I

Field of the Invention

The invention relates to a super hydrophobic coating, with an excellent optical property (transmittance/ reflectance), weather, UV and corrosion resistance properties, process for producing and applying the same on a
S substrate. Said process provides the preparation of coatings of various compositions and different methods of applying or coating the substrates with low curing temperature. Said coatings result in an efficient barrier against dust, weather, corrosion, UV, thermal shock and oxidation. Furthermore, it is an economical process, particularly to apply on solar
10 devices (e.g. reflective mirrors (Al or glass), PV panels, glass cover plates, solar receiver tubes etc.,) and possible to apply on various other devices/objects ( e.g. optical, displays, light screen, automobile windows, ceramic tiles, concretes, leather, fabrics, metal plates, plastics etc.,)

Background of the invention:

15 There are numerous instances where optically clear articles would be damaged if the articles long exposure to moisture, sun-light and different weather conditions or to be obscured by the deposition of dust or dirt. For example, goggles, face shields, ophthalmic lenses, solar reflective mirrors, PV panels, automobile windows. Especially in the case of solar PV
20 panels, the front surface of a PV module (glass window) must have a high transmission in the wavelengths which can be used by the solar cells in the PV module. For example, silicon solar cells, the top surface must have high transmission of light in the wavelength range of 300 nm to 1200 nm. However in the case of concentrated solar thermal (CSP) application, the
25 use of Al reflectors as in the form of bend (parabolic) or flat structure is of greater advantage because it is easy to design in any shape in addition to its high economical advantage. One of the approaches is to operate the CSP system using cost effective reflectors instead of using expensive one.

2

Reflectors are required with high reflection of light in the wavelength range of 300 nm to 2500 nm.

Further, solar PV panels and solar receiver tubes convert sunlight into electricity. These devices are traditionally mounted outdoors on rooftops or

S in wide open spaces where they can maximize their exposure to sunlight. Unfortunately, this type of outdoor placement of the solar panels, solar receiver tubes and reflectors are subjected to substantially constant weather and moisture exposure. Due to this constant and extended exposure to the devices, solar panels, solar receiver tubes and reflector

10 plates are preferably designed for using many years of stable and reliable operation without failure due to moisture damage or other exposure related damages (e.g. corrosion atmosphere and UV exposure). Even small solar cells used in consumer electronic devices should have rugged environmental protection as these devices are by their nature also

15 generally used outdoors or in areas of sun exposure where they can maximize their electron generating ability.

A general challenge in finding the suitable protecting material for use with said devices (solar panels, solar receiver tubes and reflector plates) is finding one protecting surface that has best-in-class qualities for the

20 multifunctional properties desired in all sorts of environmental protections (dust/dirt, weather, corrosion, UV etc) with good optical properties. There may be some coatings that provide good moisture barrier qualities but are not sufficiently transparent to pass light down to the panel or not sufficiently reflect to light to the receiver tube. Some other coatings may be

25 good at moisture and transparent / reflectance property, but not sufficient to withstand against UV and not having dust /dirt repulsion capability which otherwise may reduce the optical property (transparency / reflectance) of the objects with continuous use.

3

Due to the aforementioned problems, the coating having improved

environmental protection configuration with enhanced optical properties

(Transmission / Reflection) are desired for the top surface of PV panels or

CSP reflectors. But, in practice these coatings are not robust enough to 5 withstand the conditions in which most PV / CSP reflector systems are

used. There are alternative techniques to enhance the surface using multifunctional coatings which have super hydrophobic property with other functional properties like high optical property (Transmission/Reflection), corrosion, weather and UV resistances. However, in this case the dust

10 and dirt is more likely to attach itself to the top surface. In addition to its reflection and transmission properties, the top surface should be impervious to water, should have good impact resistance, should be stable under prolonged UV exposure and should have corrosion and weather resistances. Further, water or water vapor ingress into a PV module/ CSP

15 mirror system will corrode the metal contacts and interconnects, and consequently will dramatically reduce their lifetime.

There are several choices for top surface coatings e.g. single layer, bilayer, multilayer etc. Among these single layer coating, having easy to clean property with high optical, weather, UV and corrosion resistance

20 properties developed by an economic process like wet chemical process is most preferable. However most of the current coatings do not have all the said functional properties all together in one single layer coating suitable for both PV panel and CSP reflector applications.

Further, the super hydrophobic coatings can have high optical property of 25 high reflectance I transmittance, long environmental stability (stability

against weather and corrosion environments), high UV resistance, high mechanical and thermal integrity. Preferred coatings by an economic process are Dip, Spray, Flow, and Brush coatings having a combination of the above mentioned properties. This would be the great choice for the

30 economic power generation by a concentrated solar power (CSP)

4

generated both from PV and solar thermal systems. Because coatings are required in a large area for these systems production of long time stable reflectors or PV panels by an economical process is one of the major ways of reducing the cost of solar electricity production.

5 Numerous patents and articles describe the hydrophobic coatings which significantly function as easy to clean property ("dust repulsion property") produced by wet chemical method. In this connection, a European pant, EP 0818561 discloses the development of coatings on silver reflector coatings and substrate for solar reflector application provides an efficient

10 barrier property against dry oxidation at high temperature. The coating may optionally contain a mixture of oxides such as 5i02, A1203, TiO2, ZrO2 and B203 shows the other functional properties such as high adherence, good mechanical and thermal compatibility. But no information is given with regards to properties like the easy to clean, resistances against

15 corrosion, weather and UV exposures to the coating.

EP 1 287 389 describes a reflector, in particular with a reflector body made up of aluminium or an aluminium alloy. Further it mentioned that reflectors of this type often have restricted lifetime when exposed to outdoor weathering. Moisture in conjunction with UV radiation or 002, SO2

20 or other pollutants leads to reduced reflectance values, and in particular to reduced gloss or reduced total reflection. The intention, with the subject matter described in the document mentioned, was therefore to provide a reflector of which the reflective side is resistant to weathering and to corrosion, and also resistant to mechanical influences, which can be

25 cleaned effectively. Further, it discloses that an external final transparent protective layer provided with a thickness of more than 1 pm having roughness (Ra <0.1 pm) developed by sol-gel method from a polysiloxane compound would give a solution for the mentioned problems. The polysiloxane compound was produced from an alcoholic silane solution

30 and an aqueous colloidal silica solution. However, this poly siloxane type

5

of coating doesn't have any additional property of dust/dirt repulsion characteristics of easy to clean property.

Another European patent, EP 0658525 describes the preparation of a water-repellent multilayer film involving the preparation of three different

s layers describes the preparation of three different sol solutions which are then mixed and applied to a glass substrate forming a gel coating on the glass surface. After heating the gel coating layer turns to a superficial metal oxide layer. To this metal oxide layer is further applied a fluoroalkylsilane coating for super hydrophobic property. But it doesn't deal

10 any stability against the aforementioned problems.

U.S. Pat. No. 6,291,070, discloses a method for producing nanostructured moulded articles and layers by means of a wet chemical process comprising a free flowing composition containing solid nano-scaled inorganic particles having polymerizable and/or polycondensable organic

is hydrophobic surface groups. Further it discloses that the coating layers are scratch resistant and may be having other functional properties of antireflective, hydrophilic, hydrophobic, corrosion resistance and antistatic layers. But there is no experimental observation regarding hydrophobic or hydrophilic property for the surface. Further, it discloses that the coating is

20 having a refractive index close to the refractive index of 1.22 on glass substrate. The antireflection layer reduces the reflection of light over a broad spectrum (300-lOOOnm) and exhibited abrasion—resistant, maximum up to 3H.

U.S. Pat. No. 2007/0295390 discloses the methods and devices provided 25 for improved environmental protection for photovoltaic devices and

assemblies. The encapsulated solar cell includes at least one protective layer coupled to at least one surface of the solar cell and the protective layer may be formed from a substantially inorganic material. The protective layer has a chemical composition that prevents moisture from entering the

6

solar cell and wherein light passes through the protective layer to reach an absorber layer in the solar cell. Further, it discloses that the protective layer comprises of silicone based hard coat material or polyacrylate hardcoat containing silica nanoparticles which may be a UV curable or

s heat curable. But it doesn't mention the easy to clean (dust/dirt repulsion) property.

US 2013/ 0033773 describes about a reflector for electromagnetic radiation in the wavelength range of lOOnm to 1mm, having high resistance against weather and corrosion effects, comprising a metal

in reflector body having a reflecting surface or a reflector body on which a reflective layer is deposited, and a transparent cover layer made of polysiloxane formed in a sol-gel process. Further it describes, the cover made of a cross-linked polycondensate product of at least one silicic acid ester and at least one cyclic siloxane oligomer type. However, there is no

is information about the easy to clean property of the transparent covering layer or reflective layer.

US Patents 5,736,249; 6,084,020, 6,120,849 and 6,153,304 disclose two layer hydrophobic coating systems having non-sticky, non-fouling and ice phobic properties for the applications on metal and concrete substrates.

20 The first layer is a fluoro-copolymer having good adhesion properties to the substrate and the second layer a siliconic polymer having hydrophobic properties. Further, it discloses that said coating having a surface energy in the range of 18-21 dynes/ cm and contact angles in the range of 9Q0· But no information is given as regards the resistances against corrosion,

25 weather and UV exposures of the coating

US 2010/0119774 discloses a water-repellent, oil-repellent and antifouling antireflection film comprising a plate substrate, fine particles (nanoparticles in the range from 50-200 nm) fused onto a surface of the substrate and a method for manufacturing such an antireflection film on lens and glass

L

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sheet having a surface coated with a water repellent, oil-repellent, and antifouling film for the application of solar energy and display systems.

US 2011/0129662 discloses a invention concerning a substrate coating that is dust —repellent and is easily cleaned by rain washing of adhering

S inorganic or organic dirts. The coating imparts to the glass in the preferred embodiments additionally an antireflective property and is suitable therefore in particular for coating glass that is used in devices for solar energy utilization (e.g. glass plate for covering PV panels and water heating collectors). For producing the coating, the substrate to be coated

10 is immersed in a coating solution and is then pulled from the solution at an appropriate speed. The wet film that remains on the glass surface is dried and subsequently, as needed, is baked at 500CC for increasing the wear resistance. Further it discloses that said coating material comprises of oxidic particles formed by hydrolytic condensation in a size of 5-20 nm,

15 second particles with a diameter in the size range of 80-300nm and using aqueous or organic solvent or mixture of solvents.

DE 298 12 559 discloses a composite material with an aluminum substrate and an optically functional multilayer system applied thereto, on which, in turn, there is an external protective layer. Said protective layer can be

20 composed of silicon dioxide or, in one embodiment, of a composition produced by using a sol-gel process and preferably made of an organically modified inorganic silicate network. The network have been formed with the use of hydrolysable silanes, in particular siloxanes, which produce, via hydrolysis and condensation to give polysiloxane, with elimination of

25 alcohol or water. However, no specific formulation for producing the siloxane is given.

U.S. Pat. No. 7,211,329 discloses the easily cleanable coated product with abrasion resistance made by a process, in which a coating mixture including hydrophobic and / or dirt repellent substances uniformly

8

distributed throughout a hydrolysable network forming gel is applied to a product surface. The gel is preferably an inorganic metal oxide gel made by sol-gel process. The hydrophobic and/or dirt repellent substance, which is a Fluoro silane compound. But it doesn't mention any stability against

5 the aforementioned problems of weather, corrosion and UV environments.

JP 11092175 A describes a process in which a methoxysilane or an ethoxysilane compound containing a fluoro carbon chain is attached to the surfaces of nanoparticles with a diameter of lOOnm. The nano particles modified in this way are then dispersed in an aqueous medium and

10 applied to the surfaces to be coated. The solvent is then removed by curing the thin films. This provides surfaces coated with small hydrophobic particles.

WO 99/64363 describes also a method of preparing a water repellent surface. The process comprises first roughening the surface of the glass

is and removing all metal ions present on the surface. The film is then applied in a known manner to the previously treated surface. The roughening of the surface makes it possible for the water repellent to fill the roughness valleys. It describes only to provide a hydrophobic property to the surface of the material but not the other functional requirements

20 against the aforementioned problems.

DE 695 02671 and W095/24053 describe a display device comprising a display screen provided with a light —absorbing coating comprising a hybrid inorganic—organic material consisting of an inorganic network of 5i02 and other metal oxide. The polymeric chains are intertwined with the

25 inorganic network, thereby forming a hybrid inorganic-organic network. It has been shown, however, that organic components, particularly hydrophobic organic components, such as fluoroalkyls, cannot be incorporated homogenously in such a layer, but that said components primarily adhere to the surface facing away from the carrier layer.

9

US 2009/0233106 discloses a reflective article, having multiple reflective coating. Further it discloses a method of making a reflective article comprises: providing a transparent glass substrate having a first major surface and second major surface and forming a coating stack over at
S least a portion of the substrate. The coating stack comprises a basecoat formed over at least a portion of the second major surface, a primary reflective coating formed over at least a portion of the basecoat, and an inorganic protective coating formed over at least a portion of the primary reflective coating. Further it explains that the protective coating comprises
10 a material selected from silica, alumina, or a mixture of both and has a thickness in the range of 75nm to 120 nm. But there is no information about the easy to clean property of the inorganic protective coating formed over on the primary reflective coating.

US 20110033678 discloses a coating system comprising an antireflective 1~ with UV resistances functionality. It describes that UV radiation has a
deleterious effect on a wide variety of materials/coatings. For example, it can cause yellowing of and /or fading of colours. This is another main issue when the coating being exposed for long duration in the sunlight or artificial UV light, especially coatings/material consists of UV degradable
20 organics. Further, it provides that coating system comprises a UV protective layer mainly applied below the antireflective layer. UV protective layer comprises particles of cerium oxide, titanium oxide, zinc oxide, or combinations of metal oxides.

None of the above described coatings which are having easy to clean 25 property (super hydrophobic property) with high optical property (high
transmittance on glass substrate / high specular reflectance on the reflector substrate, e.g. Al, glass mirrors) additionally having high corrosion, weather and UV resistance properties. In general, the sol-gel. coating material was produced from a polysiloxane which was produced
30 from alcoholic silanes, which produce, via hydrolysis and condensation to

10

give polysiloxane, with elimination of alcohol or water using aqueous acid as a catalyst or polysiloxane mixed with aqueous colloidal solution. However, the coating material derived from an aqueous based polysiloxane may causes to reduce the optical property of the substrate

s which have higher optical property before the coating.

Therefore, it is an objective of the invention to provide a coating material that after application onto a glass or Al reflector or any surface forms a coating whose surface is easier to clean than coatings of the prior art even when they are exposed to high dust by small and finest atmospheric

10 particles with all weather conditions (high humidity or corrosion environments) wherein the coating resulting in the end has high transparency / reflectance, but without reducing the original optical characteristics of the substrate and additionally provide other functional properties of UV, weather, thermal and corrosion resistances etc.

15 The primary object of the present invention is to develop super- hydrophobic coating for an easy to clean functional property with high optical property (transmittance / reflectance).

Another object of the present invention is to provide a high weather, corrosion, thermal and UV stability and a process for depositing such

20 coatings on Al reflector plates, PV panels and cover glass plates.

Hence the present invention addresses some of the drawbacks set forth in the prior art while meeting the above objectives.

Summary of the invention

The present invention provides a coating of super hydrophobic property 25 (easy to clean) with enhanced optical property and environmental

protection for solar devises like Al reflectors, PV panels and cover glass plates/tubes in particular when applied. It should be understood that this invention is generally applicable to any type of reflector plates, PV panels,

11

cover glass plate/tubes whether they are rigid or flexible in nature or the type of material used in the absorber layer. Embodiments of the present invention may be adopted both batch (dip, spray, flow and brush coating methods) and roll to roll manufacturing processes.

5 The super hydrophobic coating with high optical properties having easy to clean property, UV and corrosion resistance properties , adapted to apply on a substrate as single layer of composite sol, according to the invention comprising of:

a) any one type or mixture of metal oxide precursors selected from
10 M(OR)4, MR1(OR)3, MR2(OR)2, MR3(OR), M(OR)3, MR2(OR), MR1(OR), MR3 and br MR4;where M is metal ion, slected from Zr, Si, Sn, Al, La, Nb and Ta; R is alkyl group,selected from methyl, ethyl, propyl, butyl and phenyl; OR is alkoxy group, selected from methoxy, ethoxy, n-propoxy, propoxy, n-butoxy, isopropoxyethoxy, methoxypropoxy, phenoxy, acetoxy,
15 propionyloxy, ethanolamine, diethanolamin, triethanolamin, methacryloxypropyl, acrylat, methyacrylat and acetylaceton.
b) any one or mixture of alkylsilane compounds selected from 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 2-methacryloxyethyltrimethoxysilane,
20 2-acryloxyethyltrimethoxysilane, 3- methacryloxypropyltriethoxysilane,
3- acryloxypropyltriethoxysilane, 2- glycidoxyethyltrimethoxysilane,
3-glycidoxypropyltriethoxysilane and 2-glycidoxyethyltriethoxysilane.
c) any one or mixture of super hydrophobic agent, selected from perfluoroalkyl, perlluorocycloalkyl, polyethoxylated perfluoroalkyl and
25 polyethoxylated perfluorocycloalkyl silane compounds.

d) any one or mixture of low or high boiling organic solvent selected from methanol, ethanol, n-propanol, iso propanol, n-butanol, isobutanol, n pentanol, isopropoxy ethanol, diol and/or polyol.

12

The present invention also provides methods producing and applying the said coating on the devices for easy to clean/ dust repellent (super hydrophobic) property with improved weather, UV and corrosion protection for solar devices such as Al reflector mirrors, PV panels, glass outer

s covers for PV and CSP applications. In one embodiment, the device comprises of an individually encapsulated solar cell (PV panel) or Al reflector plate or glass cover plate including at least one protective layer coupled to at least one surface of the object and wherein light passes through the protective layer to reach an absorber layer either in the solar

10 panel or solar receiver tube. The protective layer has a chemical composition that prevents deposition of dust/dirt with enhanced optical property (transmittance/reflectance). It should be understood that the protective layer described herein can be applied to any type of device/ object (e.g. optical, displays, light screen, automobile windows, ceramic

15 tiles, concretes, leather, fabrics, metal plates, plastics etc.,) and is not limited.

In another embodiment of the present invention, wherein the object includes at least one protective layer applied to at least one surface of the object. The protective layer has chemical compositions that prevent

20 moisture, corrosive vapours of organic and inorganic substances and UV light from entering the objects, wherein light passes through the protective layer to reach an absorber layer.

According to various embodiments under the present invention described herein, any of the following characteristic features may also apply.

25 ~ The protective layer may be comprised of both organic and inorganic materials.

~ The protective layer may be comprised of low temperature heat

curable composition.

13

The protective layer may be a non aqueous or non acid or non alkali homogenous clear composition.

~ The protective layer may include at least one metal oxide precursor, at least one silicone based material, at least one low or higher

S boiling organic solvent or mixture of both, at least one hydrophobic agent and or combinations thereof.

~ The protective layer may have a composition of zirconium (IV) propoxide (Zr(iv)Pr): isopropanol (IPA): isopropoxy ethanol (IPETOH): 3-glycidoxy propyltrimethoxysilane (GPTS):1H, IH, 2H,

10 2H-perfluorodecyltriethoxysilane or I H, 1 H, 2H, 2H-

perfluorooctyltriethoxysilane in the range of ratio 0 to 15: 25 to 75:

5 to 25: 1 to 20: 0.5 to 5: (wt%) and preferably 6.3 : 72.4 :12

7.4:1.83-1.9 (wt%).

~ The protective layer with high optical and with high dust/dirt, 15 weather, corrosion and UV, resistant properties have a thickness in

the range of about SOnm to about 2 pm and have a refractive index value in the range of about 1.46 to about 1.61.

~ The PV panel may be silicon based or may be a CIGS (copper indium-gallium — selenium) based or may be a dye based. The solar

20 PV cover glass may be a soda lime based or may be a fused silica based or may be a borosilicate flat glass/tube. The reflector may be a glass based or Al based plate.

~ The objects used for coatings may be a rigid or may be a flexible type. The protective layer may cover a top surface and all side

25 surfaces of the objects.

~ The protective layer may be a transparent or reflective layer.

~ The protective layer may be a solution deposited protective layer.

14

The protective layer may be deposited by an economic coating process (e.g dip, spray, brush, flow, spin etc.)

~ The protective layer may be a low temperature curable protective layer curing in the range of about 500 C to about 200~ C for I to 24h

5 curing time.

~ The protective layer covered object may have an equal or < or >1% optical property (transmittance/ reflectance) when compared to the unprotected objects. The protective layer may have a water contact angle in the range of about 850 to about 11 ~ The protective layer

10 may have a dust/dirt deposition and moisture penetration rates sufficiently low so that there is substantially no loss in PV panel efficiency or reflectance property of Al/glass reflector based heliostat / parabolic trough when they are exposed for long hours with various conditions (sunny, rainy and winter seasons).

15 ~ The protective layer has good weather and UV resistant properties. The layer withstand long hours (>lOOh) in the weather and UV stability tests carried out at standard test condition.

~ The protective layer has a dust repulsion property with enhanced optical property and a good weather and UV resistant property and

20 additionally provides a high corrosion resistance property. The layer withstand long hours (>lOOh) in salt spray chamber.

A further understanding of the nature and advantages of the present invention should become apparent from the following description of the preferred process and read in conjunction with the accompanying

25 drawings, which illustrate, by way of example, the principles of the invention.

15

Brief description of the drawings and Tables
Fig.1- Cross — sectional view of a coating substrate on which a high optical property of super hydrophobic (easy to clean property) protective layer has been deposited using preferred process under the invention, Here a fine
S thin novel composition of non porous composite oxide layer having super hydrophobic (easy to clean property) with enhanced optical, weather, thermal, UV and corrosion resistant properties has been generated on the surface of Al-reflector plates, glass plates and PV panels.

Fig.2- FE-SEM pictures of super hydrophobic (easy to clean property) io protective layer deposited over on the substrate.

Fig.3 - FE-SEM cross sectional views of super hydrophobic (easy to clean property) protective layer deposited over on the substrate.

Fig.4 -Total reflectance spectra of super hydrophobic (easy to clean property) coating (SHC -1) deposited on Al reflector plates.

15 Fig.5 - Specular reflectance spectra of super hydrophobic (easy to clean property) coating (SHC -1) deposited on Al reflector plates.

Fig.6 - Transmittance spectra of super hydrophobic (easy to clean property) coating (SHC -1) deposited on glass plates.

Fig.7 - Total reflectance spectra of super hydrophobic (easy to clean 20 property) coating (SHC -2) deposited on Al reflector plates.

Fig.8 - Specular reflectance spectra of super hydrophobic (easy to clean property) coating (SHC -2) deposited on Al reflector plates.

Fig. 9- Transmittance spectra of super hydrophobic (easy to clean property) coating (SHC -2) deposited on glass plates.

25 Fig.10 - Image demonstrating the super hydrophobic property (easy to clean property) of coating on Al reflector, glass plate and PV panel.

Fig.1 I - Image demonstrating the super hydrophobic property (easy to clean property) of coating on other substrates.

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Fig. 12- I-V characteristics of super hydrophobic (easy to clean property) (SHC -1) coated and uncoated PV panels deposited by different techniques.

Table 1— Average total and specular reflectance values of super s hydrophobic (easy to clean property) coating (SHC -1) on Al

reflector plates.

Table 2— Average total and specular reflectance values of super hydrophobic (easy to clean property) coating (SHC -2) on Al reflector plates.

10 Table 3 —Transmittance values of super hydrophobic (easy to clean property) coating on glass plates.

Table 4 — Water contact angle values of super hydrophobic (easy to clean property) coatings (SHC -1 and SHC-2) on Al reflector plates.

Table 5 — Water contact angle values of super hydrophobic (easy to clean 15 property) coatings (SHC -1 and SHC-2) on glass plates.

Table 6 — Bend profile test of super hydrophobic (easy to clean property) coating (SHC -1) on Al reflector plates.

Table 7 - Thermal stability of super hydrophobic (easy to clean property) coating (SHC -1) on Al reflector plates.

20 Table 8 — Corrosion stability of super hydrophobic (easy to clean property) coating (SHC -1) on Al reflector plates.

Table 9 — UV and weather stability of super hydrophobic (easy to clean property) coating on Al reflector plates.

Table 10 — Performance of coated (SHC -1) and uncoated PV panels by I 25 V measurement used with AM 1.5 solar simulator (1 000W)

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Table I
SHC-I

Sample % Total reflection % Specular reflection
(300-2500nm) (300-2500nm)
Bare Al mirror 94.9 88.4
Dip coated 95.5 90.0
Brush coated 95.0 83.6
Spray coated 91.4 89.5
Flow coated 92.2 87.7
Table 2
SHC-2
Sample % Total reflection % Specular reflection
(300-2500nm) (300-2500nm)
Bare Al mirror 94.9 88.4
Dip coated 95.0 87.8
Brush coated 95.1 88.4
Spray coated 93.1 88.5
Flow coated 92.4 88.9
10

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5
Table 3
Sample
SHC-1 SHC-2
Bare glass 84.8 84.8
Dip coated 84.6 84.2
Brush coated 85.1 80.4
Spray coated 84.8 78.9
Flow coated 84.9 80.4
Table 4
Water contact angle (degrees)
Sample SHC-1 SHC-2
Bare 54 54
Dip 91 99
Brush 100 93
Spray 92 107
Flow 87 103
19

% Transmittance (300-2500 nm)

5

Table 6

Table 5
Sample
SHC-1 SHC-2
Bare 59 59
Dip coated 107 106
Brush coated 98 98
Spray coated 100 101
Flow coated 105 89
Water contact angle (degrees)

% Total Reflection (300-2500nm)

Sample SHC-1 SHC-2
Before After Before After
Uncoated Al plate 95.21 94.27 95.21 94.27
Dip coated 94.96 94.72 94.98 94.21
Brush coated 95.05 94.30 95.00 93.56
Spray coated 93.19 92.59 93.50 92.25
Flowcoated 92.40 92.11 92.51 92.01
20

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Table 7

% Total Reflection (300-2500nm)

Sample SHC-1 SHC-2
Before After Before After
Uncoated Al plate 95.21 94.01 95.21 94.01
Dip coated 95.00 95.30 95.03 95.29
Brush coated 95.13 95.17 94.89 94.90
Spray coated 93.19 94.53 93.23 94.65
Flow coated 92.45 94.52 92.51 94.25
Table 8:
% Total Reflection (300-2500nm)
Sample SHC-1 SHC-2
Before After Before After
Uncoated Al plate 94.91 93.82 94.91 93.82
Dip coated 94.97 94.72 94.75 94.21
Brush coated 95.08 94.60 95.07 95.04
Spray coated 93.15 92.71 93.15 93.01
Flow coated 92.45 92.51 92.41 92.16
10

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Table 9:

% Total Reflection (300-2500nm)

Sample SHC-I SHC-2
Before After Before After
UncoatedAl plate 94.51 94.11 94.51 94.11
Dip coated 94.91 94.98 94.81 94.61
Brush coated 95.12 94.96 95.06 94.90
Spray coated 93.44 93.21 93.12 93.16
Flow coated 92.56 92.39 92.42 92.35

Table-I 0
Panel RP
(W) Voc lsc Vm
(V) (A) (V) Im (A) Fill Efficiency
Factor (%)
(%)
Un coated 10.32 21.80 0.672 17.57 0.587 70.4 13.47
Flowcoated 10.27 21.78 0.669 17.63 0.552 73.8 13.40
Brush coated 9.68 21.61 0.603 17.31 0.593 70.4 12.70
Spraycoated 10.21 21.69 0.640 17.27 0.570 70.9 12.85
Voc
- Open Circuit Voltage; lsc - Short Circuit Current, Vm - Maximum Voltage; Im - Maximum Current

Detailed description of the invention

Here, we have tried to explain some of the preferred embodiment of the 10 process under the invention with particular reference to the drawings, and

particularly to Fig. 1. The sCiper hydrophobic (easy to clean property) coating with an excellent optical property (transmittance/reflectance), weather, UV and corrosion resistance properties comprise of non porous fluorosilane modified 5i02-ZrO2 based composite layer, which are

15 prepared by a non aqueous, non acid and non base sol-gel process and

22

deposited successfully by a series of cost effective coating techniques, e.g. dip, spray, flow, brush coating techniques.

In a preliminary step of the process, Al reflector plate/ glass plate/ PV panel substrate is cleaned. The bare substrate is cleaned with a mild

S detergent solution and rinsed with tap water followed by deionised water. The cleaned plate is then dried at 50-i 00~ C for 10-15 mm in an air—oven or hair-drier. The Al/ glass plate used in the examples set forth below were square and flat, with dimensions of 100 mm x 100 mm x 3mm (length x width x thickness). Polycrystalline Si based PV panels used in the

10 examples were rectangle with pattern cover glass plate, aluminium frame, with dimensions of 320 mm x 245 mm x 25mm (length width x thickness). However, the process disclosed can easily be used for plates/tubes having either smaller or larger sizes, and for complicated shapes having curvatures and bends.

15 The coating solution for depositing a single layer of super hydrophobic (easy to clean property) coating is a fluorosilane modified 5i02-ZrO2 based composite sol. The prepared hybrid sols are deposited individually on each substrate by using all the cost effective techniques like spray, brush, flow and dip coating process.

20 All the coatings perform in a coating room having controlled humidity. It has been observed that the humidity within coating room must be precisely controlled within the range 40-55% to ensure deposition of transparent defect free coating layers. Similarly, the temperature in the coating room is preferably maintained in the range 20-250C.

25 Following the deposition of coating layer, especially when coatings is applied on Al and glass substrates, they are transferred to an oven, for drying at 50-1000C for 15-30mm, followed curing at 2000C for 1-4hr with 5- 100C /min heating rate. The curing process evaporates residual organics from the coating layer to yield a solid film. However coating applied on the

23

PV panels with aluminium frame and electric circuit board, the coating layer is dried at 50-800C for 30-60mm followed curing at 1000C for 1-24hr with 5-1 00C mm heating rate..

Following the curing of the super hydrophobic (easy to clean) coating, the

s coated Al plates/Glass plates/ PV panels are subjected to several tests.

One test employs a spectrophotometer to evaluate the coated substrate's optical property (either transmittance or reflectance) over the full visible to NIR range (full solar wavelength range of 300-2SOOnm). Water contact angle is measured to verify the super hydrophobic property (easy to clean

10 property) of the coating. Salt spray test, UV and weather stabilities are tested as per ASTM standard test procedures for IOOh (1 17B and GiSS). Other tests are also carried out to ascertain the coating's mechanical and thermal properties, including bend profile, thermal cycle and PV panel performance test.

15 Having described the process of the invention in a general way, now, we will further illustrate on the mode of execution and demonstrate the properties of the invention and its practical advantages with the help of the following examples. Details of the preparation and the characteristic properties of two different super hydrophobic (easy to clean) coatings on

20 Al plates, PV glass cover plate and PV panels for providing high reflective on Al plates or high transmittance on glass plates in a full solar range (300-2SOOnm) with other functional properties weather, UV and corrosion resistance properties are explained here by way of example . These examples are merely illustrative, and should not be construed as limited.

25 Example I

A super hydrophobic (easy to clean property) coatings with an excellent optical property (reflectance / transmittance), weather, UV and corrosion resistance properties, SHC-1 single layer system is developed on the substrate using a low temperature curable fluoro silane modified 5i02-

24

ZrO2 based composite sol for the deposition of single layer system of easy to clean coating. For this hybrid sol preparation, 9.19 g of Zirconium propoxide (70 %) in n-propoanol Zr(n-Pro) was dispersed in 105.2g of isopropyl alcohol (IPA), 17.34g of isopropoxy ethanol (IPE), 10.72 g 3-

s Glycidoxypropyltrimethoxysilane (GPTS) and 2.82g 1H, IH, 2H, 2H perfluorodecyltriethoxysilane. For the 1st mixture of sol preparation, 9.19 g of Zirconium propoxide (70 %) in n-propoanol Zr(n-Pro) was dispersed in 105.2g of isopropyl alcohol (IPA) and 17.34g of isopropoxy ethanol (IPE). In the first step Zirconium propoxide was mixed thoroughly with a mixture

10 of isopropyl alcohol (IPA) and isopropoxy ethanol (IPE) and permitted to age for 1-24h. After ageing of the first mixture, 10.72 g 3- Glycidoxypropyltrimethoxysilane (GPTS) was added slowly with stirring for l5min-lhr and followed ageing for 1-24hr (2nd mixture). After ageing of the 2nd mixture, 1 H, I H, 2H, 2H perfluorodecyltriethoxysilane was added

15 slowly and followed stirring for 15mm -lh, after which the whole mixture was allowed to ageing at room temperature for 1-24hr with stirring. The composition of the mixture sol for the super hydrophobic (easy to clean) single layer was Zirconium propoxide (70 %) in n-propoanol Zr(n-Pro):

isopropyl alcohol (IPA), isopropoxy ethanol (IPE): 3- 20 Glycidoxypropyltrimethoxysilane (GPTS): and 1H, 1H, 2H, 2H

perfluorodecyltriethoxysilane (PFDTS) = in the range of ratio 0 to 15: 25 to 75: 5 to 25: ito 20: 0.5 to 5: (wt%) and preferably 6.3: 72.4:12: 7.4:1.9 (wt%).

The coating sol for the super hydrophobic (easy to clean property) was 25 utilized for the coating of super hydrophobic (easy to clean property) single

layer coating with other multifunctional properties of high optical (high transmittance/ reflectance), high weather, UV and corrosion resistances and other mechanical property and coated the substrate (Al reflector plate/glass plate/PV panel) by using all the cost effective techniques like

30 spray, brush, flow and dip coating process.

25

After coating, the coating on the substrate was found to be clear and super hydrophobic nature.

Thereafter, the substrate with the super hydrophobic (easy to clean property) single layer coated was transferred to an oven and dried first at

5 50-1000C for 15-30mm and followed by curing at 100-2000C for I - 4h with

5-100C /min heating rate for PV cover glass plate or Al reflector substrate. However coating applied on the PV panels with aluminium frame and electric circuit board, the coating layer is dried at 50-800C for 30-60mm followed curing at 1000C for 1-24hr with 5-100C mm heating rate.

10 After the curing step, the single layer of super hydrophobic (easy to clean property) coating from this example was found to be non porous morphological structure (no pores, voids and cracks) (Fig.2). Moreover, the layer is clear, uniform and free of any visible defects. The refractive index and thickness of the coating layers developed by dip, flow, spray

15 and brush coating processes were measured by ellipsometer and FE-SEM and found to be lOOnm, 600 nm, 1.5 pm and 1 pm, respectively (Fig. 3). The refractive index of the layer was measured and found to be in the range 1.46 — 1.52 (at a wavelength of 546 nm). The coating's reflectance on the Al reflector and the coating transmittance on the glass plates were

20 measured using a spectrophotometer over a broad solar wavelength range of 300-2500 nm, and data representing the results of this measurement are depicted in Fig.4-6 and Table 1 and 3. According to the spectral data, the maximum average total reflectances are found to be 94.9, 95.5, 95.0, 91.4 and 92.2 for bare Al reflector, dip, brush, spray and

25 flow coated Al reflector, respectively in the broad spectral range between

300 — 2500 nm. The maximum average specular reflectances are found to be 88.4, 90.0, 83.6, 89.5 and 87.7 for bare Al reflector, dip, brush, spray and flow coated Al reflector, respectively in the broad spectral range between 300 — 2500 nm

26

The average % transmittance over on glass cover plate are found to be 84.8, 84.6, 85.1, 84.8 and 84.9 (Table 3) for bare glass plate, dip, brush, spray and flow coated glass plate, respectively in the broad spectral range between 300 — 2500 nm. The water contact angles for the nonporous

s super hydrophobic (easy to clean property) single layer over on Al reflector plate were found be 54, 91, 100, 92 and 87 (Table 4) for bare Al reflector, dip, brush, spray and flow coated Al reflector, respectively. The water contact angles for the easy to clean single layer over on glass cover plate were found be 59, 107, 98, 100 and 105 (Table 5) for bare glass cover

10 plate, dip, brush, spray and flow coated glass cover plate, respectively

The super hydrophobic angle of water drops on the Al reflectors, glass cover plates and PV panels exhibits an easy to clean property. Fig. 10-11 depicted the super hydrophobic property of single layer coating on different substrates. The coating was also subjected to a bend profile test

is especially a super hydrophobic (easy to clean property) coating developed on Al reflector plates. For the above said test, 10 x 10 cm (lxw) coated Al plate was bended to reduce the length maximum up to 9x10 cm (lxw), after which the coating subsequently inspected by UV-Vis-NIR spectrometer for any losses of reflection due to bending process which

20 required for constructing the parabolic troughs. From the total reflectance measurement results (Table 6),. a very little change in the reflection property (<1 %) was noted after the bend profile test. Further, the coatings developed on Al reflector plates were subjected to a thermal cycle test at 2000C and the coating subsequently inspected for the presence of any

25 visual crack marks or losses of reflection property by SEM and UV-Vis-NIR spectrometer. From the SEM and UV-Vis-NIR spectrometer results (Table 7), no cracks and no remarkable changes in the coating morphology were observed and there is a remarkable increase of reflectance property (0.3 - 2.1%) for coated sample after the thermal cycle test. However the total

30 reflectance property of uncoated Al reflector sample was decreased about

27

1.2% after the test. The coating was also subjected to a salt pray test for proving the corrosion stability in a salt pray chamber following a ASTM method (ASTM 117 B) using with 5% NaCI solution and generating 15 psi vapor pressure using a chamber temperature of 290C. After every cycle

S test (25 hours) the coating subsequently inspected for the change of property of total reflectance by UV-Vis-NIR spectrophotometer. According to the invention (Table 8), Al reflector plate covering with a super hydrophobic (easy to clean) protective layer comprised by the composite metal oxides of fluorosilane modified composite metal oxide (ZrO2-5i02)

10 were found to have no remarkable changes in their reflectance even after lOOhrs salt spray test. The weather and UV stability of the coatings were studied in the environmental chamber using a ASTM standard test method (ASTM G155-98). According to the specified ASTM standard, the chamber environmental conditions of UV Irradiation intensity, water boiling point

15 temperature, air temperature, humidity, spray duration and UV irradiation duration are maintained precisely (1 cycle test comprises of 18 mm UV irradiation + 102 mm UV irradiation with spray of water (Intensity of UV light in the chamber; 0.35 W/m2, water boiling temp. 630C, humidity: 30%). From the test results, no changes in the reflectance properties, no

20 changes in the surface structure and no yellowing effect are observed after the test indicates that coatings are very stable against UV and weather. The performance results of PV panel (10 W power capacity) with a super hydrophobic (easy to clean property) coatings developed by spray, flow and brush coating techniques were tested at 250C by I-V

25 measurement equipped with an A.M 1.5G standard solar simulator (intensity 1000W / in2) and determined the efficiency of the PV panel, fill factor and a list of other solar cell parameters. Fig 11 and Table 10 depicted the efficiency, fill factor and other parameters of PV panels before and after coatings. According to the test results, no remarkable

30 changes in the panel efficiency and fill factor are observed after the coatings indicate that coatings are very transparent and free from pores,

28

voids and crakes which causing the efficiency loss of the PV panel due to loss of transmittance of light towards the absorber layer.

Example: 2

A super hydrophobic (easy to clean property) coating of SHC-2 system is S developed on Al reflectors and PV cover glass plates using another type of

coating sol. For this sol preparation, 9.19 g of Zirconium propoxide (70 %)

in n-propoanol Zr(n-Pro) was dispersed in 105.2g of isopropyl alcohol

(IPA), 17.34g of isopropoxy ethanol (IPE), 10.72 g 3-

Glycidoxypropyltrimethoxysilane (GPTS) and 2.66g 1H, 1H, 2H, 2H 10 perfluorooctylltriethoxysilane (PFOTS). Preparation procedure as well as

coating conditions for SHC-2 single layer coating were followed exactly same as example 1. The composition of the SHC-2 sol for the super hydrophobic (easy to clean property) single layer was Zirconium propoxide (70 %) in n-propoanol Zr(n-Pro): isopropyl alcohol (IPA),

15 isopropoxy ethanol (IPE): 3-Glycidoxypropyltrimethoxysilane (GPTS):

andlH, 1H, 2H, 2H perfluorooctylltriethoxysilane (PFOTS) = in the range of ratio 0 to 15 : 25 to 75: 5 to 25: 1 to 20: 0.5 to 5 (wt%) and preferably 6.33: 72.5:11.95: 7.38:1.85(wt%).

After the curing step, the single layer super hydrophobic (easy to clean 20 property) coating from this example was found to be non porous

morphological structure (no pores, voids and cracks). Moreover, the layer is clear, uniform and free of any visible defects. The refractive index and thickness of the coating layers developed by dip, flow, spray and brush coating processes were measured by ellipsometer and FE-SEM and found

25 to be 85nm, 300 nm, 1.5 pm and 1.5 pm, respectively. The refractive index of the layer was measured and found to be in the range 1.58 — 1.61 (at a wavelength of 546 nm). The coating's reflectance on the Al reflector and the coating transmittance on the glass plates were measured using a spectrophotometer over a broad solar wavelength range of 300-2500 nin,

29

and data representing the results of this measurement are depicted in Fig.7-9 and Table 2-3. According to the spectral data, the maximum average total reflectances are found to be 94.9, 95.0, 95.1, 93.10 and 92.4 for bare Al reflector, dip, brush, spray and flow coated Al reflector,

5 respectively in the broad spectral range between 300 — 2500 nm. The maximum average specular reflectances are found to be 88.4, 87.8, 88.4, 88.5 and 88.9 for bare Al reflector, dip, brush, spray and flow coated Al reflector, respectively in the broad spectral range between 300 — 2500 nm

The average % transmittance over on glass cover plate are found to be 10 84.8, 84.2, 80.4,78.9 and 80.4 for bare glass plate, dip, brush, spray and

flow coated glass plate, respectively in the broad spectral range between

300 — 2500 nm. The water contact angles for the nonporous easy to clean

single layer over on Al reflector plate were found be 54, 99, 93, 107 and

103 (Table 4) for bare Al reflector, dip, brush, spray and flow coated Al

1~ reflector, respectively. The water contact angles for the easy to clean single layer over on glass cover plate were found be 59, 106, 98, 101 and 89 (Table 5) for bare glass cover plate, dip, brush, spray and flow coated glass cover plate, respectively.

The coating was also subjected to various stability tests like bend profile, 20 salt spray, thermal cycle and UV-Weather stability similar to example 1.

From all the test results, no remarkable changes in the optical properties, no changes in the surface morphological structure (no crakes, no pores, no voids and no yellowing effect) are observed after the test indicates that coatings are very stable against thermal, corrosion, weather and UV

25 stabilities.

We have brought out the novel features of the invention by explaining some of the preferred embodiments under the invention, enabling a person in the art to understand and visualize our invention. It is also to be understood that the invention is not limited in its application to the details

30

set forth in the above description or illustrated in the drawings. Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, various modifications can be made without departing from the spirit and scope of the invention as described
s herein above and as defined in the following claims.

10

15

20

31

0 ~
We claim: 12

1. A super hydrophobic coating with high optical properties having easy to clean property, UV and corrosion resistance properties, adapted to apply on a substrate as single layer of composite sol comprising:

5 a) any one type or mixture of metal oxide precursors selected from

M(OR)4, MR1(OR)3, MR2(OR)2, MR3(OR), M(OR)3, MR2(OR), MR1(OR), MR3 and br MR4; where M is metal ion, selected from Zr, Si, Sn, Al, La, Nb and Ta; R is alkyl group, selected from methyl, ethyl, propyl, butyl and phenyl; OR is alkoxy group, selected from

10 methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, isopropoxyethoxy, methoxypropoxy, phenoxy, acetoxy, propionyloxy, ethanolamine, diethanolamin, triethanolamin, methacryloxypropyl, acrylat, methyacrylat and acetylaceton;

b) any one or mixture of alkylsilane compounds.selected from 15 3-glycidoxypropyltrimethoxysilane,

3-methacryloxypropyltrimethoxysilane,

3-acryl oxypropyltrimethoxysi lane,

2-methacryloxyethyltri methoxysi lane,

2-acryloxyethyltrimethoxysil ane,

20 3- methacryloxypropyltriethoxysilane,

3- acryloxypropyltriethoxysilane,

2- g lycidoxyethyltri methoxysi lane

3-glycidoxypropyltriethoxysilane and

2-glycidoxyethyltriethoxysilane;

25 c) any one or mixture of super hydrophobic agent, selected from perfluoroalkyl, perfluorocycloalkyl, polyethoxylated perfluoroalkyl and polyethoxylated perfluorocycloalkyl silane compounds;

32

2014

Q4 Qc~~L\1 4

d) any one or mixture of low 1or high boiling organic solvent

selected from methanol, ethanol, n-propanol, iso propanol, n butanol, isobutanol, n-pentanol, isopropoxy ethanol, diol and/or polyol.

5 2 A super hydrophobic coating as claimed in claim 1, wherein the constituents of the composite sol is having metal oxide precursor: low boiling point alcohol: high boiling alcohol: alkylsilane compound:

perfluoroalkylsilane or perflorocycloalkylsilane in the ratio of 0 to 15:

25to75:5to25: I to2O:0.5to5(wt%).

10 3. A super hydrophobic coating as claimed in claim 2, wherein the constituents of said composite sol is preferably having zirconium (IV) propoxide (Zr(iv)Pr): isopropanol (IPA): isopropoxy ethanol (IPETOH)

3-glycidoxy propyltrimethoxysilane (GPTS): IH, 1H, 2H, 2H- perfluorodecyltriethoxysilane(PFDTS) in the ratio of 6.3 : 72.4 :12

15 7.4:1.9(wt%).

4. A super hydrophobic coating as claimed in claim 2, wherein the constituents of said sol is preferably having, zirconium (IV) propoxide (Zr(iv)Pr): isopropanol (IPA): isopropoxy ethanol (IPETOH) : 3- glycidoxy propyltrimethoxysilane (GPTS) :1H, IH, 2H, 2H-

20 perfluorooctyltriethoxysilane(PFOTS) in the ratio of 6.3 : 72.5: 11.95:

7.4:1.85 (wt%)

5. A super hydrophobic coatings as claimed in claim 1, wherein said composite sol is prepared by:

a) mixing Zirconium propoxide thoroughly with a mixture of isopropyl 25 alcohol (IPA) and isopropoxy ethanol (IPE) and after which it is

allowed to age for 1-24hr ~ lS~ mixture);

33

¶ ~"i~

b) adding %~ O4O2~~Li4 3-Glycidoxypropyltrimethoxysilane (GPTS) slowly to said 1st

mixture, with stirring for l5min-lhr and after which it is allowed to age for 1-24hr (2nd mixture);

c) adding 1H, 1H, 2H, 2H perfluorodecyltriethoxysilane (PFDTS) or 5 perfluorooctylltriethoxysilane (PFOTS) slowly to the 2nd mixture,

with stirring for 15mm -lhr, (3rd mixture);

d) allowing to age the resultant 3rd mixture at room temperature for 1- 24hrs, preferably 24hrs with stirring condition enabling the solutions to undergo hydrolysis, polycondensation and polymerization at a

10 very slow rate.

6. A super hydrophobic coating as claimed in claim 1 to 5, is adapted to apply on different substrates selected among Al reflectors, glass substrates, PV panels, metal substrates, fabrics, leathers, Plastics, concretes, and ceramic tiles for harnessing solar energy.

15 7. A super hydrophobic coating as claimed in claim I to 5, is adapted to apply by a series of cost effective coating techniques selected from dip, spray, flow, brush, roll to roll coating techniques.

8. A super hydrophobic coating as claimed in claim I to 7,wherein said composite sol is applied on the said substrates comprising the step of

20 a) cleaning the substrate thoroughly with a mild detergent solution, rinsing with water followed preferably with deionised water, and then drying at about 50-1000C for 10-15 mm in an air—oven or hair drier for 2-5mm;

b) coating the cleaned substrate with said fluorosilane modified ZrO2-

25 SiO2 based composite sol;

c) drying the above coated substrate at about 50~100oC for 15-lhr in an air oven;

34

04.0 2~ ~ 4

I~1A

d) curing of the above coated substrate at about 100 - 20000 for 1 - 24hrs at a heating rate with 5-i000/ mm in the case of substrate selected from Al reflector or glass panel.

9. A super hydrophobic (easy to clean property) coating as claimed in S claim 8, wherein curing of the above coated substrate after step c) is

carried out at about 80 - 10000 for 1- 24hrs at a heating rate with 5- 1000/ mm, if the substrate is PV panels.

10. A super hydrophobic coating as claimed in claim I to 9 ,wherein coating is performed in a coating room having controlled humidity in

10 the range of 40-55% and temperature in the range of 20-25CC.

11. A super hydrophobic coating as claimed in claim ito 10, wherein the thickness of the layers is in the range between 85 nm to 1.5 pm, and preferably below 1.5 pm.

12. A super hydrophobic coating as claimed in claim 1 to 10, wherein the

15 refractive index of the layers is between 1.46 to 1.61 and preferably below 1.61.

13. A super hydrophobic coating as claimed in claim I to 10, wherein the water contact angle value of the layers on all the substrates is in the range between 87 to 1070.

20 14. A super hydrophobic coating as claimed in claim 1 to 10, wherein maximum average total reflectance and specular reflectance in the full solar range from 300-2500 nm for coatings on the Al reflector plate are in the range from 91.4 to 95.5% and 83.6 to 90.0%, respectively.

15. A super hydrophobic coating as claimed in claim I to 10, wherein

25 average transmittance in the range from 300~25O0 nm for coatings on the glass plate is in the range 80.4 to 85.1%.

35

~3 4

16. A super hydrophobic coating as claimed in claim 1 to 10, wherein it has a minimum loss of reflection < 1%, after bend profile test and exhibited high thermal, corrosion, weather and UV stability to withstand >lOOhr in salt spray, thermal cycle and UV & weather tests.

5 17. Articles coated with super hydrophobic coating as claimed in claim I to

16 such as optical devices, automobile widows, house hold appliances, metal sheets/tubes, fabrics, leathers, plastics, concretes and ceramic tiles.

10
Dated this j;day of 201
Director
15 International Advanced Research
Centre for Powder Metallurgy and
New Materials (ARCI)
~;R~L8uNOARARAJ*
L~CToR.ANr* /

36