U.S. patent application number 14/247761 was filed with the patent office on 2014-09-04 for solar heat-reflective roofing granules, solar heat-reflective shingles and process for producing the same.
The applicant listed for this patent is Tihana Fuss, Husnu M. Kalkanoglu, Ming Liang Shiao, Walter T. Stephens. Invention is credited to Tihana Fuss, Husnu M. Kalkanoglu, Ming Liang Shiao, Walter T. Stephens.
Application Number | 20140248467 14/247761 |
Document ID | / |
Family ID | 43855075 |
Filed Date | 2014-09-04 |
United States Patent
Application |
20140248467 |
Kind Code |
A1 |
Shiao; Ming Liang ; et
al. |
September 4, 2014 |
SOLAR HEAT-REFLECTIVE ROOFING GRANULES, SOLAR HEAT-REFLECTIVE
SHINGLES AND PROCESS FOR PRODUCING THE SAME
Abstract
A process for preparing roofing granules includes forming kaolin
clay into green granules and sintering the green granules at a
temperature of at least 900 degrees Celsius to cure the green
granules until the crystalline content of the sintered granules is
at least ten percent as determined by x-ray diffraction.
Inventors: |
Shiao; Ming Liang;
(Collegeville, PA) ; Fuss; Tihana; (Derry, NH)
; Kalkanoglu; Husnu M.; (Swarthmore, PA) ;
Stephens; Walter T.; (Cleveland, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Shiao; Ming Liang
Fuss; Tihana
Kalkanoglu; Husnu M.
Stephens; Walter T. |
Collegeville
Derry
Swarthmore
Cleveland |
PA
NH
PA
OH |
US
US
US
US |
|
|
Family ID: |
43855075 |
Appl. No.: |
14/247761 |
Filed: |
April 8, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12886721 |
Sep 21, 2010 |
8722140 |
|
|
14247761 |
|
|
|
|
61244627 |
Sep 22, 2009 |
|
|
|
Current U.S.
Class: |
428/149 ;
427/186; 501/2 |
Current CPC
Class: |
C04B 2235/95 20130101;
C04B 35/636 20130101; C04B 2235/5472 20130101; C04B 2235/5481
20130101; C04B 2235/528 20130101; C04B 33/32 20130101; C04B
2235/349 20130101; E04D 2001/005 20130101; Y10T 428/24413 20150115;
C03C 10/00 20130101; C04B 35/62695 20130101; C04B 2235/5427
20130101; Y02B 80/34 20130101; C04B 33/04 20130101; E04D 1/16
20130101; Y02B 80/00 20130101; C04B 2235/9646 20130101; C04B
2235/9661 20130101; C04B 2235/5463 20130101; Y02A 30/254 20180101;
C04B 2235/3217 20130101; C04B 35/10 20130101; Y10T 428/24421
20150115; C04B 35/18 20130101; Y02A 30/255 20180101; C04B 35/64
20130101; C04B 2235/5436 20130101 |
Class at
Publication: |
428/149 ;
427/186; 501/2 |
International
Class: |
E04D 1/16 20060101
E04D001/16; C03C 10/00 20060101 C03C010/00 |
Claims
1. Synthetic roofing granules comprising at least one sintered
aluminosilicate, the granules having a crystalline content of at
least 70 percent as determined by x-ray diffraction.
2. Synthetic roofing granules according to claim 1 having a
crystalline content of at least 90 percent.
3. Synthetic roofing granules according to claim 1 comprising
sintered bauxite.
4. Synthetic roofing granules according to claim 1 comprising
sintered kaolin clay.
5. Synthetic roofing granules according to claim 1 wherein the
amorphous content is greater than about five percent.
6. Synthetic roofing granules according to claim 1 containing less
than three percent silica.
7. A roofing product with high solar heat reflectance prepared
according the process comprising: (a) providing a ceramic-forming
material comprising at least one aluminosilicate; (b) forming the
ceramic-forming material into green granules; (c) sintering the
green granules at a temperature of at least 900 degrees Celsius
until the crystalline content of the sintered granules is at least
ten percent as determined by x-ray diffraction; (d) providing a
roofing material having an upper surface; and (e) applying the
sintered granules to the upper surface of the roofing material.
8. A roofing product according to claim 7 wherein the roofing
material is a roofing sheet.
9. A roofing product according to claim 8 wherein the roofing sheet
is a bituminous roofing sheet.
10. A roofing product according to claim 7, wherein the green
granules are sintered until the crystalline content of the granules
is at least 70 percent.
11. A roofing product according to claim 10, wherein the granules
are sintered at a temperature of at least 1450 degrees Celsius
until the crystalline content of the granules is about 100 percent
as determined by x-ray diffraction.
12. A roofing product according to claim 7, wherein the
ceramic-forming material is formed into green granules by mixing
the ceramic-forming material with a liquid to form a mixture, the
mixture being formed into pellets, and the pellets being screened
to provide green granules.
13. A roofing product according to claim 7, wherein the
ceramic-forming material is formed into green granules having a
predetermined particle-size distribution.
14. A roofing product according to claim 13 wherein the
ceramic-forming material is formed into at least two different
classes of green granules, each class of green granule being
characterized by a predetermined average particle size, the green
granules being sintered to provide at least two size classes of
sintered granules.
15. A roofing product according to claim 7, wherein the shape of
the granules and the granule particle-size distribution are
selected to provide at least 85 percent surface coverage when the
roofing granules are applied to the upper surface of the roofing
material.
16. A roofing product according to claim 7 wherein the process
further comprises selecting sintered granules from at least two
different classes prior to applying the sintered granules in the
upper surface of the roofing material, the sintered granules being
selected to provide a predetermined surface coverage of the roofing
material.
17. A roofing product according to claim 16 wherein at least two
different classes of sintered granules are applied sequentially to
the upper surface of the roofing material.
18. A bituminous roofing product according to claim 7 wherein the
process further comprises applying conventional colored roofing
granules to the roofing material.
19. A roofing product according to claim 7 wherein the process
further comprises applying a liquid binder composition to the upper
surface of the roofing material after the sintered granules have
been applied, the liquid binder composition being selected from the
group consisting of acrylic emulsions, acrylic solutions,
thermoplastic polymers, fluoropolymer emulsions, epoxy resins, UV
curable resins, radiation curable resins, alkaline metal silicates,
sol-gel solutions, silicone resins, and silica binders.
20. A process for forming bituminous roofing products with high
solar heat reflectance, the process comprising: (a) providing a
ceramic-forming material comprising at least one aluminosilicate;
(b) providing base particles comprising material thermally stable
up to a temperature of at least 900 degrees Celsius; (c) applying
the ceramic-forming material to the base particles to form a green
coating layer on the base particles to form green granules; (d)
sintering the green granules at a temperature of at least 900
degrees Celsius until the crystalline content of the coating layer
of the granules is at least ten percent as determined by x-ray
diffraction; (e) providing a bituminous roofing sheet material
having an upper surface; and (f) applying the sintered granules in
the upper surface of a bituminous roofing sheet material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of pending U.S. patent
application Ser. No. 12/886,721 filed Sep. 21, 2010, which claims
the priority of U.S. Provisional Patent Application No. 61/244,627,
filed Sep. 22, 2009, each incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to protective granules for
asphalt roofing shingles, roofing shingles employing such granules,
and processes for making such granules and shingles.
[0004] 2. Brief Description of the Prior Art
[0005] Sized mineral rocks are commonly used as granules in roofing
applications to provide protective functions to the asphalt
shingles. Roofing granules are generally used in asphalt shingles
or in roofing membranes to protect asphalt from harmful ultraviolet
radiation. Roofing granules typically comprise crushed and screened
mineral materials, which can be coated subsequently with a binder
containing one or more coloring pigments, such as suitable metal
oxides. The granules are employed to provide a protective layer on
asphaltic roofing materials such as shingles, and to add aesthetic
values to a roof.
[0006] Depending on location and climate, shingled roofs can
experience very challenging environmental conditions, which tend to
reduce the effective service life of such roofs. One significant
environmental stress is the elevated temperature to which roofing
shingles are subjected under sunny, summer conditions.
[0007] Mineral-surfaced asphalt shingles, such as those described
in ASTM D0225 or D03462, are generally used in steep-sloped roofs
to enhance the water-shedding function while adding aesthetically
pleasing appearance to the roofs. The asphalt shingles are
generally constructed from asphalt-saturated roofing felts and
surfaced by pigmented color granules, such as those described in
U.S. Pat. No. 4,717,614. Asphalt shingles coated with conventional
roofing granules are known to have low solar heat reflectance, and
hence will absorb solar heat, especially through the near infrared
range (700 nm-2500 nm) of the solar spectrum. This phenomenon is
increased as the granules covering the surface become dark in
color. For example, while white-colored asphalt shingles can have
solar reflectance in the range of 25-35%, dark-colored asphalt
shingles can have solar reflectance of only 5-15%. Furthermore,
except in the white or very light colors, there is typically only a
very small amount of pigment in the color coating of the
conventional granules that reflects solar radiation well. As a
result, it is common to measure temperatures as high as 77.degree.
C. on the surface of black roofing shingles on a sunny day with
21.degree. C. ambient temperature. Absorption of solar heat may
result in elevated temperatures at the shingle's surroundings,
which can contribute to the so-called "urban heat-island effect"
and increase the cooling load to its surroundings. This not only
increases the demand for indoor cooling energy, but also
contributes to smog formation due to higher surface temperatures.
Hence, it is beneficial to have a surface with increased solar
reflectance, such as greater than 70 percent, to reduce solar heat
gain, thereby reducing the heat flux entering the building envelope
or reducing surface temperatures for lowering smog formation. It is
therefore advantageous to have roofing shingles that have high
solar reflectance.
[0008] The surface reflectivity of an asphalt shingle largely
depends on the solar reflectance of the granules that are used to
cover the bitumen. Typically, roofing granules are applied such
that about 95 to 97 percent of the shingle surface is effectively
covered by the granules.
[0009] The state of California has implemented a building code
requiring the low-sloped roofs to have roof coverings with solar
reflectance greater than 70%. However, colored roofing granules,
prepared using current coloring technology, are not generally
capable of achieving such a high level of solar reflectance. Thus,
in order to reduce solar heat absorption, it has been suggested to
apply coatings externally directly onto the shingled surface of
roofs. White pigment-containing latex coatings have been proposed
and evaluated by various manufacturers. However, the polymeric
coating applied has only limited amount of service life and
requires re-coat after certain years of service. Also, the cost of
adding such a coating on roof coverings can be relatively high.
Other manufactures have also proposed the use of exterior-grade
coatings that were colored by IR-reflective pigments for deep-tone
colors and sprayed onto the roof in the field. U.S. Pat. No.
7,238,408 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% obtained
by adding metal flakes or metal flakes coated with metal oxides or
sulfides such as titanium dioxide or zinc sulfide. U.S. Pat. No.
6,933,007 discloses the use of novel granules with solar
reflectance greater than 55% and hardness greater than 4 on Moh's
scale to enhance the solar reflectivity of asphalt based roofing
products.
[0010] Solar control films that contain either a thin layer of
metal/metal oxides, or dielectric layers applied through vacuum
deposition, have been commercially available for use in
architectural glasses.
[0011] U.S. Pat. No. 7,273,634 discloses pulverizing recycled
ceramic material such as furnace liner blocks to form a powder and
granular ceramic material to be dispersed in an adhesive and used
for coating roofing shingles.
[0012] Many materials have been proposed for use in protecting
roofing from solar heat radiation, such as ceramic grog, recycled
porcelain (U.S. Pat. No. 6,933,007, incorporated herein by
reference), and white plastic chips. However, the previously
proposed materials have limited use, and cannot satisfy all
requirements for roofing materials.
[0013] There is a continuing need for roofing materials, and
especially asphalt shingles, that have improved resistance to
thermal stresses while providing an attractive appearance. In
particular, there is a need for roofing granules that provide
increased solar heat reflectance to reduce the solar absorption of
the shingle. Hence, it would be advantageous to have a roofing
product that has solar reflectance greater than 70%. It is further
advantageous that such a product could be applied to other
substrates, such as siding or paving, or can be constructed as part
of the system exposed to solar radiation such that the solar heat
gain can be reduced to mitigate the urban heat island effect.
SUMMARY OF THE INVENTION
[0014] The present invention provides synthetic roofing granules
that provide increased solar heat reflectance, as well as a process
for preparing such roofing granules, bituminous roofing products
incorporating such roofing granules, and a process for preparing
such roofing products. In one aspect, synthetic roofing granules
according to the present invention comprise at least one sintered
aluminosilicate having a crystalline content of at least ten
percent, more preferably at least 70 percent, and still more
preferably at least 90 percent. In one embodiment, the synthetic
roofing granules comprise sintered bauxite; and in another
embodiment, the synthetic roofing granules comprise sintered kaolin
clay.
[0015] The present invention thus provides a process for preparing
roofing granules. The process includes providing a ceramic-forming
material comprising at least one aluminosilicate and forming the
ceramic-forming material into green granules. The process further
comprises sintering the green granules at a temperature of at least
900 degrees Celsius to cure the green granules until the
crystalline content of the sintered granules is at least ten
percent as determined by x-ray diffraction, and more preferably, at
least about 90 percent. The conditions selected for sintering
depend on the identity of the ceramic-forming material. In one
aspect of the present invention, the ceramic-forming material is
kaolin clay. In another aspect of the present invention, the
ceramic-forming material is bauxite.
[0016] When the ceramic-forming material is kaolin clay, the green
granules are preferably sintered at a temperature of at least 1450
degrees Celsius until the crystalline content of the granules is at
least about 90 percent, and more preferably about 100 percent, as
determined by x-ray diffraction. Preferably, when the
ceramic-forming material is kaolin clay, the granules are sintered
until the granules consist essentially of a mixture of at least one
aluminosilicate, preferably mullite and/or sillimanite,
crystoballite and quartz. In this case, ceramic-forming material
can further include a mineral material, such as titanium
dioxide.
[0017] When the ceramic-forming material is bauxite, the green
granules are preferably sintered at a temperature of at least 1250
degrees Celsius until the crystalline content of the granules is at
least about 10 percent, and more preferably about 70 percent, as
determined by x-ray diffraction. Preferably, when the
ceramic-forming material is bauxite, the granules are sintered
until the granules consist essentially of a mixture of at least one
aluminosilicate, preferably mullite and/or sillimanite,
crystoballite, quartz and corundum. In this case, ceramic-forming
material can further include a mineral material, preferably
titanium dioxide.
[0018] Preferably, the amorphous material content of the sintered
granules is greater than about five percent.
[0019] Preferably, the sintered granules contain less than three
percent crystalline silica, more preferably, less than one percent
crystalline silica.
[0020] In one presently preferred embodiment of the process of the
present invention, the ceramic-forming material is mixed with a
liquid to form a mixture, the mixture is formed into pellets, such
as spherical pellets, and the pellets are screened to provide green
granules having a predetermined initial particle-size distribution.
The green granules are subsequently sintered to provide a mixture
of sintered granules. In this embodiment, the process of the
present invention can further include embedding sintered granules
in a bituminous surface. Two or more lots of sintered granules
having different predetermined initial particle-size distributions
can be combined to provide a mixture of sintered granules having
predetermined final particle-size distribution, such as a bimodal
particle-size distribution. Preferably, the predetermined final
particle-size distribution and the particle shape are selected to
maximize coverage of the shingle surface by the sintered granules.
Preferably, the predetermined final particle-size distribution is
selected to provide at least 85 percent surface coverage when the
sintered granules are embedded in a bituminous surface, more
preferably at least 90 percent, and still more preferably at least
97 percent. The sintered granules can be embedded in the bituminous
surface by applying a mixture of sintered granules having a
predetermined particle-size distribution to the bituminous surface.
Alternatively, two or more mixtures of sintered granules having
different particle-size distributions can be applied successively
or simultaneously to the bituminous surface. The present invention
also provides roofing granules and bituminous roofing products
prepared according to the process of the present embodiment.
[0021] In another aspect, the present invention provides a process
for forming bituminous roofing products with high solar heat
reflectance, comprising providing a ceramic-forming material
comprising kaolin clay; forming the ceramic-forming material into
green granules; and sintering the green granules at a temperature
of at least 900 degrees Celsius until the crystalline content of
the sintered granules is at least ten percent, as determined by
x-ray diffraction. In this aspect, the process of the present
invention further includes providing a bituminous roofing sheet
material having an upper surface; and applying the sintered
granules in the upper surface of a bituminous roofing sheet
material. The process further preferably includes pressing the
sintered granules into the upper surface of the bituminous roofing
sheet to embed the sintered granules in the upper surface of the
roofing material. In this aspect of the process of the present
invention, the ceramic-forming material is formed into at least two
different classes of green granules, each class of green granule
being characterized by a predetermined average particle size prior
to sintering the green granules, and the green granules are
sintered to provide at least two size classes of sintered granules.
In one presently preferred embodiment, the process further
comprises blending sintered granules from at least two different
size classes prior to applying the sintered granules to the upper
surface of a bituminous sheet roofing material. In another
presently preferred embodiment, the process includes sequentially
applying at least two different classes of sintered granules to the
upper surface of the bituminous sheet roofing material. In one
presently preferred embodiment, the process further includes
applying conventional colored roofing granules in the bituminous
roofing sheet material. In another presently preferred embodiment
the process further includes mixing the sintered granules with a
liquid binder composition prior to applying the sintered granules
to the upper surface of the bituminous roofing sheet material. In
an alternative embodiment, the process further includes applying a
liquid binder composition to the upper surface of the bituminous
roofing sheet material after the sintered granules have been
applied. In either case, the liquid binder composition is
preferably selected from the group consisting of acrylic emulsions,
acrylic solutions, thermoplastic polymers, fluoropolymer emulsions,
epoxy resins, UV curable resins, radiation curable resins, alkaline
metal silicates, sol-gel solutions, silicone resins, and silica
binders. In this aspect, the present process also thus provides a
bituminous roofing product.
[0022] In another presently preferred embodiment, the present
invention provides a process for forming bituminous roofing
products with high solar heat reflectance including providing a
ceramic-forming material comprising at least one aluminosilicate,
and providing base particles comprising material thermally stable
up to a temperature of at least 900 degrees Celsius. The process
further includes applying the ceramic-forming material to the base
particles to form a green coating layer on the base particles to
form green granules and sintering the green granules at a
temperature of at least 900 degrees Celsius until the crystalline
content of the coating layer of the granules is at least ten
percent as determined by x-ray diffraction, more preferably at
least 25 percent, still more preferably at least 50 percent, and
most preferably about 100 percent. The process further preferably
includes providing a bituminous roofing sheet material having an
upper surface and applying the sintered granules in the upper
surface of a bituminous roofing sheet material. Preferably, the
process further comprises pressing the sintered granules into the
upper surface of the bituminous roofing sheet to embed the sintered
granules in the upper surface of the roofing sheet.
[0023] In one aspect, the ceramic-forming material is formed into
at least two different classes of green granules, each class of
green granule being characterized by a predetermined average
particle size, prior to sintering the green granules. The green
granules are sintered to provide at least two size classes of
sintered granules. Preferably, the process further comprises
blending sintered granules from at least two different size classes
prior to applying the sintered granules in the upper surface of the
bituminous sheet roofing material. In one aspect of the present
process, at least two different classes of sintered granules are
applied sequentially into the upper surface of the bituminous
sheet-roofing material. In another aspect of the present process,
the process further comprises applying conventional colored roofing
granules in the bituminous roofing sheet.
[0024] In another aspect of the present invention, the sintered
granules are mixed with a liquid binder composition prior to
applying the sintered granules to the upper surface of the
bituminous roofing sheet material. In an alternative aspect of the
present invention, the process further comprises applying a liquid
binder composition to the upper surface of the bituminous roofing
sheet after the sintered granules have been applied. In either
case, the liquid binder composition is preferably selected from the
group consisting of acrylic emulsions, acrylic solutions,
thermoplastic polymers, fluoropolymer emulsions, epoxy resins, UV
curable resins, radiation curable resins, alkaline metal silicates,
sol-gel solutions, silicone resins, and silica binders. In this
embodiment, the process also preferably provides a bituminous
roofing product.
[0025] In another embodiment, the present invention provides a
process for forming bituminous roofing products with high solar
heat reflectance including providing a ceramic-forming material
comprising at least one aluminosilicate, forming the
ceramic-forming material into green granules, and sintering the
green granules at a temperature of at least 900 degrees Celsius
until the crystalline content of the sintered granules is at least
ten percent as determined by x-ray diffraction. In this embodiment,
the process further includes providing a matrix material for
securing the sintered granules, and forming a solar reflective
sheet comprising sintered granules and matrix material. Preferably,
the process further includes providing a bituminous roofing sheet
material with an upper surface, and applying the solar reflective
sheet to the upper surface of a bituminous roofing sheet material,
to form a bituminous roofing product.
[0026] In yet another embodiment, the present invention provides a
process for forming bituminous roofing products with high solar
heat reflectance comprising providing a ceramic-forming material
comprising at least one aluminosilicate, providing base particles
comprising material thermally stable up to a temperature of at
least 900 degrees Celsius, and applying the ceramic-forming
material to the base particles to form a green coating layer on the
base particles to form green granules. The process further
comprises sintering the green granules at a temperature of at least
900 degrees Celsius until the crystalline content of the sintered
granules is at least ten percent as determined by x-ray
diffraction. The process also includes providing a matrix material
for securing the sintered granules, and forming a solar reflective
sheet comprising sintered granules and matrix material. The process
further optionally includes providing a bituminous roofing sheet
material having an upper surface, and applying the solar reflective
sheet to the upper surface of a bituminous roofing sheet material,
to form a bituminous roofing product.
[0027] In another aspect, the present invention provides a process
for preparing roofing granules comprising providing base particles,
providing a ceramic-forming material comprising at least one
aluminosilicate, coating the base particles with a layer of
ceramic-forming material to form green granules having an exterior
layer, and sintering the green granules at a temperature of at
least 900 degrees Celsius to cure the green granules until the
crystalline content of the exterior layer of the sintered granules
is at least ten percent as determined by x-ray diffraction. In one
aspect of this process, the base particles preferably comprise a
sintered ceramic material formed from at least one aluminosilicate.
Thus, the present invention also provides roofing granules
comprising a base particle, and an exterior coating on the base
particle, the exterior coating comprising a sintered ceramic
material formed from clay and having a crystalline content of at
least ten percent as determined by x-ray diffraction. Preferably,
in one aspect, the roofing granules have base particles comprising
a sintered ceramic material formed from clay.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a schematic illustration of a first embodiment of
a process for preparing a bituminous roofing material with high
solar heat resistance according to the process of the present
invention.
[0029] FIG. 2 is a schematic illustration of a second embodiment of
a process for preparing a bituminous roofing material with high
solar heat resistance according to the process of the present
invention.
[0030] FIG. 3 is a schematic illustration of a roofing granule with
high solar heat resistance according to the present invention.
[0031] FIG. 4 is a graph showing measured solar reflectivity as a
function of particle size for roofing granules prepared according
to the present invention from kaolin clay.
[0032] FIG. 5 is a graph showing measured solar reflectivity and
percent surface area coverage as a function of particle size for
roofing shingles coated with roofing granules prepared according to
the present invention from kaolin clay.
DETAILED DESCRIPTION
[0033] The present invention provides mineral-surfaced roofing
products, including bituminous roofing membranes and shingles, with
high solar reflectance, such as greater than 70 percent, as well as
excellent UV opacity to protect the underlying asphalt substrate,
and excellent outdoor durability for its long-term usage, as well
as good fire resistance and mechanical strength. The present
invention also provides granular roofing materials that exhibit
solar reflectance greater than about 73 percent.
[0034] Bituminous roofing membranes are frequently covered with a
layer of mineral-based roofing granules in order to protect the
underlying bituminous layer from degradative effects of UV
radiation and to provide an attractive appearance. In addition,
roofing granules can help reduce cooling loads by reflecting solar
heat. Typically, the applied layer of roofing granules does not
completely cover the bituminous surface. Approximately 3 to 5
percent of the surface remains exposed in bituminous roofing
membranes produced by a typical manufacturing process. Thus, in
order to provide roofing products with at least 70 percent solar
reflectance, solar heat-reflective granules having a solar
reflectance of greater than about 73 percent are required, such as
are provided by the present invention.
[0035] As used in the present specification and claims, "near
infrared-reflective" and "solar heat-reflective" refer to
reflectance in the near infrared range (700 to 2500 nanometers) of
the electromagnetic spectrum. "Visible" refers to the visible range
of the electromagnetic spectrum (400 to 700 nm). "Ultraviolet" and
"UV" refer to the ultraviolet range (10 to 400 nanometers) of the
electromagnetic spectrum. As used in the present specification and
claims, the "opacity" of an object or medium refers to the
extinction of incident radiation by the object or medium and is the
sum of the absorption of incident radiation and the scattering of
incident radiation. As used in the present specification and
claims, "about" means plus or minus three percent or less. As used
in the present specification and claims, "encapsulate" means to
cover completely, that is, to cover 100 percent of the surface.
[0036] As used in the present specification and claims, "granule
coloring pigment" denotes a conventional metal oxide-type pigment
employed to color roofing granules. As used in the present
specification and claims, the strength in color space E* is defined
as E*=(L*.sup.2+a*.sup.2+b*.sup.2).sup.1/2, where L*, a*, and b*
are the color measurements for a given sample using the 1976 CIE
L*a*b* color space. The total color difference .DELTA.E* is defined
as
.DELTA.E*=(.DELTA.L*.sup.2+.DELTA.a*.sup.2+.DELTA.b*.sup.2).sup.1/2
where .DELTA.L*, .DELTA.a*, and .DELTA.b* are respectively the
differences in L*, a* and b* for two different color
measurements.
[0037] By "aluminosilicate" is meant a mineral comprising aluminum,
silicon and oxygen, including: (a) aluminum silicates such as
naturally occurring minerals such as adalusite, kyanite, and
siimanite, having the composition Al.sub.2SiO.sub.5, (b) layered
hydrous aluminum silicates such as kaolinite,
Al.sub.2Sl.sub.2O.sub.5(OH).sub.4, halloysite
Al.sub.2(Si.sub.2O.sub.5)(OH).sub.4.2H.sub.2O, pyrophyllite
Al.sub.2(Si.sub.2O.sub.5).sub.2(OH).sub.2, montmorilonite
(Al.sub.1.67Na.sub.0.33Mg.sub.0.33)(Si.sub.2O.sub.5).sub.2(OH).sub.2,
mica AL.sub.2K(Si.sub.1.5Al.sub.0.5O.sub.5).sub.2(OH).sub.2, and
illite
Al.sub.2-xMg.sub.xK(Si.sub.1.5-yAl.sub.0.5+yO.sub.5).sub.2(OH).sub.2,
(c) clays including layered hydrous aluminum silicates such as
kaolin clays; (d) bauxites including the minerals gibbsite
Al(OH).sub.3, boehmite gamma-AlO(OH), and/or diaspore
alpha-AlO(OH); and (e) feldspars such as orthoclase, [(K,
Na)AlSi.sub.3O.sub.5].sub.4, albite [NaAlSi.sub.3O.sub.8].sub.4,
and anorthite, Ca[Al.sub.2Si.sub.2O.sub.8].
[0038] By "kaolin clay" or "kaolin" is meant a material comprising
kaolinite, quartz and feldspar. For use in the process of the
present invention, it is preferred that kaolin clay have a
kaolinite content of at least about 80 weight percent, more
preferably at least about 90 weight percent, and still more
preferably at least about 95 weight percent.
[0039] By the "sphericity" of a three-dimensional particle is meant
the ratio of particle volume to that of the smallest circumscribing
sphere.
[0040] By "spherical" particle is meant a particle having an
average ratio of minimum dimension to maximum dimension of 0.7 or
greater, or having an average sphericity value (ratio of the
surface area of a sphere (with the same volume as the given
particle) to the surface area of the particle) of about 0.7 or
greater.
[0041] By "sintering" is meant a method for making objects from
powdered material, by heating the material from below its melting
point (solid state sintering) until the particles adhere to each
other.
[0042] By "calcining" is meant heating a solid material such as an
ore to a temperature below the melting point and sintering point of
the solid material in order to bring about a thermal decomposition,
phase transition, or removal of a volatile fraction.
[0043] By "mesh size" is meant ASTM U.S. Standard mesh size unless
otherwise indicated.
[0044] By "crystalline content" is meant the proportion, on a
weight basis, of anhydrous crystalline material, as opposed to
crystalline material including physically adsorbed and/or
chemically bound water, as determined by x-ray diffraction. Thus,
crystalline materials, such as kaolinite, gibbsite, bohemite, etc.,
which include physically adsorbed and/or chemically bound water,
are excluded, and crystalline materials which do not include
physically adsorbed or chemically bound water, such as mullite and
corundum, are included.
[0045] Unless otherwise stated, "percent" or "percentage" refers to
the percent by weight.
[0046] By "granule surface coverage" is meant the percent of roof
membrane surface area covered by roofing granules as measured using
image analysis software, such as Image-Pro Plus from Media
Cybernetics, Inc., Silver Spring, Md. 20910. The shingle surface
area is recorded as a black and white image using a CCD camera
fitted to a microscope. The image is then separated into an
asphalt-coating portion and a granule covering portion using the
threshold method in gray scale. The amount of granule coverage is
then calculated by the image analysis software based upon the
number of pixels with gray scale above the threshold level divided
by the total number of pixels in the image.
[0047] By "solar reflectivity" and "solar heat reflectance" is
meant the quantity measured by a solar spectrum reflectometer
(Model SSR available from Devices and Services Inc., Dallas, Tex.),
unless otherwise indicated.
[0048] Preferably, the present invention provides highly solar
heat-reflective, solid, durable, and crush-resistant materials
suitable for roofing applications including particles with sizes
ranging from -12 U.S. mesh to +50 U.S. mesh and granules with sizes
ranging from -10 to +40 U.S. mesh.
[0049] Referring now to the drawings, in which like reference
numerals refer to like elements in each of the several views, there
are shown in FIG. 1 a schematic illustration of a first embodiment
of a process 10 for preparing a bituminous roofing material with
high solar heat resistance according to the process of the present
invention. An aluminosilicate such as a Tertiary or Cretaceous
kaolin clay is subjected to a series of conventional operations 12
to beneficiate the clay, including blunging, degritting,
classifying, magnetically separating, flocculating, filtrating,
redispersing, spray drying, pulverizing and calcining.
Subsequently, the beneficiated clay is mixed 14 with a suitable
binder, such as polyvinyl alcohol, and the mixture is delivered to
an intensive mixer, such as an Eirich mixer, where the binder and
clay mixture is formed 16 into generally spherical "green" or
uncured granules or particles. The resulting green granules or
particles are then dried 18 and then classified 20 by dropping them
through a series of screens of varying mesh sizes. The classified
green granules are then sintered 22 by heating them in a suitable
kiln or oven at a temperature of at least about 900 degrees Celsius
so that a crystalline phase having high solar heat reflectance
formed. The classified sintered granules are then mixed 24 to form
a blend of a desired particle-size distribution, such as a
particle-size distribution tending to maximize surface coverage
when the blend is applied to the upper surface of a bituminous
sheet roofing product. The sintered granule blend is then applied
26 to the heat-softened upper surface of a bituminous roofing sheet
product by conventional means, such as dropping at a metered
application rate from an overhead hopper. Subsequently, the
granules are pressed 28 into the upper surface of the bituminous
roofing sheet product using a pressure roll. The bituminous roofing
sheet product is then cooled and cut into roofing shingles, which
are subsequently packaged.
[0050] FIG. 2 is a schematic illustration of a second embodiment of
a process 30 for preparing a bituminous roofing material with high
solar heat resistance according to the present invention. An
aluminosilicate such as kaolin clay is subjected to a series of
beneficiating operations 32 to form a dried, calcined powder.
Subsequently, the beneficiated clay is mixed 34 with a suitable
binder, such as starches such as potato starch, synthetic binders
such as polyvinyl alcohol or liquid binders such as AR animal glue,
to form a coating composition. The coating composition is applied
36 to crushed, classified stone particles in a suitable mixing
apparatus to form a green coating on the granules. The coating
operation is repeated using at least two batches stone particles
having different average particle sizes to yield classified green
granules. The stone particles can be classified 38 by dropping them
through screens of differing mesh sizes. The resulting green
granules or particles are then dried 40. The classified green
granules are then sintered 42 by heating them in a suitable kiln or
oven at a temperature of at least about 900 degrees Celsius so that
a crystalline phase having high solar heat reflectance is formed.
The classified sintered granules are then mixed 44 to form a blend
having a desired particle-size distribution, such as a
particle-size distribution tending to maximize surface coverage
when the blend is applied to the upper surface of a bituminous
roofing sheet product. The sintered granule blend is then applied
46 to the heat-softened upper surface of a bituminous roofing sheet
product by conventional means, such as dropping at a metered
application rate from an overhead hopper. Subsequently, the
granules are pressed 48 into the upper surface of the bituminous
roofing sheet product using a pressure roll. The bituminous roofing
sheet product is then cooled, and cut 50 into roofing shingles,
which are subsequently packaged.
[0051] FIG. 3 is a schematic side sectional view of a roofing
granule produced according to the process of FIG. 2. The granule 60
includes an interior core 62 of a stone dust particle 64. The
interior core 62 is covered with an exterior layer 66 of sintered
kaolin particles 68. The sintered kaolin particles 66 largely
comprise mullite with a small amount of crystoballite, and have
high crystallinity as determined by x-ray diffraction and
concomitant solar heat reflectance.
[0052] The highly solar heat-reflective materials of the present
invention are preferably prepared by heating suitably sized
ceramic-forming material comprising at least one aluminosilicate
such as kaolin clay at temperatures from 900 degrees Celsius to
1450 degrees Celsius. The at least one aluminosilicate is
preferably sintered at the elevated temperature, and the
crystalline content, as determined by x-ray diffraction, increases
from about ten percent, when the ceramic-forming material is
sintered at 900 degrees Celsius, to about 100 percent, when the
ceramic-forming material is sintered at 1450 degrees Celsius. While
not intending to be bound by any particular theory, it is believed
that when the at least one aluminosilicate is kaolin clay, the
kaolin clay undergoes an almost linear thermal expansion as it is
heated up to about 600 degrees Celsius, at which point the volume
declines due to dehydration. At about 900 degrees Celsius a phase
transition to an intermediate spinel crystalline phase is believed
to occur. At about 1200 degrees Celsius, it is believed that a
further phase transition begins to occur, with the intermediate
spinel phase being transformed into a crystalline mullite phase and
a glassy silica phase or crystalline cristobalite phase, depending
on the rate at which the material is being heated, to yield a
completely sintered material at about 1500 degrees Celsius.
Preferably, the ceramic-forming material is heated at a rate
favoring the formation of the crystalline cristobalite phase. For
example, a heating rate of less than about 20 degrees Celsius per
minute is preferred.
[0053] The aluminosilicate preferably used in the process of the
present invention can be a clay material such as a kaolin clay. The
kaolin clay preferably used in the process of the present invention
can be a kaolin crude material, including kaolin particles,
oversize material, and ferruginous and/or titaniferous and/or other
impurities, having particles ranging in size from submicron to
greater than 20 micrometers in size. Alternatively, a refined grade
of kaolin clay can be employed, such as, for example, a grade of
kaolin clay including mechanically delaminated kaolin particles.
Further, grades of kaolin such as those coarse grades used to
extend and fill paper pulp and those refined grades used to coat
paper can be employed in the process of the present invention.
[0054] In addition to the at least one aluminosilicate such as
kaolin clay, the ceramic-forming material can include small amounts
of other minerals. For example, the ceramic-forming material can
include small amounts of other minerals selected to further
increase the solar heat reflectance of the sintered ceramic-forming
material. In particular, small amounts of microcrystalline silica,
such as novaculite, can be mixed with kaolin clay to form the
ceramic-forming material. By "small amounts" is meant less than
about five percent by weight. Further, small amounts of titanium
dioxide can be mixed with kaolin clay to form the ceramic-forming
material, although the presence of titanium dioxide in the sintered
ceramic-forming material is not essential to achieving high solar
heat-reflectance. Small amounts of titanium dioxide are also
present in some kaolin clays as mined. Preferably, the
ceramic-forming material includes less than three percent
crystalline silica, more preferably, less than one percent
crystalline silica.
[0055] Processes which can be used or adapted for use in preparing
the synthetic roofing granules of the present invention include
processes for preparing synthetic proppant materials, such as
processes for preparing high strength proppants from clay, and
mixtures of clay with other materials, such as disclosed, for
example, in U.S. Pat. Nos. 4,251,265, 4,668,645, 4,555,493,
4,921,820, 5,120,455, and 7,036,591, each of which is incorporated
herein by reference. Other useful processes include processes for
producing high strength proppants from bauxite, such as are
disclosed, for example, in U.S. Pat. Nos. 4,440,866, 4,639,427,
4,712,203, 4,879,181, 5,175,133, each of which is incorporated
herein by reference. Still other useful processes include processes
for preparing high strength proppants from composite materials,
such as disclosed, for example, in U.S. Pat. Nos. 4,944,905,
6,753,299, 6,983,797, and 7,678,723, each of which is incorporated
herein by reference.
[0056] Highly solar heat-reflective materials of the present
invention can be prepared by the processes disclosed in U.S. Pat.
No. 6,780,804, incorporated herein by reference.
[0057] The ceramic-forming material comprises at least one
aluminosilicate, and can include uncalcined, partially calcined, or
calcined clay, preferably kaolin clay. Examples of other
ceramic-forming materials that can be employed in the process of
the present invention include bauxite clays, including low iron
bauxites, kaolinitic clays such as china clays, ball clays,
fireclays, and flint clays, Dover clay, bauxite clays, diaspore
clay, burley clay, mixtures thereof, and mixtures thereof with
kaolin clay. Further, kaolin clay blended with other
aluminosilicate species can also be employed. For example, blends
of kaolin clay and bauxite can be used. Kaolinitic clays are
preferred. Examples of ceramic-forming materials that can be used
include sillimanite minerals (63% Al.sub.2O.sub.3 and 37%
SiO.sub.2) which form ceramics having similar composition, as well
as bauxite, preferably, bauxite having a low level of iron oxide or
hematite. Clays employed in the present process can be beneficiated
by flotation, selective flocculation, magnetic separation,
degritting, delamination, leaching, and like processes. Further,
mixtures of one or more aluminosilicates and other mineral species
such as nepheline syenite can be employed.
[0058] Preferably, the at least one aluminosilicate,
ceramic-forming material, provides a ceramic having a composition
of from about nine parts by weight Al.sub.2O.sub.3 to one part by
weight SiO.sub.2 to about one part by weight Al.sub.2O.sub.3 to
nine parts by weight SiO.sub.2. In addition, the at least one
aluminosilicate, ceramic-forming material, can include
Fe.sub.2O.sub.3 such that the resulting ceramic includes up to
about ten percent by weight Fe.sub.2O.sub.3. Preferably, however,
the iron oxide content of the resulting ceramic is less than three
percent by weight.
[0059] Preferably, the at least one aluminosilicate,
ceramic-forming material, is selected so that the roofing granules
produced by the process of the present invention have an alumina
content of greater than 50 percent, an amorphous material content
of greater than five percent, and a crystalline silica content of
less than three percent, more preferably, less than one
percent.
[0060] The at least one aluminosilicate, ceramic-forming material,
can also include a small amount of one or more mineral materials
that act as sinter aids or fluxes during the sintering process.
Thus, the ceramic-forming material can include one or more
sintering aids such as bentonite clay, iron oxide, boron, boron
carbide, aluminum diboride, boron nitride, boron phosphide, other
boron compounds, and/or fluxes, such as sodium carbonate, lithium
carbonate, feldspar, manganese oxide, titania, iron oxide, or
sodium silicates.
[0061] In one presently preferred embodiment of the present
invention, a starting material comprising particles of the at least
one aluminosilicate, ceramic-forming material, are agglomerated
into green granules. The green granules are subsequently sintered
to provide roofing granules. If desired, a binder such as a starch,
a resin, a wax, gelatinized cornstarch, calcium carbonate,
polyvinyl alcohol, or combination thereof, can be added to improve
pelletizing and to increase the green strength of the unsintered
granules. Generally the binder is added at about 0-6% by weight,
based on the weight of ceramic-forming material.
[0062] The starting material is preferably ground, such as by ball
milling or another attrition process, to form particles having a
mean size of about 20 microns or less, more preferably about 15
microns or less, most preferably, about 10 microns or less,
expressed in terms of the particle diameter (or average particle
size, where the particles are non-spherical). Depending on the
attrition process employed, the starting material can be dried to
improve the ease of grinding, if desired.
[0063] If desired, a binder for example, a starch, resin or wax,
such as gelatinized cornstarch, calcium carbonate, polyvinyl
alcohol, or combination thereof, may be added to the ground
starting material mixture to improve pelletizing and to increase
the green strength of the unsintered granules.
[0064] In a presently preferred embodiment of the process of the
present invention, the ground starting materials are combined with
a liquid, such as water, and mixed in an intensive mixer having a
rotatable containment vessel provided with a rotor table and a
rotatable impacting impeller, such as an Eirich mixer. The rotor
table, or pan, rotates in an opposite direction to the impacting
impeller. The impacting impeller may be in the form of a disk with
rods or bars attached to the disk and aligned generally parallel
with the axis of rotation of the impeller. Sufficient liquid is
added to cause essentially spherical granules of the mixture to
form. Generally, about 15-40 wt. percent liquid based on the weight
of starting materials is added. After such granules have formed,
from about 0-25 percent, more typically, from about 5 to about 15
wt. percent of additional starting material, which is preferably,
the same dry starting material as is used to form the wet mixture,
is added to the mixture. Addition of this dry powder stops the
granule growth and completes the mixing operation.
[0065] Although an intensive mixer can be used to produce green
granules, other forming methods can also be used. For example, a
slurry of the starting material in water may be sprayed to form the
granules. Spray-drying apparatus and techniques which can be
employed in the process of the present invention are disclosed, for
example, in U.S. Patent Publication 2009/0008805 A1, U.S. Pat. No.
7,067,445, and U.S. Pat. No. 7,387,752, each of which is
incorporated herein by reference, and in Spray Dryers: A Guide to
Performance Evaluation (2d Ed. American Institute of Chemical
Engineers 2004).
[0066] Examples of spray-drying techniques that can be employed
include atomizing a ceramic fluid feedstock into a spray of
droplets, which become dried on contact with hot air. For example,
a slurry of ceramic starting material, such as a mixture of
aluminosilicates which may be calcined, partially calcined, or
uncalcined, and water, and optionally other component such as
binder material, for example, a starch such as potato starch,
polyvinyl alcohol, methylcellulose, dextrin, or the like, and/or
dispersants such as colloidal dispersants, polyelectrolyte
dispersants, pyrophosphates and the like, and/or rheology control
agents, is prepared. The slurry can have a high solids content,
that is, greater than fifty percent by weight. The slurry is pumped
through a pressure nozzle, rotary wheel atomizer, pressurized dual
fluid nozzle, or other suitable device, to atomize the slurry into
droplets, which contact hot air while falling through a drying
chamber, to form dried green particles. The dried green particles
can then be sintered using a suitable sintering furnace.
[0067] Further, while an intensive mixer can be used to produce
spherical green granules, forming methods which provide other
granule geometries (for example ellipsoidal or cylindrical) can
also be employed.
[0068] Granules produced according to the process of the present
invention preferably have a particle size of from -0.8 to -0.9 on
the Krumbein scale.
[0069] Preferably, the granule geometry is selected to maximize
coverage of the bituminous roofing surface in which the granules
are embedded. In particular, granules having a flat or plate-like
geometry are preferred.
[0070] Multiple-size classes of granules can be used to maximize
coverage.
[0071] The resulting green granules are then dried to a moisture
content of less than about 10 weight percent, usually in a drier at
between about 100 degrees C. and about 300 degrees C. The dried,
green granules thus formed are thereafter sintered in a furnace at
a predetermined sintering temperature to provide highly solar
heat-reflective roofing granules.
[0072] The green granules can be screened for size, preferably
after drying. An initial screening of the green granules can be
carried out after drying, but prior to sintering. For example, a
top screen having a mesh size of about 14 or 16 mesh can be used to
screen out the largest particles, and a bottom screen having a mesh
size of about 28, 30, or 32 is used to remove the finer particles.
The choice of top and bottom screens depends, in part, on the
mixture produced by the mixer and can be adjusted to tailor the
median particle size of the mixture. The rejected oversized and
undersized granules may be recycled. A further screening may take
place after sintering.
[0073] Generally, suitable sintering temperatures are generally
about 1200 degrees Celsius and above, more preferably, above about
1300 degrees Celsius, and most preferably, about 1500 degrees
Celsius. Dried green granules consisting of kaolin clay are
preferably sintered at a temperature of at least 900 degrees
Celsius, and preferably between 900 degrees Celsius and about 1450
degrees Celsius, to cure the green granules until the crystalline
content of the sintered granules is at least 10 percent, more
preferably at least 25 percent, still more preferably at least 50
percent, and most preferably about 100 percent, as determined by
x-ray diffraction.
[0074] Sintering results in a change in specific gravity and volume
of the granules. Preferably, the green granules are sintered until
a specific gravity between about 2.1 and 4.2 g/cc is obtained,
depending on the composition of the ceramic-forming mixture being
sintered, and the desired specific gravity of the roofing granules.
For granules formed consisting essentially of kaolin clay, which
comprises about 46 percent by weight Al.sub.2O.sub.3 and about 54
percent by weight SiO.sub.2, the specific gravity after sintering
is preferably from about 2.2 to 2.9 g/cc. In general, the specific
gravity after sintering ranges from about 2.2 to 4.2 g/cc,
depending on the composition of the ceramic-forming material.
Sintering generally causes a reduction of up to about 20% in
granule size as well as an increase in specific gravity of the
granule.
[0075] The finished granules can be spherical (i.e., have an
average sphericity value of about 0.75 or greater, more preferably,
at least 0.80, and typically, 0.80-0.9). The particle size of the
sintered and screened granules is generally between 0.1 and about
2.5 millimeters. The screen sizes can be selected to provide a
granule mixture with a desired, predetermined particle-size
distribution.
[0076] Preferably, the particle-size distribution of the granules
is selected to maximize coverage, and hence protection, of the
bituminous surface in which the granules are embedded. For example,
the granules can be screened to provide at least 85 percent, more
preferably at least 95 percent, and still more preferably at least
97 percent surface coverage, when the roofing granules are embedded
in a bituminous surface. In order to maximize surface coverage, a
bimodal particle-size distribution can be selected. For example, a
first batch of granules having an average particle size of -16/+18
mesh can be prepared, and a second batch of granules having an
average particle size of -35/+40 mesh can be prepared. A granule
mixture can then be prepared by mixing 94 wt. percent of the first
batch of granules with 6 wt. percent of the second batch of
granules. When a bimodal particle-size distribution is selected, it
is preferred that the ratio of the two maxima in the particle-size
distribution be selected to maximize coverage of the bituminous
surface such that the smaller particles tend to fill the
interstices between the larger particles. Thus, the ratio of the
maxima of the smaller size granules to the maxima of the larger
size granules is preferably between about 0.22 and 0.5, which is
alternatively expressed as the ratio of the maxima of the larger
size granules to the smaller size granules of about 4.5 to 2.
[0077] In this embodiment, the process of the present invention
further includes providing a bituminous roofing sheet material
having an upper surface. The preparation of bituminous roofing
sheet material is well known in the art. Typically, bituminous
roofing sheet material comprises a reinforcing web of a fibrous
material, such as for example glass fibers. The reinforcing web is
typically impregnated with a bituminous material at an elevated
temperature and in addition may be coated on one or both sides with
a bituminous material having the same or different composition as
than used to impregnate the web. The sintered granules can be
applied to the upper surface of the bituminous roofing sheet
material, preferably while the bituminous material is sufficiently
soft and deformable (for example, when the temperature of the
bituminous material is greater than about 300 degrees Fahrenheit,
or about 150 degrees Celsius) so that the sintered granules will
strongly adhere to the bituminous material on cooling. If desired,
the sintered granules can be pressed into the upper surface of the
bituminous roofing sheet material in order to securely embed the
sintered granules in the upper surface of the bituminous roofing
sheet material. The surface of the kaolin granules can be treated
with an adhesion promoter, a silicone emulsion, or a mineral oil to
improve the adhesion of the kaolin granules to the bituminous
roofing sheet material.
[0078] In one aspect of the process of the present invention, the
ceramic-forming material is formed into at least two different
classes of green granules, each class of green granule being
characterized by a predetermined average particle size, prior to
sintering the green granules, and the green granules are sintered
to provide at least two size classes of sintered granules. For
example, a first class of granules having a #22 grading (that is, a
class of granules having particle size greater than 70 U.S. mesh
and less than 14 U.S. mesh) can be blended with a second class of
granules having a #28 grading (that is, a class of granules having
particle size greater than 70 U.S. mesh and less than 18 U.S. mesh)
in a weight ratio of 10 percent to 90 percent. Subsequently, the at
least two different classes of sintered granules can be applied
sequentially into the upper surface of the bituminous sheet roofing
material; for example, by being dropped from separate hoppers unto
the upper surface of the bituminous roofing sheet material. For
example, when only two classes of granules are prepared, the larger
of the two classes of granules can be applied first, and the
smaller of the two classes of granules can be applied subsequently
to fill the interstices between the larger granules. The first
class of granules can be optionally pressed into the upper surface
of the bituminous roofing sheet material before the second class of
granules is applied. Alternatively, the granules can be pressed
into the upper surface of the bituminous roofing sheet material
after both classes of granules have been applied. In another
alternative, the smaller of the two classes of granules can be
applied first, and the larger of the two classes of particles can
be applied subsequently. In this case also, the first (smaller)
class of granules can be optionally pressed into the upper surface
of the bituminous roofing sheet material before the second (larger)
class of granules is applied. Preferably, the second class of
granule is pressed into the upper surface of the bituminous roofing
sheet material in this alternative. In another aspect of the
process of the present invention, two or more size classes of
granules having different average particle sizes are mixed together
to form a granule mixture, and the granule mixture is applied to
the upper surface of a bituminous roofing sheet material. The two
classes of granules can be blended, for example, by using a
vibratory feed or in a slate drum, and the blended granules can
then be dropped onto the upper surface of the bituminous roofing
sheet material. The granules are then preferably pressed into the
upper surface of the bituminous roofing sheet material.
[0079] Highly solar heat-reflective roofing granules useful in the
process of the present invention for preparing roofing bituminous
roofing products are available from Saint-Gobain Proppants as
Versaprop, Interprop, and Ultraprop sintered bauxite granules.
[0080] In another aspect of the process of the present invention,
highly solar heat-reflective roofing granules are employed with
other types of roofing granules, such as conventionally colored
roofing granules to enhance the solar reflectance of colored
bituminous roofing sheet materials, and/or with algae resistant
roofing granules, in order to provide resistance to algae growth on
the roofing surface.
[0081] Roofing granules are conventionally colored using metal
oxide coating pigments. Examples of coatings pigments that can be
used include those provided by the Color Division of Ferro
Corporation, 4150 East 56th St., Cleveland, Ohio 44101, and
produced using high temperature calcinations, including PC-9415
Yellow, PC-9416 Yellow, PC-9158 Autumn Gold, PC-9189 Bright Golden
Yellow, V-9186 Iron-Free Chestnut Brown, V-780 Black, V0797 IR
Black, V-9248 Blue, PC-9250 Bright Blue, PC-5686 Turquoise, V-13810
Red, V-12600 Camouflage Green, V12560 IR Green, V-778 IR Black, and
V-799 Black. Further examples of coatings pigments that can be used
include white titanium dioxide pigments provided by Du Pont de
Nemours, P.O. Box 8070, Wilmington, Del. 19880. Such metal oxide
pigments are typically dispersed in a binder comprising a mixture
of an alkali metal silicate, such as aqueous sodium silicate, and
heat reactive aluminosilicate material, such as clay, preferably,
kaolin. The proportion of alkali metal silicate to heat-reactive
aluminosilicate material is preferably from about 3:1 to about 1:3
parts by weight alkali metal silicate to parts by weight
heat-reactive aluminosilicate material, more preferably about 2:1
to about 0.8:1 parts by weight alkali metal silicate to parts by
weight heat-reactive aluminosilicate material. Such conventional
granules are fired at an elevated temperature, such as at least
about 200 degrees Celsius, and preferably about 250 to 500 degrees
Celsius. At the elevated temperature the clay reacts with and
neutralizes the alkali metal silicate, thereby insolubilizing the
binder. The binder resulting from this clay-silicate process,
believed to be a sodium aluminum silicate, is porous, such as
disclosed in U.S. Pat. No. 2,379,358 (incorporated herein by
reference). The alkali metal silicate can be aqueous sodium
silicate solution having a total solids content of from about 38
percent by weight to about 42 percent by weight, and having a ratio
of Na.sub.2O to SiO.sub.2 of from about 1:2 to about 1:3.25.
[0082] Conventionally colored roofing granules can be mixed with
highly solar heat-reflective roofing granules prepared according to
process of the present invention, and the mixture can be applied to
the upper surface of a bituminous roofing sheet product.
Alternatively, the conventionally colored roofing granules and the
highly solar heat-reflective roofing granules can be applied
sequentially to the upper surface of a bituminous roofing sheet
product. For example, conventional colored roofing granules can be
applied first to the upper surface of a bituminous roofing sheet
material followed by application of the highly solar
heat-reflective roofing granules of the present invention.
[0083] Thus, in one aspect of the present invention, the solar
reflectance of conventional roofing granules is enhanced by mixing
the highly solar heat-reflective granules of the present invention
with conventional roofing granules. The proportion of highly solar
heat-reflective granules to conventional factors can be adjusted
depending on a number of factors, such as the desired appearance of
the resulting mixture, and the desired level of enhancement of
solar reflectance for the mixture. Preferably, the weight ratio of
highly solar heat-reflective granules to conventional granules is
at least 1 to 9, more preferably at least 1 to 4, and still more
preferably 1 to 3.
[0084] In addition to applying the sintered, highly solar
heat-reflective granules according to the present invention
directly to the upper surface of a bituminous roofing sheet
material, other methods can be employed to enhance the solar heat
reflectance of bituminous roofing sheet material with the sintered,
highly solar heat-reflective granules of the present invention.
[0085] For example, in another embodiment of the present invention,
sintered, highly solar heat-reflective, granules according to the
present invention are mixed with a liquid binder composition prior
to applying the sintered granules to the upper surface of the
bituminous roofing sheet material. The mixture of the granules and
liquid binder can be applied to the surface of the bituminous
roofing sheet material using various techniques such as roller
application, roll coating, form application, spraying, flood
coating, etc. The liquid binder composition can be selected to
provide adhesion between the granules and the upper surface of the
bituminous roofing sheet material. In the alternative, a liquid
binder composition can be first applied to the upper surface of the
bituminous roofing sheet material to adhere the sintered granules
to the upper surface of the bituminous roofing sheet material, and
the sintered granules can be subsequently applied. In another
alternative, the sintered granules can be first applied to the
upper surface of the bituminous roofing sheet material, and a
liquid binder composition can be subsequently applied to adhere the
sintered granules to the upper surface of the bituminous roofing
sheet material. The binder composition can be subsequently dried
and/or cured on the surface of the bituminous roofing sheet
material by application of heat, ultrasonic energy, UV radiation or
the like, depending on the composition and functionality of the
liquid binder composition.
[0086] Suitable liquid binder compositions include acrylic
emulsions, latex, thermoplastic polymers, fluoropolymer emulsions,
epoxies, UV or radiation curable resins, alkaline metal silicates,
sol-gel solutions, silicone resins, and silica binders.
[0087] In another aspect of the present invention, the sintered,
highly solar heat-reflective granules or particles can be dispersed
in a suitable matrix material to form a sheet or web, and the
resultant integrated sheet can be laminated onto a roofing
substrate or adhere to an asphaltic substrate, such as a bituminous
roofing sheet material. A tie layer can be employed to enhance the
adhesion of the granule-containing sheet to the substrate. Suitable
matrix materials may include, but not limited to, those liquid
binders such as acrylic emulsions, latex, thermoplastic polymers,
fluoropolymer emulsions, epoxies, UV or radiation curable resins,
alkaline metal silicates, sol-gel solutions, silicone resins, and
silica binders as mentioned above, as well as EPDM, thermoplastic
elastomers, PVC, PVDF, polyolefins, and combinations thereof.
[0088] In yet another aspect, the present invention provides a
process for forming bituminous roofing products with high solar
heat resistance comprising providing a ceramic-forming material
including at least one aluminosilicate, such as kaolin clay, and
base particles comprising material thermally stable up to a
temperature of at least 900 degrees Celsius, and applying the
ceramic-forming material to the base particles to form green
granules. The at least one aluminosilicate, such as kaolin clay,
can be combined with a suitable binder, additives, or fillers to
form a coating composition with suitable consistency and
subsequently applied to the surface of the base particles. The
aluminosilicate coating composition can be applied by various
methods such as pan coating, spray coating, dip coating, shear
mixing, fluidized bed coating, or spin coating to form a green or
uncured coating layer on the base particles to form "green"
granules. Preferably, the aluminosilicate coating composition is
sufficiently thick to provide effective solar heat-reflectance, and
more particularly, the aluminosilicate coating composition is
preferably applied to form a layer of from about 1 micrometer to
300 micrometers in thickness on the base particles. The resultant
green granules are then sintered at a temperature of at least 900
degrees Celsius until the crystalline content of the coating layer
on the base particles is at least ten percent as determined by
x-ray diffraction, more preferably at least 25 percent, still more
preferably at least 50 percent, and most preferably about 100
percent. The green granules can be sintered in a rotary kiln or the
like, such that the desired solar heat reflectance is obtained.
After sintering, the thickness of the sintered solar
heat-reflective coating is from about 0.5 micrometer to 250
micrometers. The resultant sintered, layered, highly solar
heat-reflective granules can be classified as discussed above to
provide a suitable average particle size and particle-size
distribution. For example, the aluminosilicate, ceramic-forming
material can be formed into at least two different classes of green
granules by selecting two different classes of base particles, each
having a different average particle size. The ceramic-forming
material can then be applied to form a green layer on each of the
classes of base particle to form two classes of green granules,
each class of green granule being characterized by a predetermined
average particle size, prior to sintering the green granules. The
green granules can then be sintered to provide at least two size
classes of sintered granules. The two classes of sintered granules
can then be blended, and the blended sintered granules can be
applied to the upper surface of a bituminous roofing sheet
material, and optionally pressed into the upper surface of the
bituminous roofing sheet material in order to embed the sintered
granules in the upper surface of the bituminous roofing sheet
material, or each class of sintered granule can be applied
sequentially to the upper surface of the bituminous roofing sheet
material. Further, conventional colored roofing granules can be
applied to the bituminous roofing sheet material, either as a blend
with the sintered, layered, highly solar heat-reflective granules
of the present invention, or either before of after the sintered,
layered, highly solar heat-reflective granules are applied.
Similarly, the sintered, layered highly solar heat-reflective
granules can be mixed with a suitable matrix material to form a
sheet or web, and the resultant integrated sheet can be laminated
onto a roofing substrate or adhere to an asphaltic substrate, such
as a bituminous roofing sheet material, as discussed above.
Further, the sintered, layered, highly solar heat-reflective
granules can mixed with a liquid binder composition prior to
applying the sintered granules to the upper surface of the
bituminous roofing sheet material and then applied to the surface
of the bituminous roofing sheet material using various techniques
such as roller application, roll coating, form application,
spraying, flood coating, etc. such as discussed above.
[0089] Various types of stone dust can be employed in the process
of the present invention to prepare base particles. Stone dust is a
natural aggregate produced as a by-product of quarrying, stone
crushing, machining operations, and similar operations. The base
particles can be mineral particles of the type typically used for
making roofing granules, such as talc, slag, limestone, granite,
syenite, diabase, greystone, slate, trap rock, basalt, greenstone,
andesite, porphyry, rhyolite, and greystone, or other naturally
occurring metamorphic rocks, crushed ceramic particles, sands,
gravels, or any particles which are both UV opaque and thermally
stable at temperatures greater than 900 degrees Celsius. Mineral
particles of the type typically used for making roofing granules,
while providing good resistance to UV radiation, generally have low
solar heat reflectance, that is, low reflectance of near infrared
radiation. The base particles can be prepared by comminuting and
screening the material to provide an average size suitable for
roofing granules. Preferably, the base particles have an average
particle size from about 0.1 mm to about 2 mm, preferably about 0.4
mm to about 1.5 mm.
[0090] Alternatively, suitable base particles can be prepared by
comminuting suitable minerals to an average size less than that
suitable for use in roofing granules to thus form small particles,
and subsequently agglomerating these small particles to form base
particles. Base particle binder can be included to provide
mechanical strength to the agglomerated particles forming base
particles. The base particle binder is preferably selected from the
group consisting of silicate, silica, phosphate, titanate,
zirconate, and aluminate binders, and mixtures thereof. In one
aspect, the core binder preferably further comprises an inorganic
material selected from the group consisting of aluminosilicate and
kaolin clay. Formation of the agglomerated mineral particles into
cores can be accomplished as disclosed in United States Patent
Publication 2004/0258835 A1 incorporated herein by reference.
[0091] The solar heat-reflective roofing granules of the present
invention can be employed in the manufacture of roofing products,
such as asphalt shingles and bituminous membranes, using
conventional roofing production processes. 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. One side of the roofing product is typically
coated with mineral granules to provide durability, reflect heat
and solar radiation, and to protect the bituminous binder from
environmental degradation. The near solar heat-reflective roofing
granules of the present invention can be mixed with conventional
roofing granules, and the granule mixture can be embedded in the
surface of such bituminous roofing products using conventional
methods. Alternatively, the solar heat-reflective roofing granules
of the present invention can be substituted for conventional
roofing granules in manufacture of bituminous roofing products.
[0092] Other functional additives, such as colorants, algaecides,
biocides, or nano-TiO.sub.2 can be added to the ceramic-forming
material to provide additional functionalities, such as aesthetics,
biocidal effects, self-cleaning, and or nitrogen oxides
reduction.
[0093] Bituminous roofing products 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 a 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, to
render the sheet self-adhering. In this case the adhesive layer is
preferably covered with a suitable release sheet.
[0094] Roofing granules are then distributed over selected portions
of the top of the sheet, and the bituminous material serves as an
adhesive to bind the roofing granules to the sheet when the
bituminous material has cooled.
[0095] Optionally, the sheet can then 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, 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/or aesthetic effect, and the
finished shingles can be packaged. More complex methods of shingle
construction can also be employed, such as building up multiple
layers of sheet in selected portions of the shingle to provide an
enhanced visual appearance, or to simulate other types of roofing
products.
[0096] In addition, the roofing membrane can be formed into roll
goods for commercial or industrial roofing applications.
[0097] Examples of suitable bituminous membranes for use 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, Pa., for example,
WinterGuard.TM. shingle underlayment, a base sheet which is
impregnated with rubberized asphalt.
[0098] 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
include, but are 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 yarn, stretched yarn, crimped yarn, chenille yarn, and
combinations thereof. The cross-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
tetrafluoroethylene 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.
[0099] 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/m.sup.2, more preferably form about 70 to 120
g/m.sup.2, and still more preferably from about 80 to 100
g/m.sup.2, 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/ft.sup.2) are typically employed. 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 such as
polymeric materials, such as 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.
[0100] In yet another aspect of the present invention, the highly
solar heat-reflective granules of the present invention can be
applied to existing roofing surfaces, in the field, to provide
enhance solar heat-reflectance. In this case, the highly solar
heat-reflective granules are preferably dispersed in a suitable
coatings binder, such as an acrylic aqueous latex material to form
a curable, film-forming coating composition, or roof mastic, which
can be applied to the existing roofing surface by a suitable
technique, such as by spray or mopping the coating composition onto
the surface, and then allowing the coating composition to dry and
cure.
[0101] In order to determine the solar reflectivity of a ceramic
material, two tests methods are employed. One method comprises
measuring solar reflectivity using a solar spectrum reflectometer
as directed by the manufacturer. Another method employs a using a
UV/VIS/NIR spectrometer which calculated solar reflectivity from
experimental spectra.
[0102] The solar reflectance of granule-coated bituminous roofing
materials depends upon several factors. First, the solar
reflectance depends on the composition of the roofing granules
coating the roofing materials. The solar reflectance of the
material comprising the roofing granules can be determined by
forming the material into objects having a generally flat surface,
such as disc-shaped coupons. Solar reflectance tends to be reduced
by surface roughness, so that a smooth surface is preferred in
order to determine a reflectance value characteristic of the
material itself. The solar reflectance of the roofing granules
themselves can also be determined, such as by measuring the solar
reflectance of the surface of loose packed granules. In this case,
the solar reflectance is a function of the material from which the
granules are formed, and the size, shape and surface roughness of
the roofing granules. FIG. 4 is a graph showing measured solar
reflectivity as a function of particle size for roofing granules
prepared according to the present invention from kaolin clay,
showing that solar reflectivity increases as particle size
decreases. The solar reflectance of granule-coated bituminous
roofing material can also be measured. In this case, the solar
reflectance is a function of the material from which the granules
are formed, the shape and surface roughness of the granules, and
the extent to which the surface of the bituminous roofing material
is covered by the granules. FIG. 5 is a graph showing measured
solar reflectivity and percent surface area coverage as a function
of particle size for roofing shingles coated with roofing granules
prepared according to the present invention from kaolin clay.
[0103] 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
[0104] Roofing shingles with high solar reflectance according to
the present invention were simulated by applying particles made
from sintered kaolin clays onto asphalt substrate. These sintered
kaolin clay particles had specific particle sizes and solar
reflectance greater than 70 percent, as shown in Table 1. The
sintered kaolin clay particles are commercially available from
Saint-Gobain Corp., Stow, Ohio under the trade name "LWP proppant."
By blending these particles having a designed grading, one can
create particle blends of various particle sizes to optimize
surface coverage. Examples of various size blends are shown in
Table 2. These blends were then applied onto a 1/16'' thick asphalt
film cast on an aluminum plate (25 mil thickness, available from
Q-Panel) to simulate the shingle making process. The asphalt
shingle panel was made by first casting molten asphalt (Venezuelan
crude source) onto the aluminum panel substrate and pressed to a
uniform 1/16'' thickness film. The asphalt panel was then heated on
a hot plate to a temperature below asphalt melting temperature to
soften the asphalt and the particles with designed size
distribution were then dropped freely onto the surface. The panel
was then removed from the hot plate and the particles were pressed
into the asphalt using a 20 pound steel roller while asphalt was
still soft. Excess particles were shaken off from the panel and the
panel was then allowed to cool to room temperature. The solar
reflectance of the resultant shingle panel was measured using a
solar reflectometer (model SSR available from Devices and Services
Inc., Dallas, Tex.) and the color parameters were determined using
a colorimeter (model Labscan XE, available from Hunter Association
Laboratory, Inc., Reston, Va.) under D65 illumination and
10.degree. observer. The results of these measurements are shown in
Table 3. The results show that very high solar reflectance was
achieved. The results show that a solar reflectance greater than 70
percent can be achieved by selecting a particle-size distribution
to optimize surface coverage.
TABLE-US-00001 TABLE 1 Particle Size, Mean Particle Solar US mesh
Size, pm Reflectance % L* a.sup.t b* +10 mesh size 2000 64 79.76
0.07 12.03 +12 mesh size 1700 64 80.25 0.27 11.46 +14 mesh size
1400 66 80.81 0.29 11.25 +16 mesh size 1180 70 83.04 0.58 11.94 +18
mesh size 1000 73 83.97 0.64 12.36 +20 mesh size 850 72 83.62 0.68
13.2 +25 mesh size 710 75 84.76 0.57 13.14 +30 mesh size 600 75
85.37 0.55 13.7 +35 mesh size 500 77 86.03 0.48 14.35 +4O mesh size
425 79 87.24 0.42 14.79 +45 mesh size 355 80 88.37 0.27 14.61 +50
mesh size 300 81 88.98 0.2 14.54
TABLE-US-00002 TABLE 2 Particle Par- size, ticle Blend Blend Blend
Blend Blend Blend Blend Blend US size A B C D E F G H mesh (um) wt
% wt % wt % wt % wt % wt % wt % wt % 10 mesh 2000 0 0 0 I2 mesh
1700 7 7 3 10 2 1 0 14 mesh 1400 18 8 16 mesh 1180 41 23 34 44 8 15
8 7 18 mesh 1000 17.3 22 20 mesh 850 30.3 13 29 30 35 25 35 25 25
mesh 710 9.4 12 30 mesh 600 17.1 7.7 24 14 49 8 40 40 35 mesh 500
2.6 4 40 mesh 425 3.6 1 8 2 8 2 12 23 45 mesh 355 0.5 1 50 mesh 300
1 0.5 2 0 1 4 5 subtotal 100 100 100 100 100 100 100 100
TABLE-US-00003 TABLE 3 Solar Sample Info Reflectance L* a* b*
shingle panel/blend A 57.0% 78.35 -0.17 9.41 shingle panel/blend B
60.0% 80.23 -0.53 8.82 shingle panel/blend C 60.0% 80.33 -0.17 9.49
shingle panel/blend D 63.0% 82.2 -0.42 9.47 shingle panel/blend E
59.0% 79.43 -0.56 9.04 shingle panel/blend F 60.5% 79.82 -0.19 8.68
shingle panel/blend 0 60.0% 80.13 -0.49 8.3 shingle panel/blend H
59.2% 80.31 -0.56 8.42
Example 2
[0105] Highly solar-heat-reflective roofing granules are made by
coating crushed metamorphic rock particles (#11 grading base rock,
available from CertainTeed Corp., Gads Hill, Mo.) with kaolin clay
and subsequently sintered the coating at 1250.degree. C. The
coating process was carried out by first mixing 12 lb of the base
rock with 109 gm of starch as dry binder in an Eirich mixer (model
RVO2E, available from Eirich Corp., Gurnee, Ill.) until a uniform
appearance is achieved. 365 gm of wet binder (AR animal glue) was
then introduced into the mixture over an additional 2 minute
period, followed by slow addition of 2 lb kaolin clay containing
0.12% starch. Mixing was continued until a uniform coating formed
on the base rock. The resultant granules were then fired in a
rotary kiln to a sintering temperature of 1250.degree. C. to fuse
the kaolin clay coating. Care was given in order to prevent
agglomeration of the granules. The finished granules have a solar
reflectance of 42% and the color reading of L*=69.09, a*=0.02, and
b*=4.09.
Example 3
[0106] Roofing shingles with high solar reflectance according to
the present invention were simulated by applying particles made
from sintered kaolin clays onto asphalt substrate as in Example 1.
Unimodal sintered kaolin clay particles with specific particle
sizes were prepared by Saint-Gobain Proppants by sieving, and the
particle sizes and particle-size distribution is determined using a
CAMSIZER.RTM. optical particle size analyzer which is manufactured
by Retsch Technology in Germany. The average particles sizes are
reported in terms of US mesh size and microns in Table 3. The solar
reflectance of the monodisperse particles was measured by spreading
a layer of particles having a thickness of about 30 mm and using a
solar reflectometer as in Example 1. The monodisperse particles
were then applied onto an asphalt film cast on an aluminum plate to
simulate the shingle making process as detailed in Example 1.
Coverage of the asphalt film by the granules was determined by
ImagePro digital image analysis using an auto bi-level setting. The
solar reflectance and color parameters of the resultant shingle
panel were measured as in Example 1. The results of these
measurements are shown in Table 4. The results show that as the
average particle size decreases the solar reflectance increases,
presumably because the particles are packing more effectively to
cover the surface.
TABLE-US-00004 TABLE 4 Particle Par- SR SR Size ticle par- in as-
Cov- US size ticle phalt er- Panel Mesh micron only panel L* a b*
age DD1- 10 2000 64% 46.8% 72.78 -0.04 8.85 67 78C DD1- 12 1700 64%
51.6% 72.98 0.08 8.57 68.62 78D DD1- 16 1180 70% 54.9% 76.68 0 8.59
73.19 78E DD1- 20 850 72% 56.3% 78.09 -0.06 9.31 73.93 78F DD1- 30
600 75% 55.2% 78.04 -0.46 8.59 72.48 78G DD1- 40 425 79% 54.8%
78.45 -0.86 8.11 72.98 78H DD1- 50 300 81% 52.6% 78.06 -1.04 6.7
71.92 78I
Example 4
[0107] Roofing shingles with high solar reflectance according to
the present invention were simulated by applying particles made
from sintered kaolin clays onto asphalt substrate as in Example 1.
Bimodal sintered kaolin clay particles mixtures were prepared by
mixing unimodal kaolin clay particles having the particles sizes
and in the weight ratio shown in Table 5. The bimodal particles
were then applied onto an asphalt film cast on an aluminum plate to
simulate the shingle making process as detailed in Example 1. The
particle-size distribution of one sample (MS9-98D), was created to
match the size distribution of a byproduct of a commercial proppant
production process by sieving and mixing, as shown in Table 6.
[0108] The solar reflectance and color parameters of the resultant
shingle panel were measured as in Example 1. The results of these
measurements are shown in Table 5. The results show that solar
reflectance can be increased by selected the components of a
bimodal particle size mixture of particles, presumably because the
particles can be packed more effectively to cover the surface.
TABLE-US-00005 TABLE 5 Solar Particle Particle Wt. Reflec- Panel
size size ratio L* a* b* tance MS9-98A -18/+20 -40/+45 66% 80.58
-0.6 8.65 0.587 mesh mesh to 34% MS9-98B -16/+18 -35/+40 66% 80.1
-0.5 8.7 0.596 mesh mesh to 34% MS9-98C -14/+16 -30/+40 66% 80.23
-0.6 8.81 0.601 mesh mesh to 34% MS9-98D distribution from 81.3
0.41 9.12 0.611 side products
TABLE-US-00006 TABLE 6 Pass Retain Sieve (-) Sieve (+) (wt.
percent) (wt. percent) #12 #14 0.61 #14 #16 100 11.12 #16 #18 99.97
38.3 #18 #20 99.23 33.93 #20 #25 90.2 3.02 #25 #30 60.49 0.04 #30
#35 32.75 0.55 #35 #40 9.67 3.36 #40 #45 1 5.96 #45 #50 0.05 2.19
#50 #60 0 0.53 #60 #70 0 0.09 #70 #80 0 0.01 #80 #100 0 0.01 #100
#120 0 0 #120 PAN 0 0
[0109] 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 and spirit of the
invention and defined by the appended claims.
* * * * *