FORM 2
THE PATENTS ACT 1970
(Act 39 of 70)
COMPLETE SPECIFICATION
(See Section10)
TITLE OF INVENTION:
DARK COLORED COOL ROOF COATINGS
APPLICANT:
Name : INDIAN INSTITUTE OF TECHNOLOGY BOMBAY
Nationality : INDIA
Address : Indian Institute of Technology Bombay, Powai, Mumbai- 400076,
Maharashtra, India.
The following specification particularly describes the invention and the manner in
which it is to be performed.
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DARK COLORED COOL ROOF COATINGS
TECHNICAL FIELD
[0001] The present invention relates to a dark colored cool roof coating
system more particularly relates to a heat reflective coating. The heat reflective
coating comprises colored pigments that provide an excellent solar reflective
property to the coating system.
BACKGROUND
[0002] In residential buildings, commercial spaces and other buildings
temperature of the enclosed space increases during the hot sunny days. For this
reason, outside surface of buildings and roofs are coated or painted with insulating
materials, thereby improving heat shielding effect. The insulating material for
roofing purposes are commercially available in many forms such as asphalt
shingles, bituminous roofing products and laminated shingles, membranes.
[0003] Further the conventional cool roof coatings available today provide
a uniform solar reflectance across the roof surface. These cool roofs normally
appear as white or light colored when viewed from typical vantage points, these
cool roofs have limited adoption. Research studies on solar reflectance of different
roofing materials show a strong correlation between the solar reflectance and
surface temperature in sunlight.
SUMMARY
[0004] According to the present disclosure, a dark colored cool roof
coating system provides the properties of both insulation and high solar
reflectance. The dark colored cool roof coating system comprises a roofing
substrate and a heat reflective coating formed by applying a coating composition
on the roofing substrate. The coating composition comprises a single layer
forming a non-white coating layer on the roofing substrate. The single layer of
coating composition comprises at least one colored near infrared reflecting
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pigment having a spinel-type crystal structure and a filler material added to the
colored near infrared reflecting pigment to increase the insulation. The dark
colored cool roof coating system has a minimum solar reflectance of at least 65
percent.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The detailed description is described with reference to the
accompanying figures.
[0006] Figure 1, illustrates a dark colored cool roof coating system in
accordance with an exemplary embodiment of the present disclosure.
[0007] Figure 2, illustrates a comparison of the high reflective coating of
the dark colored cool roof coating system with a conventional coating system.
[0008] Figure 3, illustrates a graph representing the back panel substrate
temperature of the dark colored cool roof coating system for a constant incident
temperature.
DETAILED DESCRIPTION
[0009] The present disclosure provides a dark colored roof coating system
with a heat reflective coating to provide a minimized heat transfer to the substrate
by reflecting near infrared wavelength portions from the sunlight. The heat
reflective coating comprising colored near infrared pigments exhibiting high solar
reflective property. Insulating filler materials are also incorporated to further
minimize the heat transfer to the substrate.
[0010] Figure 1 illustrates a dark colored cool roof coating system in
accordance with an exemplary embodiment of the present disclosure. The dark
colored cool roofing system 100 comprises a roofing substrate 110. The roofing
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substrate 110 may be concrete, tiles, shingle, marble, a fibrous material or a
bituminous coating with a fibrous material. The roofing substrate has an upper
surface and a lower surface. A heat reflective coating 112 may be formed by
applying a coating composition on the roofing substrate 110. The coating
composition comprises a single layer providing both insulation and solar
reflective properties. The single layer of the coating composition comprises of at
least one colored near infrared reflecting (NIR) pigment 120, having a spinel-type
structure. The resulted coating composition forms a non-white coating layer on
the roofing substrate 110. The non-white layer may be dark in color. The colored
near infrared reflecting pigment may be a mixed metal oxide pigment. In one
embodiment the colored near infrared reflecting pigment comprises at least Ti-Cr-
Sb mixed with metal oxides. The colored near infrared reflecting pigment has a
solar reflectance of at least 65 percent. Furthermore, the colored near infrared
reflecting pigment is contained in an amount of not less than 20% by weight of
the coating composition. The thickness of the colored near infrared reflecting
pigment is about 120 micrometers.
[0011] The non-white layer configuration in accordance with the present
disclosure provides a dark color high reflective coating. The coating composition
of the high reflective coating 112 may be formed in various dark colors. The color
of the high reflective coating 112 depends on the colored near infrared reflecting
pigment used. In one embodiment of the present disclosure, a black colored near
infrared reflecting pigment is used for the coating composition. Other dark
colored near infrared reflecting pigments with colors such as brown, green, blue,
yellow also can be used in the present disclosure. It may be appreciated that the
color of the near infrared reflecting pigment is based on the application
requirement.
[0012] The coating composition also comprises a filler material 130 added
to the colored near infrared reflecting (NIR) pigment 120 to increase the
insulation property of the heat reflective coating 112. The filler material 130 is
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bonded together with the colored near infrared reflecting (NIR) pigment 120 and
to the roofing substrate 110. The filler material 130 comprises of fine size calcium
metasilicate particles. The fillers/additives are added to the coating composition to
improve critical performance characteristics, such as abrasion resistance,
hardness, refractive index, and brightness.
[0013] The dark colored cool roof coating system made in accordance
with the present disclosure may be of any shape, but preferably such roof coating
system designs are planar in shape. The heat reflective coating 112 is coated on
the upper surface 110 of the roofing substrate in an exemplary embodiment of the
present disclosure. Additional coatings also may be applied on one or both sides
of the roofing substrate 110. However the heat reflective coating 112 is the top
coat on the external side.
[0014] Referring to figure 2, there is shown a comparison of the high
reflective coating of the dark colored cool roofing system 200a with a
conventional coating system 200b. The high reflective coating 112 transfers less
net heat 230 to the roofing substrate 110 than the normal coating 202 for the same
incident sunlight 210. The maximum percentage of incident sunlight including the
near infrared wavelength portions of the light 220, is reflected back due to the
high reflective coating 112 on the roofing substrate 110. The remaining part of the
incident sunlight may generate heat and to be transferred to the roofing substrate
110 through the layers of heat reflective coating 112. Only a part of the generated
heat may be transferred to the roofing substrate 110. The remaining part of the
generated heat may be further reflected by the fillers/additives and/or the base
layer employed. Thus, the present disclosure provides less net heat transferred
from the exterior of the high reflective coating 112 to the roofing substrate 110
than the conventional coating system.
[0015] The dark colored cool roofing was tested and the experimental
results show that major drop in temperatures from the exterior sunlight
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environment of the enclosed space covering with the dark colored cool roofing
system. Referring to figure 3, there is shown a graph representing the back panel
substrate temperature of the dark colored cool roofing system for a constant
incident temperature. The effect of the heat reflective coating made the back panel
substrate temperature to 44 degree Celsius for an incident temperature of 80
degree Celsius.
[0016] The heat reflective coating is provided in a thickness effective to
render a solid coating against near infrared light portion of the sunlight, such as a
coating thickness of at least about 200 micrometers. However, the present
disclosure can be realized with the advantageous properties in the colored near
infrared reflecting pigment of thickness about at least 80 micrometers to 120
micrometers. The colored near infrared reflecting pigmented coating comprises a
dry film. Further, when a plurality of coating layers employed, each coating layer
has a thickness of at least about 40 micrometers.
[0017] The solar reflectance of the heat reflective coating of the present
disclosure may be determined by various factors comprising type and
concentration of colored near infrared pigment(s) used in the coating composition
of heat reflective coating. In this single layer coating system, variation in
parameters such as nature of insulating materials, type and concentration of
fillers/additives, number of coating layers employed, thickness of each coating
layer, and the size and shape of the roofing substrate have been examined and
optimized formulations have been obtained for application.
[0018] The present disclosure provides high performance cool roof
coatings with reduced maintenance requirements. With high reflective coating
composition of the present disclosure, the temperature of the roofing substrate
reduces by at least an about 6 degree to 18 degree Celsius. Such reduction in
temperature requires only less power for cooling for the enclosed room/space such
as air-conditioning the room or incorporating the coolers, and leads to high power
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savings. Also, with the less maintenance requirements, the present disclosure also
provides a low cost coating solution and beneficial over the conventional high
cost white cool roof coatings. Furthermore, present disclosure also offers the dark
colored cool roofing system with a variety of color options for the variety of
applications.
[0019] Although the present disclosure has been described in the context
of certain aspects and embodiments, it will be understood by those skilled in the
art that the present disclosure extends beyond the specific embodiments to
alternative embodiments and/or uses of the disclosure and obvious
implementations and equivalents thereof. Thus, it is intended that the scope of the
present disclosure described herein should not be limited by the disclosed aspects
and embodiments above.
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I/WE CLAIM:
1. A cool roof coating system, comprising:
a roofing substrate; and
a heat reflective coating formed by applying a coating composition on the
roofing substrate, said coating composition comprises a single layer forming a
non-white coating layer on the roofing substrate, wherein the single layer
comprising:
at least one colored near infrared reflecting pigment having a
spinel-type crystal structure;
a filler material is added to the colored near infrared reflecting
pigment to increase insulation;
wherein the dark colored cool roof coating system has a minimum solar
reflectance of at least 65%.
2. The cool roof coating system as claimed in claim 1, wherein the roofing
substrate is selected from a group comprising concrete, tiles, shingle, marble, a
fibrous material, or a bituminous coating with a fibrous material.
3. The cool roofing system as claimed in claim 1, wherein the at least one
colored near infrared reflecting pigment has a thickness about 80 micrometers
to 120 micrometers.
4. The cool roofing system as claimed in claim 1, wherein the at least one
colored near infrared reflecting pigment is contained in an amount of not less
than 20% by weight.
5. The cool roofing system as claimed in claim 1, wherein the filler material is
Calcium Metasilicate.
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6. The cool roofing system as claimed in claim 1, wherein said heat reflective
coating is coated on a upper side of the roofing substrate.
7. The cool roofing system as claimed in claim 1, wherein the at least one
colored near infrared reflecting pigment is a mixed with a metal oxide
pigment.
8. The cool roofing system as claimed in claim 1, wherein the at least one
colored near infrared reflecting pigment is selected from the group consisting
of a black colored near infrared reflecting pigment, a brown colored near
infrared reflecting pigment, a green colored near infrared reflecting pigment,
or a combination thereof.
9. The cool roofing system as claimed in claim 1, wherein the at least one
colored near infrared reflecting pigment is selected from the group consisting
of a yellow colored near infrared reflecting pigment, a blue colored near
infrared reflecting pigment, a red colored near infrared reflecting pigment, or a
combination thereof.