DESC:FORM 2

THE PATENTS ACT, 1970 (39 of 1970)

As amended by the Patents (Amendment) Act, 2005 &
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2016 COMPLETE SPECIFICATION
(See section 10 and rule 13)

TITLE OF THE INVENTION

INFRARED REFLECTIVE COATING COMPOSITION

APPLICANT

BOROSIL RENEWABLES LIMITED of 1101, Crescenzo, G-Block, Opposite MCA Club, Bandra Kurla Complex, Bandra (E), Mumbai-400051, Maharashtra, India, an Indian company

PREAMBLE TO THE DESCRIPTION

The following specification particularly describes the nature of this invention and
the manner in which it is to be performed:
TECHNICAL FIELD

The present disclosure relates to an infrared reflective coating composition and a

process for preparing the same.

BACKGROUND

Solar energy that reaches the earth includes wavelengths of about 300 nanometers (nm) to about 2500 nm. About 5% of this energy is in the ultraviolet range (about
300 nm to about 400 nm). About 46% of the total energy of the sun is in the visible

spectrum (about 400 nm to about 780 nm), and the remaining about 49% is in the infrared range (about 780 nm to about 2500 nm). Radiation in this region may be invisible but can still be perceived as heat. Untreated glass is typically transparent to infrared radiation, and consequently infrared radiation from sunlight transmitted
through a window may result in significant heat gain within a building or other

enclosure. Additionally, ultraviolet radiation may also penetrate a glass window and may be converted to infrared radiation within the enclosure due to greenhouse effects. In order to maintain room habitability, cooling systems, such as HVAC systems, may be used to counter the increased heat due to the infrared radiation
build-up. In regions with high insulation, significant costs may be associated with

air conditioning required to counteract the amount of room heat derived from window-transmitted solar energy.

Frequently, darkly tinted, or reflective glass coatings have been used to block the incoming infrared radiation. However, such coatings may substantially reduce the amount of normal visible light, and may, therefore, alter or distort the outside view by a room's occupants. Further, a pigment having infrared reflective capability may,
in nature, reflect visible-light as well. The selection of pigments in coloring may

also be very limited. For example, a coloring pigment with less infrared absorption needs to be selected. Furthermore, a dark color system such as black in particular may reduce infrared reflectance because of its low content ratio of titanium dioxide in a pigment. Therefore, these technologies currently cannot be used for
applications requiring sophisticated designs such as automobiles, buildings, or

photovoltaic applications. To meet the requirements for these uses, there have been demands for an infrared-reflective coating having both high infrared reflectivity and high visible-light transparency.

U.S. Pat. No. 4,293,732 discloses a solar cell construction having a body formed

essentially of silicon and having a surface with a photovoltaic junction applied thereon. An anti-reflection coating (single or multilayer) is formed on the surface. The anti-reflection coating described here is a conventional type, i.e. made of a single layer of a low index material such as magnesium fluoride.

US Pat. No. 5,449,413 discloses solar cell covers comprising a substrate that transmits the spectral region to which the solar cell responds and a multilayer infrared-reflecting coating which incorporates means for suppressing low order

reflections. The multilayer coating reflects spectral band which are adjacent to short and long wavelength limit of the spectral response of the cell.

Particularly in the context of photovoltaic applications, it has been observed that

every 1°C increase in temperature of the solar glass reduces the output by 0.4 %.

This happens mainly in the infrared region (and beyond) when the heat from this region increases the temperature of the solar cell, thereby reducing the output of the solar cell. Accordingly, the solar panel needs to be appropriately coated with a suitable coating composition which could selectively reflect the infrared radiation
without affecting the transmissivity of the visible light.

Moreover, the spectral response of commercially available solar cells today is only from 380 nm to 1100 nm or so, even though work is on to make them responsive to 300 nm to 1200 nm using various technologies including multi junction. In view of
this, IR radiation does nothing but reduces the output of the solar module by heating

it up.

Therefore, there is required a coating composition which selectively reflects the infrared rays to prevent excessive heating and simultaneously provides for an
acceptable visible light transmissivity.

DESCRIPTION OF THE INVENTION

An aspect of the present disclosure relates to an infrared reflective coating composition. In an embodiment, the composition of the present disclosure comprises:
(a) at least one metal compound,

(b) at least one insulator/dielectric compound, and

(c) at least one solvent.

In one embodiment of the invention, the metal compound comprises at least one

metal selected from, but not limited to, gold (Au), silver (Ag), aluminum (Al),

copper (Cu), tungsten (W), and alloys thereof. In another embodiment, these metals may be present in the composition as chlorides, nitrates, sulfates, sulfides, trihydrates, tetrahydrates, complexes and other salts.

In yet another embodiment, the metal compound can be selected from tungsten

hexacarbonyl, copper sulfate pentahydrate, silver nitrate, hydrogen tetrachloroaurate, aluminum chloride, and mixtures thereof.

In an embodiment, the metal compound is present in the composition in an amount

in between 1 wt.% to 40 wt.% based on the total weight of the composition.

In another embodiment, the insulator/dielectric compound is selected from, but not limited to, titanium dioxide, zinc sulfide, zinc oxide, silica, and mixtures thereof. In an embodiment, the insulator compound is a particulate inorganic material, preferably of nano particle size.

In one embodiment, the insulator compound is present in the composition in an

amount in between 1 wt.% to 40 wt.% based on the total weight of the composition.

In yet another embodiment, the solvent in the composition is selected from, but not limited to, water, alcohol, and mixtures thereof. Suitable alcohols include, but are not limited to, methanol, ethanol, isopropyl alcohol, and mixtures thereof.

In an embodiment, the solvent is present in the composition in an amount in between 60 wt.% to 95 wt.% based on the total weight of the composition.

In an embodiment, the composition is a sol-gel composition with solvent as a carrier

and metal compound and insulator compound as solute or gel.

In another embodiment, the composition is applied on the solar glass with a thickness between 10 – 100 nm. As a matter of fact, these thicknesses can be estimated to be ?/4 or close to ?/2, wherein ? is the wavelength of incoming solar
light.

In an embodiment, the solar glass can be coated with the composition using any suitable method. For instance, the solar glass of any suitable dimension can be dip coated with the composition or with the individual components until the required thickness is achieved.

In another embodiment, the composition may also include suitable additives. A

non-limiting list of coating additive base is summarized in Table 1:

Table 1; List of coating additive base for broad application of different coatings,

1 Gold 10 Palladium
2 Silver 11 Silicon di oxide
3 Chrome 12 Magnesium fluoride
4 Copper 13 Cerium fluoride
5 Nickel 14 Hafnium oxide
6 Tantalum 15 Aluminum oxide
7 Aluminum 16 Titanium dioxide
8 Titanium 17 Tantalum oxide
9 Platinum 18 Zirconium oxide

Another aspect of the present disclosure relates to a process for preparing the

infrared reflective coating composition.

In an embodiment, the process is a roller coating process, such as a reverse roll coating process. Reverse-roll coating is a roll to roll coating method for wet coating
having two reverse-running nips. The metering roll and the applicator roll contra- rotate, with an accurate gap therebetween. In the continuation dry samples to pass through tempering furnace.

In another embodiment, the coating process is dip coating where the glass is dipped

into a bath containing the sol-gel solution, as described herein, and gradually lifted at a predetermined speed of for e.g. 25 mm per sec to ensure that the coating composition is applied uniformly over the substrate. The coated glass is then tempered to cure the coating composition on to the substrate.

In yet another embodiment, the coating process uses magnetron where the substrate is placed in a vacuum chamber as anode and the cathodes are made of the coating composition, as described herein. The coating composition is applied on the substrate(glass).

In still another embodiment, the process requires vapour deposition of the coating composition over the glass substrate, which is subsequently cured and tempered.

In one embodiment, the process comprises at least the following steps:

(A) mixing the metal compound, the insulator/dielectric compound, and the solvent
in a furnace at room temperature, and
(B) heating the furnace at a temperature ranging between 100°C to 600°C for a duration ranging between 0.1 h to 2 h.

Advantageously, the present invention composition can be used for coating solar glass, preferably low iron textured, sheet and float glass, and normal flat glass as well.

The coating composition has the following advantages:

- selectively reflects the infrared rays (> 1100nm and upto 2500 nm) to prevent excessive heating,
- increases the output of solar panel even in hot climate,

- increases the life of solar panel,

- the coating composition can also be applied on other glasses, such as but

not limited to, glasses used in automotive applications, or buildings and the likes.
- less consumption of energy and low pollution in the environment by reducing the amount of CFC and CO2 released by air conditioners

EXAMPLE

The following example is illustrative of the invention but not limitative of the scope thereof:

Several compositions were prepared in accordance with the present invention as

summarized in Table 2 below.

Table 2: Infrared reflective coating compositions

Various coating compositions were prepared in the different ratios of metal and dielectric and insulator material as provided in the below table.

Example %
ZnO Cu Al Ag Au SiO2 TiO2
1 50 50
2 100
3 100
4 100
5 100
6 67 33
7 50 50
8 67 33
9 33 67
10 50 50
11 50 50
12 50 50
13 50 50
14 14 86
15 33 67
16 33 67
17 27.5 72.5
18 67 33
19 50 50
20 33 67

Table 3:

The Table 3 below shows different concentration of various metal compound and the dielectric/insulator compound combinations with 1st, 2nd, and 3rd coating on the substrate at different time intervals. IR Coating liquid can be water based or alcohol based containing synthetic nanoparticles of metals and dielectric materials.

Concentration %
Concn in gm per
200 ml Sample No Coating Liquid
coating Coating on top surface
(by dipping in methanol,ethanol or isopropyl alcohol based liquid)
Dielectric Metal

0.5

0.5

1
SiO2 /TiO2/ZnO

1st
10 minutes

Cu/Al/Ag/Au

2nd
10 minutes

SiO2 /TiO2/ZnO

3rd
10 minutes

2
SiO2 /TiO2/ZnO

1st
20 minutes

Cu/Al/Ag/
Au

2nd
20 minutes

SiO2 /TiO2/ZnO

3rd
20 minutes

3
SiO2 /TiO2/ZnO

1st
30 minutes

Cu/Al/Ag/Au

2nd
30 minutes

SiO2 /TiO2/ZnO

3rd
30 minutes

4 Cu/Al/Ag/Au
1st
45 minutes

SiO2 /TiO2/ZnO

2nd
45 minutes

SiO2 /TiO2/ZnO

3rd
45 minutes

1

1

5
SiO2 /TiO2/ZnO

1st
10 minutes

Cu/Al/Ag/Au

2nd
10 minutes

SiO2 /TiO2/ZnO

3rd
10 minutes

6
SiO2 /TiO2/ZnO

1st
20 minutes

Cu/Al/Ag/Au

2nd
20 minutes

SiO2 /TiO2/ZnO

3rd
20 minutes

7
SiO2 /TiO2/ZnO

1st
30 minutes

Cu/Al/Ag/Au

2nd
30 minutes

SiO2 /TiO2/ZnO

3rd
30 minutes

8
SiO2 /TiO2/ZnO

1st
45 minutes

Cu/Al/Ag/Au

2nd
45 minutes

SiO2 /TiO2/ZnO

3rd
45 minutes

9
SiO2 /TiO2/ZnO

1st
10 minutes

Cu/Al/Ag/Au

2nd
10 minutes

SiO2 /TiO2/ZnO

3rd
10 minutes

2

2

10
SiO2 /TiO2/ZnO

1st
20 minutes

Cu/Al/Ag/Au

2nd
20 minutes

SiO2 /TiO2/ZnO

3rd
20 minutes

11
SiO2 /TiO2/ZnO

1st
30 minutes

Cu/Al/Ag/Au

2nd
30 minutes

SiO2 /TiO2/ZnO

3rd
30 minutes

12
SiO2 /TiO2/ZnO

1st
45 minutes

Cu/Al/Ag/Au

2nd
45 minutes

SiO2 /TiO2/ZnO

3rd
45 minutes

3

3

13
SiO2 /TiO2/ZnO

1st
10 minutes

Cu/Al/Ag/Au

2nd
10 minutes

SiO2 /TiO2/ZnO

3rd
10 minutes

14
SiO2 /TiO2/ZnO

1st
20 minutes

Cu/Al/Ag/Au

2nd
20 minutes

SiO2 /TiO2/ZnO

3rd
20 minutes

15
SiO2 /TiO2/ZnO
1st
30 minutes

Cu/Al/Ag/Au

2nd
30 minutes

SiO2 /TiO2/ZnO

3rd
30 minutes

16
SiO2 /TiO2/ZnO

1st
45 minutes

Cu/Al/Ag/Au

2nd
45 minutes

SiO2 /TiO2/ZnO

3rd
45 minutes

Table 4:

Table 4 depicts the Reflectance reading for wavelength in the range of 350 – 2500 nm of nine of the samples from Table 3 against untreated glass:

Samples 380 – 2500
BLANK 7.54
SAMPLE_1R-ALC-diel/metal 8.01
SAMPLE_2R-ALC-diel/metal 7.89
SAMPLE_3R-ALC-diel/metal 8.39
SAMPLE_4R-ALC-diel/metal 7.96
SAMPLE_5R-ALC-diel/metal 7.67
SAMPLE_6R-ALC-diel/metal 7.86
SAMPLE_7R-ALC-diel/metal 8.08
SAMPLE_8R-ALC-diel/metal 8.21
SAMPLE_9R-ALC-diel/metal 7.76

The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since the modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to the person skilled in the art, the invention should be construed to include everything within the scope of the disclosure. ,CLAIMS:We Claim:

1. An infrared reflective coating composition comprising
(a) a layer of at least one metal compound;
(b) a layer of at least one dielectric compound; and
(c) at least one solvent.
2. The infrared reflective coating composition as claimed in claim 1, wherein the at least one metal compound is selected from gold (Au), silver (Ag), aluminum (Al),
copper (Cu), tungsten (W) and alloys thereof.
3. The infrared reflective coating composition as claimed in claim 2, wherein these metals are present in salt form as chlorides, nitrates, sulfates, sulfides, trihydrates, tetrahydrates, complexes.
4. The infrared reflective coating composition as claimed in claim 3, wherein the metal compound is selected from tungsten hexacarbonyl, copper sulfate pentahydrate, silver nitrate, hydrogen tetrachloroaurate, aluminum chloride and mixtures thereof.
5. The infrared reflective coating composition as claimed in claim 1, wherein the metal compound is present in the composition in an amount between 1 wt.% to 40 wt.% based on the total weight of the composition.
6. The infrared reflective coating composition as claimed in claim 1, wherein the dielectric compound is selected from titanium dioxide, zinc sulfide, zinc oxide, silica, and mixtures thereof.
7. The infrared reflective coating composition as claimed in claim 1, wherein the compound is of nanoparticle size.
8. The infrared reflective coating composition as claimed in claim 6, wherein the dielectric compound is present in the composition in an amount between 1 wt.% to 40 wt.% based on the total weight of the composition.
9. The infrared reflective coating composition as claimed in claim 1, wherein the solvent is selected from water, alcohols, and mixtures thereof.
10. The infrared reflective coating composition as claimed in claim 9, wherein the solvent is present in the composition in an amount between 60 wt.% to 95 wt.% based on the total weight of the composition.
11. The infrared reflective coating composition as claimed in claim 1, wherein the composition further comprises additives.
12. The infrared reflective coating composition as claimed in claim 1, wherein the coating is applied on solar glass with a thickness in between 10-100 nm.
13. The infrared reflective coating composition as claimed in claim 1, wherein the composition selectively reflects the infrared rays of wavelength in the range up to 2500 nm.