have
been applied directly onto the surface of the roofing membrane. For example,
white
pigment containing latex coatings have been proposed and evaluated by various
manufacturers. In addition, white single-ply roofing membranes formed from
thermoplastic elastomers, PVC, or EPDM, etc., have been developed to achieve
the
required solar reflectance. Performance Roof Systems (Kansas City, MO) has
also
developed an asphalt-based roofing membrane having a white acrylic pre-
impregnated
mat on the top surface.
Laminated single-ply roofing membranes are known, such as those disclosed in
U.S. Patents 6,502,360; 5,456,785; 5,620,554; and 5,643,399. U.S. Patent
6,296,912
discloses a roofing membrane having a fibrous layer on top for providing a
secure
surface for roof installation personnel.
There is a continuing need for roofing materials that have improved resistance
to
thermal stresses while providing an attractive appearance. Further, there is a
continuing need to develop asphalt-based roofing membranes with solar
reflectance
greater than 70%.
SUMMARY OF THE INVENTION
The present invention provides a roofing membrane with high solar heat-
reflectance. The roofing membrane comprises a bituminous base sheet; a tie-
layer
comprising a reinforcement material; and a solar heat-reflective upper layer.
The solar
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heat-reflective upper layer preferably includes a first polymeric coating
comprising at
least one first polymeric binder and at least one first solar heat-reflective
pigment.
The first polymeric coating has a first polymeric binder that is preferably
selected
from the group consisting of acrylic copolymers, polyesters, polyamides,
epoxies,
nonacid-containing polyolefins, polyolefin alloys, polypropylene, acid-
containing
polyolefins, fluoropolymers, polyvinyl chloride, polyester block amide,
ethylene-
chlorotrifluorethylene, and polyvinylidene fluoride In a presently preferred
embodiment,
the polymeric binder is an acrylic copolymer. Preferably, the at least one
first solar heat
reflective pigment is titanium dioxide.
The solar heat-reflective upper layer can include both an inner sub-layer and
an
outer sub-layer. The inner sub-layer is preferably comprised of a second
polymeric
coating adapted to interpenetrate the tie-layer and at least one second solar
heat-
reflective pigment.
Preferably, the reinforcement material comprises a non-woven web of fibers.
Preferably, the nonwoven web comprises fibers selected from the group of glass
fibers,
polymeric fibers and combinations thereof.
The second polymeric coating can comprise a second polymeric binder is also
preferably selected from the group consisting of acrylic copolymers,
polyesters,
polyamides, epoxies, nonacid-containing polyolefins, polyolefin alloys,
polypropylene,
acid-containing polyolefins, polyvinyl chloride, fluoropolymers, polyester
block amide,
ethylene-chlorotrifluorethylene, and polyvinylidene fluoride. In a presently
preferred
embodiment, the polymeric binder is also an acrylic copolymer. Preferably, the
at least
one second solar heat reflective pigment is also titanium dioxide.
In one presently preferred embodiment of the present invention, the outer sub-
layer comprises a durable material. In this case, the outer sub-layer
comprises a
material selected from polyvinylidene fluoride, UV-curable coating
compositions, acrylic
based coating compositions, and silicone emulsions.
In one presently preferred embodiment of the present invention, the roofing
membrane is formed from a bituminous base sheet and an intermediate web
including
tie-layer and the solar heat-reflective layer. Preferably, the intermediate
web is formed
by coating the tie-layer with a solar heat-reflective coating material.
The present invention also provides a process for preparing a roofing membrane
with high solar heat reflectance. In one presently preferred embodiment, the
preparative
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process of the present invention comprises laminating a tie-layer to a
bituminous base
sheet to form an intermediate sheet; depositing a polymeric coating
composition on the
intermediate sheet; and curing or solidifying the coating composition.
Preferably, the
polymeric coating composition is deposited by curtain coating. Preferably, the
tie-layer
is laminated to the bituminous base sheet by heating the surface of the base
sheet to
above the softening temperature of the bituminous material, and adhering the
tie-layer to
the base sheet by contacting the base sheet with the tie-layer and permitting
the
bituminous material to partially saturate the tie-layer. Preferably, the
preparative
process further comprises applying pressure while fusing the polymeric coating
composition when a powder coating composition is employed as the polymeric
coating
composition.
In another presently preferred embodiment, the present invention provides a
process for preparing a roofing membrane with high solar heat-reflectance, the
process
comprising laminating a tie-layer to a bituminous base sheet to form an
intermediate
sheet, depositing a solar heat-reflective polymeric coating composition on the
intermediate sheet; and curing the solar heat-reflective polymeric coating
composition to
form a solar heat-reflective coating. In this embodiment, the solar heat-
reflective coating
is preferably deposited by curtain coating. In this embodiment, the process
further
comprises depositing a top or upper coating composition on the solar heat-
reflective
coating to form a top coating layer. Preferably, the top coating composition
is deposited
by curtain coating.
Preferably, in this embodiment the tie-layer is laminated to the bituminous
base
sheet by heating the surface of the base sheet to above the softening
temperature of the
bituminous material, and the tie-layer is adhered to the base sheet by
contacting the
base sheet with the tie-layer and permitting the bituminous material to
partially saturate
the tie-layer.
In a third presently preferred embodiment, the present invention provides a
process for preparing a roofing membrane with high solar heat-reflectance in
which the
process comprises depositing a solar heat-reflective polymeric coating
composition on a
tie-layer to form an intermediate sheet; preferably by curtain coating, curing
the solar
heat-reflective coating composition to form a solar heat-reflective polymeric
coating on
top of the tie-layer; and laminating the tie-layer of the intermediate sheet
to a bituminous
base sheet. Optionally, this process further comprises depositing a top
coating
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composition on the solar heat-reflective polymeric coating to form a top or
upper coating
layer. In this embodiment, the tie-layer is also laminated to the bituminous
base sheet
by heating the surface of the base sheet to above the softening temperature of
the
bituminous material, and adhering the tie-layer to the base sheet by
contacting the base
sheet with the tie-layer and permitting the bituminous material to partially
saturate the
tie-layer. However, in this embodiment, tie-layer forms the lower sub-layer of
the
intermediate sheet.
In another presently preferred embodiment, the heat reflective polymeric
coating
composition is deposited on the tie layer by extrusion coating.
In yet another embodiment, the heat reflective polymeric coating composition
is
deposited on the tie layer by lamination of a preformed film to the tie layer.
The present invention further provides a roof having high solar heat
resistance.
The roof comprises a roofing deck and a roofing membrane with high solar heat
resistance according to the present invention adhered to the roofing deck. In
addition,
the present invention provides a method of constructing a roof having high
solar heat
resistance. The construction method comprises adhering a roofing membrane with
high
solar heat resistance according to the present invention to a roofing deck.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure us a schematic illustration of the structure of solar heat-reflective
roofing
membrane according to a first embodiment of the present invention.
Figure 2 is a schematic illustration of the structure of solar heat-reflective
roofing
membrane according to a second embodiment of the present invention.
Figure 3 is a schematic illustration of a first embodiment of a process
according
to the present invention for preparing a roofing membrane with high solar heat-
reflectance.
Figure 4 is a schematic illustration of a second embodiment of a process
according to the present invention for preparing a roofing membrane with high
solar
heat-reflectance.
Figure 5 is a schematic illustration of a third embodiment of a process
according
to the present invention for preparing a roofing membrane with high solar heat-
reflectance.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the process of the present invention, roofing membranes with high solar
heat
reflectance are formed by combining a reinforcement material as a tie-layer
between the
substrate of suitable bituminous membrane and a solar heat-reflective upper
layer. The
heat-reflective upper layer can be formed by applying a suitable polymeric
coating
composition on top of the tie-layer, by a suitable technique, such as by a
curtain coating
technique, or a spray technique such as by an electrostatic spray technique.
Alternatively, the heat reflective upper lay can be formed by melting or
fusing a suitable
powder coating material in place during manufacturing.
Referring now to the figures in which like reference numerals represent like
elements in each of the several views, there is shown in Figure 1 a schematic
illustration of a first embodiment of a solar heat-reflective roofing membrane
10
according to the present invention. The solar heat-reflective roofing membrane
10 is
comprised of three layers 12, 14, 16. The first layer 12 is a bituminous
membrane, such
as an asphalt-based roofing base sheet, preferably with a self-adhering
backing.
Adhered to the upper surface of the base sheet 12 is a tie-layer 14 formed
from a
reinforcement material such as mineral particles. A solar heat-reflective
coating 16,
preferably formed from a polymeric coating composition, is provided on the tie-
layer 14,
to form an upper surface layer. Liquid applied polymeric coating compositions
including
a carrier such as aqueous dispersions and solutions or dispersions in organic
solvents or
plasticizers can be used. Alternatively, the polymer coating composition can
take the
form of a polymer melt. In addition, polymeric powder coating compositions can
also be
employed.
A schematic illustration of a second embodiment of a solar heat-reflective
roofing
membrane 20 according to the present invention is shown in Figure 2. The solar
heat-
reflective roofing membrane 20 is also comprised of three layers 22, 24, 26.
The first
layer 22 is also bituminous membrane, such as an asphalt-based roofing base
sheet,
preferably with a self-adhering backing. However, adhered to the upper surface
of the
base sheet 22 is a tie-layer 24 comprising a fibrous mat, such as a non-woven
glass
fiber mat. A solar heat-reflective coating 26 is also provided on the tie-
layer 24, to form
an upper surface layer.
The solar heat-reflective roofing products of the present invention, such as
solar-reflective roofing membranes, can be manufactured using conventional
roofing
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production processes, with the addition of one or more curtain coating steps,
one or
more extrusion coating steps, one or more spray coating steps, and/or one or
more
powder coating process steps in the case of some embodiments. Typically,
bituminous
roofing products are sheet goods that include a non-woven base or scrim formed
of a
fibrous material, such as a glass fiber scrim. The base is coated with one or
more
layers of a bituminous material such as asphalt to provide water and weather
resistance
to the roofing product. A self-adhering backing can also be applied to the
lower or rear
surface of the base, and covered with a suitable release sheet. The upper
surface of
the base layer is covered with a tie-layer, and in some embodiments of the
present
invention a liquid applied coating may be applied to the exposed surface of
the tie layer,
by a technique such as curtain coating or electrostatic spray coating. In some
other
embodiments of the present invention, a powder coating, an extrusion coating,
a spray
coating or a roll coating is then applied to the exposed surface of the tie-
layer.
The solar heat-reflective roofing membrane is subsequently employed in
constructing a solar heat-reflective roof according to the present invention.
The roof is
constructed by applying a solar-reflective roofing 'membrane according to the
present
invention to a suitable subroof in the case of new construction, or a suitably
prepared
roofing surface in the case of an existing structure. In constructing the
roof, the upper
surface of the solar-reflective roofing membrane can be covered with mineral
granules
to provide durability, reflect heat and solar radiation, and to protect the
polymeric
coating binder from environmental degradation. Optionally, a further
protective coating
(not shown) could be applied over the solar heat-reflective coating 26.
Figure 3 schematically illustrates a first presently preferred process
according to
the present invention for preparing a roofing membrane 50 with high solar heat-
reflectance. A continuous web of bituminous membrane 30, such as an asphalt-
based
roofing base sheet with a self-adhering backing, is provided from a roll (not
shown) as
the base layer of the roofing membrane 50_ The web of bituminous membrane 30
is fed
to the processing apparatus in the direction shown by the arrows 32. A tie-
layer web 34,
such as a non-woven web of glass fiber, is fed to the processing apparatus in
the
direction shown by the arrow 35. The tie-layer web 34 is adhered to the upper
surface of
the base layer 30 by pressure applied by a first set of heated pressure
rollers 36 to form
an intermediate web 37. Next, a liquid solar heat-reflective coating
composition 38 is
deposited from a curtain coating apparatus 40 on the upper surface of the
intermediate
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web 37 by a coating technique. Alternatively, other methods of applying the
coating
composition 38 to the intermediate web 37 such as electrostatic spray coating,
or
extrusion coating, depending upon the physical characteristics of the coating
composition, can be employed (not shown). For example, the solar heat-
reflective
coating 38 could be in the form of a powder, and could be applied by
conventional
powder coating techniques. As the intermediate web 37 next passes under an
infrared
heater 42, the liquid coating composition 38 is dried to form a continuous
coating 43 on
the top of the intermediate web 37. In the case where an extrusion coating
process is
employed using a thermoplastic polymer, heater 42 may be optional, and a
cooling
means may be employed to bring the surface of the molten thermoplastic polymer
to a
substantially solid state. Optionally, the intermediate web 37 then passes
through a
second set of heated pressure rollers 44 which press the coating composition
43 into the
tie-layer 34 and base layer 30 and provide a uniform, predetermined thickness
to the
roofing membrane 50, and the roofing membrane is taken up on a receiving roll
(not
shown).
Figure 4 schematically illustrates a second presently preferred process
according
to the present invention for preparing a roofing membrane 51 with high solar
heat-
reflectance. In this process, the first presently preferred process is
repeated, except that
after the intermediate web 37 emerges from the second set of pressure rollers
44, a top
coating composition 45 is dispensed from a second applicator 46, such as a
curtain
coating apparatus, onto the upper surface of the coating composition 43 to
form a top
coating layer 48. The top coating composition 46 is preferably cured or
otherwise
solidified to form a continuous top coating layer 48, for example by
application of heat by
a second infrared heater (not shown), and optionally, the resulting roofing
membrane
can be passed through a second set of pressure rollers or calendar rollers
(not shown)
to provide a uniform thickness to the roofing membrane 51.
Figure 5 schematically illustrates a third presently preferred process
according to
the present invention for preparing a roofing membrane 70 with high solar heat-
reflectance. A continuous web of bituminous membrane 52, such as an asphalt-
based
roofing base sheet with a self-adhering backing, is provided as the base layer
of the
roofing membrane 70. The web of bituminous membrane 52 is fed to the
processing
apparatus in the direction shown by the arrows 54. An intermediate web 56
comprising
an inner sub-layer 58 and an outer sub-layer 60 is fed from a roll 57 to the
processing
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apparatus in the direction shown by the arrow 62, The intermediate web 56
comprises a
tie-layer pre-coated with a solar heat-reflective coating composition. Thus,
the inner
sub-layer 58 of the intermediate web 56 is formed as a tie-layer and the outer
sub-layer
60 comprises a solar heat-reflective coating. The intermediate web 56 is
adhered to the
upper surface of the base layer 52 by pressure applied by a set of pressure
rollers or
calendar rollers 64 to form the roofing membrane 70.
Bituminous roofing products, such as the base sheet 30 or 52, are typically
manufactured in continuous processes in which a continuous substrate sheet of
a
fibrous material, such as a continuous felt sheet or glass fiber mat, is
immersed in a
bath of hot, fluid bituminous coating material so that the bituminous material
saturates
the substrate sheet and coats at least one side of the substrate. The reverse
side of
the substrate sheet can be coated with an anti-stick material such as a
suitable mineral
powder or fine sand. Alternatively, the reverse side of the substrate sheet
can be
coated with an adhesive material, such as a layer of a suitable bituminous
material or a
pressure sensitive adhesive, to render the sheet self-adhering. In this case
the
adhesive layer is preferably covered with a suitable release sheet.
In one presently preferred embodiment roofing membrane according to the
present invention is prepared in a batch process, in which rolls of bituminous
base
sheet are fed through a curtain coater to apply the tie-layer and/or the solar
heat-
reflective upper layer to the bituminous base sheet.
The solar-reflective roofing membrane can be formed into roll goods for
commercial or industrial roofing applications. Alternatively, the solar-
reflective roofing
membrane can be cut into conventional shingle sizes and shapes (such as one
foot by
three feet rectangles), slots can be cut in the shingles to provide a
plurality of "tabs" for
ease of installation or for aesthetic effects, additional bituminous adhesive
can be
applied in strategic locations and covered with release paper to provide for
securing
successive courses of shingles during roof installation, and the finished
shingles can be
packaged.
The bituminous material used in manufacturing roofing products according to
the
present invention is derived from a petroleum processing by-product such as
pitch,
'straight-run" bitumen, or "blown" bitumen. The bituminous material can be
modified
with extender materials such as oils, petroleum extracts, and/or petroleum
residues.
The bituminous material can include various modifying ingredients including
polymeric
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materials such as, for example, SBS (styrene-butadiene-styrene) block
copolymers,
resins, flame-retardant materials, oils, stabilizing materials, anti-static
compounds, and
the like. Preferably, the total amount by weight of such modifying ingredients
is not more
than about 15 percent of the total weight of the bituminous material. The
bituminous
material can also include amorphous polyolefins, up to about 25 percent by
weight.
Examples of suitable amorphous polyolefins include atactic polypropylene,
ethylene-
propylene rubber, etc. Preferably, the amorphous polyolefins employed have a
softening point of from about 130 degrees C to about 160 degrees C. The
bituminous
composition can also include a suitable filler, such as calcium carbonate,
talc, carbon
black, stone dust, or fly ash, preferably in an amount from about 10 percent
to 70
percent by weight of the bituminous composite material.
Examples of suitable bituminous membranes for use as base sheets in the
process of the present invention include asphalt roofing membranes such as
asphalt-
based, self-adhering roofing base sheet available from CertainTeed
Corporation, Valley
Forge, Pennsylvania, for example, WinterGuardTM shingle underlayment, a base
sheet
which is impregnated with rubberized asphalt.
When the solar heat-reflective coating composition is to be deposited on or
laminated onto the surface of tie-layer after the tie-layer has been deposited
onto the hot
bituminous surface during the manufacturing of roofing membrane, it is
important to
control the bituminous viscosity or the thickness of the tie-layer such that:
the hot
bituminous coating will not completely bleed through the tie-layer prior to
the application
of the heat reflective coating.
Preferably, the reinforcement material comprises a non-woven web of fibers.
Preferably, the nonwoven web comprises fibers selected from the group of glass
fibers,
polymeric fibers and combinations thereof. Examples of suitable reinforcement
material
for use as a tie-layer include, but not limited to, non-woven glass fiber
mats, non-woven
polyester mats, composite non-woven mats of various fibers, composite woven
fabrics of
various fibers, industrial fabrics such as papermaker's forming fabrics and
papermaker's
canvasses, polymer netting, screen, and mineral particles. The fibers employed
in
preparing the reinforcing material can be spun, blown or formed by other
processes
known in the art. Yarn for forming the reinforcement material can include mono-
filament
yarn, multi-filament yarn, spun yarn, processed yarn, textured yarn, bulked
yam,
stretched yarn, crimped yarn, chenille yarn, and combinations thereof. The
cross-
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section of the yarn employed can be circular, oval, rectangular, square, or
star-shaped.
The yarn can be solid, or hollow. The yarn can be formed from natural fibers
such as
wool and cotton; synthetic materials such as polyester, nylon, polypropylene,
polyvinylidene fluoride, ethylene tetrafluroethylene copolymer, polyethylene
terephthalate, polybutylene terephthalate, polytrimethylene terephthalate,
poly(meth)acrylates, aramide, polyetherketone, polyethylene naphthalate, and
the like,
as well as non-organic materials such as spun glass fibers and metallic
materials, or
combinations thereof.
Non-woven glass fiber mats for use in the process of the present invention
preferably have a weight per unit area of from about 40 to 150 g/m2, more
preferably
form about 70 to 120 g/m2, and still more preferably from about 80 to 100
g/m2,and a
thickness of from about 0.01 to 1 mm. Non-woven glass mats having a weight per
unit
area of about 90 g/m2 (0.018 lb/ft2) are typically employed.
Preferably, the tie-layer has sufficient thickness so that an adequately thick
layer
of solar heat-reflective coating composition can be adhered thereto to provide
effective
solar heat reflectance. Preferably, the tie layer has a thickness of from
about 0.001 cm
to about 0.1 cm, more preferably from about 0.001 cm to about 0.03 cm.
Examples of mineral particles that can be used as tie layer materials include
conventional roofing granules. In the present invention, colored, infrared-
reflective
granules, such as disclosed in U.S. Patent Application Serial No. 10/679,898,
filed
October 6, 2003, can be mixed with conventional roofing granules.
Alternatively,
colored, infrared-reflective granules can be substituted for conventional
roofing granules
to enhance the solar-heat reflectance of the solar-reflective roofing
membranes of the
present invention. When mineral particles are employed as the reinforcement
material,
it is preferred that the mineral particles have an average particle size of
from about 180
to about 850 pm. Mineral particles may function as a tie layer for holding the
polymeric
coating on the roofing sheet. For example, the tie layer coat may adhere
better to the
granules than to the bituminous base sheet and the mineral particles may
adhere to
both the bituminous base sheet and to the powder coating. In this sense the
tie layer is
not necessarily a reinforcement material in the sense of reinforcing the
sheet, but rather
the tie layer tends to enhance the holding power of the tie layer to the
surface of the
bituminous sheet.
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Polymeric coating compositions are preferably employed in several embodiments
of the present invention to form the solar heat-reflective upper layer, or a
portion thereof.
In particular, in one presently preferred embodiment, the upper layer is
formed from a
first polymeric coating composition including at least one first polymeric
coating binder.
In another presently preferred embodiment, the upper layer is formed from an
inner sub-
layer and an outer sub-layer. In this case, the outer sub-layer is preferably
formed from
a first polymeric coating composition including at least one first polymeric
coating binder,
and the inner sub-layer is formed from a second polymeric coating composition
including
at least one second polymeric coating binder. In another embodiment, the outer
layer
from a sheet or film preferably formed from a polymeric composition and the
inner layer
is formed from a polymeric coating composition including at least one
polymeric binder.
The polymeric coating compositions employed in the present invention can be
liquid polymeric compositions such as solutions in which a suitable polymeric
binder is
dissolved or dispersed in an organic solvent or carrier, or aqueous polymer
compositions
such as aqueous dispersions of a suitable polymeric binder. Alternatively,
powder
coating compositions, such as powder coating compositions including a suitable
polymeric binder in solid form, can be employed. Whatever the physical form of
the
polymeric coating composition, the polymeric binder is preferably selected to
provide
good exterior durability to the roofing membranes of the present invention.
Thus,
polymeric binders with good uv resistance, such as poly(meth)acrylate
("acrylic"), and
fluorinated polymer binders, are preferred.
Examples of polymeric materials that can be employed as polymeric binders in
the polymeric coating compositions of the present invention include acrylic
copolymers,
polyesters, polyamides, epoxies, nonacid-containing polyolefins, polyolefin
alloys,
polypropylene, acid-containing polyolefins, polyvinyl chloride, polyester
block amide,
ethylene-chlorotrifluorethylene, and polyvinylidene fluoride.
Preferably, the monomer composition of the polymeric binder is selected to
provide a glass transition temperature of the polymer from about 66 degrees C
to about
204 degrees C (150 degrees F ¨ 400 degrees F). Alternatively, in the case of a
crystalline or semicrystalline thermoplastic polymeric binder, the composition
is selected
to provide a melting temperature greater than about 90 degrees C, more
preferably
greater than about 110 degrees C, and preferably less than about 210 degrees
C.
CA 02581032 2007-03-07
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The polymeric coating compositions employed in the process of the present
invention may also include pigments, such as solar heat-reflective pigments
and coloring
pigments, dyes, biocides, flow control agents, thickeners, coalescents to
promote film
formation, solvents (in the case of aqueous dispersions), agents to adjust
surface
tension, viscosity control agents, light stabilizers, antioxidants, and other
components.
When the polymeric coating compositions of the present invention are in a
fluid
state, such as when they comprise an aqueous dispersion, an non-aqueous
solution or
dispersion, or a melt, a fluid coating application method can be used to apply
such
polymeric coating compositions in the process of the present invention.
Examples of
fluid coating application techniques that can be employed include curtain
coating,
gravure coating, dip coating, rod coating, knife coating, air-knife coating,
blade coatingõ
forward roll coating, reverse roll coating, slot coating, and extrusion
coating. Factors
affecting the choice of a method of a coating are discussed, e.g., in Cohen,
E. et al.
Modern Coating and Drying Technology (Advances in Interfacial Engineering
Series),
(Wiley-VCH 1992) pp. 10-18.
The powder coating materials optionally employed as polymeric coating
compositions in the process of the present invention are typically dry, solid
powder
materials that include a polymeric resinous binder with a melting temperature
above
ambient temperature and optional pigments, extenders, flow control agents,
plasticizers,
reactive diluents, and/or other additives. Powder coating materials or
compositions for
use in the present invention preferably include both a polymeric binder and a
solar-
reflective pigment.
Suitable powder coating material should have excellent outdoor durability; a
melting temperature for application of between 66 degrees C to about 204
degrees C
(150 degrees F ¨400 degrees F); and low viscosity upon melting to completely
impregnate the tie-layer in a relatively short period of time. By "low
viscosity" is meant a
viscosity of from about 50 centipoise to 3000 centipoise,
Examples of suitable powder coating compositions include thermoplastic and
thermoset powder coating compositions. Thermoplastic powder coating
compositions
are frequently employed to provide coating of at least about 250 microns.
Thermosetting
powder coating compositions are frequently employed to provide thinner
coatings, such
as coatings with a thickness of from about 20 to 80 microns. Suitable powder
coating
polymeric materials include, but are not limited to, acrylic and related
copolymers,
CA 02581032 2007-03-07
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polyesters, polyamides, epoxies, polyolefin and its alloys, polypropylene,
acid containing
polyolefins such as polyethylene acrylic acid or polyethylene methacrylic
acid, polyvinyl
chloride, polyester block amide, ethylene chlorotnfluorethylene, or
polyvinylidene fluoride
or other fluorinated polymers or copolymers. Examples of thermosetting
materials
thermoplastic materials include polyamide, polyethylene, polypropylene,
polyvinyl
chloride, polyester, and polyvinylidene fluoride thermoplastic materials.
Preferably, a powder coating composition having good exterior durability and
weatherability characteristics is employed. Examples of powder coating
compositions
Powder coating compositions for use in the present invention are preferably
pigmented with solar heat-reflective pigments or fillers in order to produce
an upper
surface coating of high solar reflectance. Examples of suitable heat-
reflective pigments
In addition, powder coating compositions for use in the preparative process of
the
present invention can include other components, such as curing agents or
hardeners,
extenders, and additives such as thixotropes, flow modifiers, and the like.
25 Examples of heat- or infrared-reflective pigments that can be employed
include
colored infrared-reflective pigments and white infrared-reflective pigments.
Upper surface coatings for use in preparing roofing membranes according to the
present invention preferably include at least one infrared-reflective pigment.
The at least
one infrared-reflective pigment can be a colored infrared-reflective pigment,
a white
CA 02581032 2007-03-07
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Preferably, in the upper surface coating composition, when a colored infrared-
reflective pigment is employed, the colored infrared-reflective pigment
comprises from
about 2 percent by weight to about 40 percent by weight of the coating
composition.
More preferably, the colored infrared-reflective pigment comprises about 5
percent by
weight to about 35 percent by weight of the coating composition.
Preferably, in the upper surface coating composition, when a white infrared
pigment, such as titanium dioxide, is employed, the white infrared-reflective
pigment
comprises from about 2 percent by weight to about 40 percent by weight of the
coating
composition. More preferably, the white infrared-reflective pigment comprises
about 10
percent by weight to about 35 percent by weight of the coating composition.
Still more
preferably, the white infrared-reflective pigment comprises from about 25
percent by
weight to about 35 percent by weight of the coating composition.
Preferably, in the upper surface coating composition, when a combination of a
white infrared-reflective pigment, such as titanium dioxide, and a colored
infrared-
reflective pigment, is employed, the combination of the white infrared-
reflective pigment
and the colored infrared-reflective pigment comprises from about 2 percent by
weight to
about 40 percent by weight of the coating composition. Preferably, the colored
infrared-
reflective pigment comprises from about 2 percem by weight to about 10 percent
by
weight of the coating composition, and the white infrared-reflective pigment
comprises
from about 25 percent by weight to about 35 percent by weight of the coating
composition.
Preferably, the upper surface coating composition further comprises at least
one
infrared-reflective functional pigment selected from the group consisting of
light-
interference platelet pigments including mica, light-interference platelet
pigments
including titanium dioxide, mirrorized silica pigments based upon metal-doped
silica, and
alumina.
When alumina is employed as the at least one infrared-reflective pigment, the
alumina (aluminum oxide) preferably has a particle size less than #40 mesh
(425
microns), preferably between 0.1 micron and 5 microns, and more preferably
between
0.3 micron and 2 microns. It is preferred that the alumina includes greater
than 90
percent by weight A1203, and more preferably, greater than 95% by weight
A1203.
CA 02581032 2007-03-07
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Optionally, the upper surface coating composition can include at least one
coloring material selected from the group consisting of granule coloring
pigments and
UV-stabilized dyes.
Preferably, the at least one colored, infrared-reflective pigment comprises a
solid
solution including iron oxide, such as disclosed in U.S. Patent 6,174,360,
incorporated
herein by reference. The colored infrared-reflective pigment can also comprise
a near
infrared-reflecting composite pigment such as disclosed in U.S. Patent
6,521,038,
incorporated herein by reference. Composite pigments are composed of a near-
infrared
non-absorbing colorant of a chromatic or black color and a white pigment
coated with the
near infrared-absorbing colorant. Near-infrared non-absorbing colorants that
can be
used in the present invention are organic pigments such as organic pigments
including
azo, anthraquinone, phthalocyanine, perinone/perylene, indigo/thioindigo,
dioxazine,
quinacridone, isoindolinone, isoindoline, diketopyrrolopyrrole, azomethine,
and
azomethine-azo functional groups. Preferred black organic pigments include
organic
pigments having azo, azomethine, and perylene functional groups.
Examples of near infrared-reflective pigments available from the Shepherd
Color
Company, Cincinnati, OH, include Arctic Black 10C909 (chromium green-black),
Black
411 (chromium iron oxide), Brown 12 (zinc iron chromite), Brown 8 (iron
titanium brown
spinel), and Yellow 193 (chrome antimony titanium).
Light-interference platelet pigments are known to give rise to various optical
effects when incorporated in coatings, including opalescence or pearlescence.
Surprisingly, light-interference platelet pigments have been found to provide
or enhance
infrared-reflectance of roofing granules coated with compositions including
such
pigments.
Examples of light-interference platelet pigments that can be employed in the
process of the present invention include pigments available from Wenzhou
Pearlescent
Pigments Co., Ltd., No. 9 Small East District, Wenzhou Economical and
Technical
Development Zone, Peoples Republic of China, such as Taizhu TZ5013 (mica,
rutile
titanium dioxide and iron oxide, golden color), TZ5012 (mica, rutile titanium
dioxide and
iron oxide, golden color), TZ4013 (mica and iron oxide, wine red color),
TZ4012 (mica
and iron oxide, red brown color), TZ4011 (mica and iron oxide, bronze color),
TZ2015
(mica and rutile titanium dioxide, interference green color), TZ2014 (mica and
rutile
titanium dioxide, interference blue color), TZ2013 (mica and rutile titanium
dioxide,
CA 02581032 2007-03-07
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interference violet color), TZ2012 (mica and rutile titanium dioxide,
interference red
color), TZ2011 (mica and rutile titanium dioxide, interference golden color),
TZ1222
(mica and rutile titanium dioxide, silver white color), TZ1004 (mica and
anatase titanium
dioxide, silver white color), TZ4001/600 (mica and iron oxide, bronze
appearance),
TZ5003/600 (mica, titanium oxide and iron oxide, gold appearance), TZ1001/80
(mica
and titanium dioxide, off-white appearance), TZ2001/600 (mica, titanium
dioxide, tin
oxide, off-white/gold appearance), TZ2004/600 (mica, titanium dioxide, tin
oxide, off-
white/blue appearance), 1Z2005/600 (mica, titanium dioxide, tin oxide, off-
white/green
appearance), and TZ4002/600 (mica and iron oxide, bronze appearance).
Examples of light-interference platelet pigments that can be employed in the
process of the present invention also include pigments available from Merck
KGaA,
Darmstadt, Germany, such as Iriodin pearlescen1 pigment based on mica covered
with
a thin layer of titanium dioxide and/or iron oxide; Xirallic TM high chroma
crystal effect
pigment based upon A1203 platelets coated with metal oxides, including
Xirallic T 60-10
WNT crystal silver, Xirallic T 60-20 WNT sunbeam gold, and Xirallic F 60-50
WNT
fireside copper; ColorStream TM multi color effect pigments based on Si02
platelets
coated with metal oxides, including ColorStream F 20-00 WNT autumn mystery and
ColorStream F 20-07 WNT viola fantasy; and ultra interference pigments based
on TiO2
and mica.
Examples of mirrorized silica pigments tha1 can be employed in the process of
the present invention include pigments such as Chrom BriteTM CB4500, available
from
Bead Brite, 400 Oser Ave, Suite 600, Hauppauge, N.Y. 11788.
Upper surface coatings can include at least one infrared-reflective white
pigment.
Examples of white pigments that can be employed in the process of the present
invention include rutile titanium dioxide, anatase titanium dioxide,
lithopone, zinc sulfide,
zinc oxide, lead oxide, and void pigments such as spherical styrene/acrylic
beads
(Ropaque beads, Rohm and Haas Company), and hollow glass beads having
pigmentary size for increased light scattering. Preferably, the at least one
reflective
white pigment is selected from the group consisting of titanium dioxide, zinc
oxide and
zinc sulfide.
It is preferred that the at least one reflective white pigment comprises from
about
10 percent by weight to about 40 percent by weight of the upper surface
coating
composition. It is more preferred that the at least one reflective white
pigment comprises
CA 02581032 2007-03-07
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from about 20 percent by weight to about 30 percent by weight of the upper
surface
coating composition.
The polymeric coating compositions of the present invention are prepared by
admixing the solar heat-reflective pigment(s) with the polymeric resinous
binder and
other optional additives and then subsequently extruding and milling the
mixture.
Alternatively, the polymeric coating compositions of the present invention can
be
prepared by blending the solar heat-reflective pigment(s) with the polymeric
resinous
binder after the binder and other optional additives have been mixed, extruded
and
milled. In the alternative, powder coating compositions in accordance with the
present
invention can be prepared by blending the solar heat-reflective pigment(s)
with a
polymeric resinous binder after the powder and other optional additives have
been
mixed, extruded and milled, and subsequently subjecting the blend to
compressive
forces to bond the solar heat-reflective-pigment(s) to the surface of the
milled particles of
the polymeric resinous binder,
Preferably, the infrared-reflective upper surface coating is provided in a
thickness
effective to render the coating opaque to infrared radiation, such as a
coating thickness
of at least about 75 microns. However, advantageous properties of the present
invention can be realized with significantly lower coating thicknesses, such
as at a
coating thickness of from about 2 microns to about 25 microns, including at a
coating
thickness of about 5 microns.
Optionally, the upper surface coating composition includes at least one
extender
pigment such as barium sulfate, wollastanite, talc, calcium carbonate, or
clay.
In a presently preferred process of the present invention, a roofing membrane
of
the present invention is produced by first laminating a tie-layer onto a hot
asphaltic
surface of a membrane substrate to adhere the tie-layer.
In the case of a fibrous web tie-layer, the lamination to the asphaltic
surface
serves to partially impregnate the tie-layer with material from the substrate
layer. It is
preferred that the tie-layer is well adhered to the substrate membrane and the
asphalt
coating does not over-saturate the tie-layer in order that the upper layer can
be properly
adhered to the tie-layer.
In another presently preferred process of the present invention, a roofing
membrane of the present invention is produced by first forming a tie-layer
comprised of
particulate material on a hot asphaltic surface of a membrane substrate to
adhere the
CA 02581032 2007-03-07
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tie-layer. The particulate material, such as roofing granules, is deposited on
the hot
asphaltic surface such that the particulate material at least partially
penetrates into and
at least partially protrudes from the asphaltic surface such that a secure
mechanical
bond is formed when the heated surface cools. It is preferred that the
particles of the tie-
layer be well adhered to the substrate membrane and the asphalt coating are
not too far
embedded in the asphaltic surface in order that the upper layer can be
properly adhered
to the tie-layer.
Subsequently, a suitable amount of powder coating material is deposited onto
the upper surface of the tie-layer, followed by heating to melt or fuse the
powder coat in
place. This can be accomplished by direct infrared heat lamps, localized
microwave
irradiation, direct application of hot air by passage through a convection
oven or the like,
impingement heating, or by heated hot press rolls, or a combination thereof.
In general, the method of application depends upon the chemical and physical
characteristics of the polymeric powder coating composition. In the case of
thermosetting polymer systems, fine-particle sized powder can be applied to
the tie-coat
surface by suitable spray equipment or by gravity deposition from a suitable
reservoir or
hopper. In the case of thermoplastic materials, fluidized bed application of
the web can
be used, although in general it is preferred to coat only one side of the
bituminous
membrane with the powder coating material.
Conventional powder coating application equipment can be used to apply the
polymeric powder, such as electrostatic spray equipment employing corona
charging or
triboelectric charging of the powder coating particles. Alternatively, an air
spray system
that delivers the powder onto a substrate having sufficient heat to soften the
polymeric
powder for sticking to the surface can be used. Preferably, the application
equipment
includes provisions for precision application of the powder coating
composition to the tie
layer, and collection and recycling of excess powder coating composition in
order to
increase the efficiency and lower the cost of the process. When electrostatic
spray
equipment is employed to deliver the polymeric powder composition to the tie
layer, it is
preferred that a suitable electrical charge be provided on the tie layer or
that the tie layer
be electrically grounded so as to increase electrostatic attraction between
the tie layer
and the polymeric powder composition. For example, the tie layer can be formed
from a
non-woven material that includes electrically conductive fibers.
CA 02581032 2007-03-07
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Preferably, the powder coating is applied to the intermediate web or substrate
in
sufficient quantity so as to completely cover the surface, while forming a
thin coating film
after the powder coating is fused. Preferably, the powder coating material is
applied to
the intermediate substrate in sufficient quantity to provide a coating of from
about 25 to
about 300 microns in thickness, more preferably from about 50 to about 200
microns,
with a thickness of from about 75 to about 175 microns being especially
preferred.
The method of fusing and/or curing the powder coating composition depends on
the chemical and physical properties of the polymeric powder, including the
average
particle size of the powder and particle size distribution, and the chemical
properties of
the crosslinking agent, if any, present in the material. If the powder coating
composition
includes a suitable heat-activated crosslinking agent, infrared heat can be
used.
Similarly, if the powder coating composition includes a UV-activated
crosslinking agent,
ultraviolet radiation can be used to cure the powder coating composition. In
some other
instances, a higher energy actinic radiation source such as an electron beam
or gamma
source can be used to impart cure to the powder coating composition.
In one presently preferred embodiment of the present invention, a tie-layer is
pre-
coated with a solar heat-reflective coating composition through a process such
as
extrusion coating, lamination, spray, curtain or roller coating, and the
coating
composition is then cured to form an intermediate web. The resulting
intermediate web
includes an inner sub-layer formed by the tie-layer and an outer sub-layer
formed by the
cured solar heat-reflective coating composition, although the inner sub-layer
and outer
sub-layer can interpenetrate. Preferably, the solar heat reflective coating
composition is
cured prior to complete penetration of the coating throughout the tie-layer.
It is desirable
that the coating composition does not completely encapsulate the tie-layer, so
that the
lower, exterior surface of the tie-layer can adhere properly to the asphalt
substrate.
Partial bleeding through of the tie layer by the heat reflective coating is
acceptable,
provided that sufficient adhesion between the intermediate web and the base
sheet
layers can be achieved. Other methods of coating the tie layer on one side
known in the
art can be employed to form the intermediate web Examples of suitable coating
materials include thermoplastics. thermoplastic elastomers and their mixtures,
UV
curable coatings, powder coatings, latex coatings and inorganic coatings.
A protective overcoat or top coat can also be applied over the solar heat-
reflective coating composition. The solar heat-reflective upper layer in this
case thus
CA 02581032 2007-03-07
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comprises a top coat or overcoat applied to the solar heat-reflective coating.
For
example, in order to help protect the cured or fused solar heat-reflective
coating
composition from environmental degradation, an overcoat of a suitable coating
material
can be applied to the fused or cured solar heat-reflective coating
composition.
Examples of protective overcoat compositions include fluoropolymer coatings,
acrylic
modified fiuoropolymer emulsions, all-acrylic coating materials, and in
particular solvent-
based and water-based acrylic coating materials with good adhesion to the
powder
coating composition employed. The overcoat composition includes a suitable
binder,
and optional pigment, such as a suitable infrared-reflective pigment.
The upper layer can include a very durable layer of top coating and a second
layer of solar heat-reflective coating, preferably in the form of a powder
coating
composition with good workability to penetrate and fill the tie layer, under
the top layer.
The upper layer itself can be formed from a powder coating composition having
suitable
material properties. Such a multi-layer construction has the advantage of
permitting the
top layer composition to provide exceptional outdoor durability for roof
longevity and
other functionalities, while opening wider material choices for the solar heat
reflective
under-layer. For example, when a durable material is employed for the top
layer, a less
weatherable powder coating having better melt-flowing properties at lower
processing
temperatures than would otherwise be achievable can be employed for the under-
layer.
Thus, the top coating composition is preferably formulated to provide good
exterior
durability. The top coating composition can also provided additional
functionalities such
as anti-microbial effects, slip resistance, better fire resistance, or self-
cleaning effects.
Examples of suitable materials for use as the top coating include
fluoropolymers such as
PVDF (Kynar Aquatec and Ultraflex from Arkema) UV-curable coatings, acrylic
latex
based coatings, or silicone emulsions. The top layer can be applied to the
surface of
under-layer through methods such as curtain coating, spraying, extrusion
coating, or
roller coating. The under-layer is preferably formed from a coating
composition including
solar heat-reflective pigments or fillers, and a binder having a melt
temperatures from
about 93 degrees C to about 121 degrees C (about 200 degrees F to about 250
degrees
F), and such that the under-layer composition becomes tack-free for
temperatures below
about 66 degrees C (about 150 degrees F).
The present invention also provides an improved roof having high solar heat
resistance. The roof comprises a roofing deck, and a roofing membrane with
high solar
CA 02581032 2007-03-07
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heat resistance, according to the present invention, adhered to the roofing
deck.
Conventional roofing decks, such as decks formed from plywood, steel, cement,
et al.
can be covered with a roofing membrane according to the present invention. In
addition,
the present invention provides a method of constructing a roof having high
solar heat
resistance. The roof construction method comprises adhering to a roofing deck
a roofing
membrane with high solar heat resistance according to the present invention.
The following examples are provided to better disclose and teach processes and
compositions of the present invention. They are for illustrative purposes
only, and it
must be acknowledged that minor variations and changes can be made without
materially affecting the spirit and scope of the invention as recited in the
claims that
follow.
Example 1
A 12.7 cm by 12.7 cm (5 inch x 5 inch) piece of an asphalt-based, self-
adhering
roofing base sheet (WinterGuard, commercially available from CertainTeed
Corporation, Valley Forge, PA) is first heated to about 50 degree C and then a
non-
woven glass fiber mat (1.8 lb. mat available from Johns Manville Corp.) is
laminated
onto the self-adhering side of the base sheet using a 12.3 kg (27 lb.) roller.
A white
powder coat mixture consisting of 6.05g clear acrylic powder (Ultra Detail
from Mark
Enterprises, Anaheim, CA) and 2.66g of 1102 white pigment (TiPure R-102 from
DuPont Corp.) is then deposited onto the surface of the glass fiber mat using
a
perforated hand shaker until the surface is covered with a uniform layer of
the power
coat. The resultant sheet is then heated under infrared heat lamps to a
surface
temperature of 116 ¨121 degrees C (240-250 degrees F) until the powder coat is
completely melted and the tie-layer filled to form a uniform white coating.
The
resultant sample of roofing membrane has an averaged solar reflectance of
76.5% as
measured by the ASTM C-1549 method.
Example 2
A 12.7 cm by 12.7 cm (5 inch x 5 inch) of an asphalt-based, self-adhering
roofing base sheet (WinterGuard, commercially available from CertainTeed) is
first
heated to about 50*C and then a non-woven glass fiber mat (1.81 lb. mat
available
from Johns Manville Corp.) is laminated onto the self-adhering side of the
base sheet
using a 12.3 kg (27 lb.) roller. A white powder coat of nylon 11 with melting
temperature of about 186 degrees C (Rilsan 11 polyamide from Atofina
Chemicals,
CA 02581032 2007-03-07
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Inc., Philadelphia, PA) is then deposited onto the surface of the glass mat
using a
perforated hand shaker until the surface is covered by a uniform layer of the
powder
coat. The resultant sheet is then pressed under a hot plate with the top plate
set at 193
degrees C (380 degrees F) and bottom plate set at room temperature using
pressing
load of 3630 kg (8000 lb.), holding time of 15 seconds, and a gauge bar of
0.24 cm
(3/16 inch) to prevent over-press. The resultant sample of roofing membrane
has a
very smooth surface finish and an averaged solar reflectance of 77.6%.
Example 3
Roofing membranes having inert mineral particles derived from crushed slate
rocks as tie layer (particle sizes ranging from US mesh #20 to #70, available
from
CertainTeed Corp., Glenwood, AR) were coated with acrylic latex containing
25wt% TiO2
as solar heat reflective material. The coatings were applied by air-assisted
spraying
nozzles (Kinetix Airspray LP spray gun with 0.090" nozzle tip, available from
Nordson
Corp., Amherst, OH), electrostatic spray (ES) with rotary atomizer (RA-20
Rotary
Atomizer available also from Nordson Corp), and the combination of both. The
spray
applications were carried out at conveyor speed of 50 feet per minute. Table 1
lists the
spraying conditions and the results of their color and solar reflectance
measurements.
In Run #6, a primer of acrylic based water emulsion was first sprayed on the
membranes, followed by a topcoat of same acrylic latex. The coatings were then
cured
to form the reflective membrane. These examples show that coated membranes
have
significantly high solar reflectance and excellent adhesion to the asphalt
substrate by the
tie layer, as indicated by no peeling/cracking after 3000 hours in the xenon-
arc
weatherometer according to ASTM G-155 test methods.
Table 1
Run Sprayer Type Color Reading [%
Solar I
No. L* a*
b* ' Reflectance ,
1 Control¨no coating I 26.95 0.29 3.03 1
6.5
1
2 Electrostatic spray (ES) with 3 rotary 1 94.57 -1.07 0.34
71.4
atomizer
3 2 spray guns and ES with 2 rotary 93.1 -1_11 0.03
68.9
atomizers
4 3 spray guns I 92.32 -1.22 -0.36
68.5
_________________________________________ ¨ ________
CA 02581032 2013-08-08
- 25 -
1 spray gun and ES with 2 rotary 94.11 I -1.09 0.35 I 71.9
atomizers
6 Primer: ES with 3 rotary atomizer 1 97.71 -0.97 0.66
81.2
1 Topcoat: ES with 2 rotary atomizer
Example 4
Roofing membranes having inert mineral particles derived from crushed rhyolite
5 rocks as tie layer (particles ranging from US mesh #10 to #40, Flintglas
Mineral
Surfaced Cap Sheet, available from CertainTeed Corp., Piedmont, MO) were
coated
with acrylic latex containing 21.4 weight percent titanium dioxide as solar
heat reflective
material. The coating was applied by a curtain coater at a curtain height of 8
inches
(Koch Model #80 curtain coater, Koch Manufacturing LLC, Evansville, IN) and
conveyor
speed of 120 feet per minute. The coating was applied at a wet film thickness
of 17 mils.
The coated membranes were then cured in a forced-air oven at 180 degrees F (82
degrees C) with an oven dwell time of one minute. The coated membrane had a
color
reading of L*=91.93, a*=-0.99, b*=0.87 as measured by HunterLab Labscan XE
colorimeter and an averaged solar reflectance of 73_1 percent as measured by
the
ASTM C1145 method. In comparison, a control sample with no coating had a color
reading of L*=62.24, a*=-0.45, b*=0,88, and a solar reflectance of 26 percent.
The
coated membrane passes 2000 hours in xenon-arc weatherometer without peeling,
crack, or coating failure, which shows that the coarser tie layer also help in
promoting
the adhesion between the coating and the asphalt substrate.
Various modifications can be made in the details of the various embodiments of
the processes, compositions and articles of the present invention, all within
the scope
of the invention and defined by the appended claims.
