Description:FIELD OF THE INVENTION
The present invention relates to a coating composition useful to prevent the corrosion. Specifically, the present invention related to a novel two-layer coating system with self-healing functionality and improved adhesion along with super hydrophobicity. The said two-layer coating system includes a self-healing coating layer and a superhydrophobic coating layer.

BACKGROUND OF THE INVENTION
Corrosion becomes inevitable if the metal is exposed to moisture. Moreover, corrosion in marine environment is a huge problem as it led to the degradation of metallic materials due to an electrochemical reaction and hence, there is a requirement of corrosion protection.

The entropic inevitability of corrosion is currently being addressed by newer alloy designs, use of inhibitors and novel coating formulations with new additives. Traditional coatings could improve corrosion resistance. However, the protection offered by them will be compromised when the coating is mechanically damaged. Hence, it is a challenge to develop new coating system with self-healing functionality and improved adhesion. The most common method employed to overcome this damage is the incorporation of microencapsulated (MC) chemical agents such as polymerizable materials or corrosion inhibitors to the coatings to impart self-healing functionality.

Therefore, organic as well as inorganic Zn rich coatings are generally used as anticorrosion primers in various industries to impart corrosion protection in C5M and C5I corrosive areas. The idea is to employ the sacrificial protection offered by Zn particles in addition to the barrier protection offered by the primer. Upon damage to the coatings, the MC would release the encapsulated agent into the scratched area and coat the exposed area with a thin layer. When a scratch was made on the coatings, the large corrosion inhibiting molecules must compete with instantaneously reacting corrosive molecules such as oxygen, water, and chloride ions.

This is a challenge as the adsorption of organic molecules would take more time than that of simple oxygen reduction reaction. Further, inhibitors are less effective once corrosion has started and releasing of corrosion inhibitors is not sufficient for sustained self-healing property. Similarly, the use of larger concentrations of MCs are not advisable, since higher the concentration of MC, higher the stress formation and affects the integrity of the coating itself.

Few attempts have been made to add other chemical compounds to improve the corrosion protection at reduced amount of Zn particles in the coatings. Anticorrosive behaviour of a zinc-rich epoxy coating containing sulfonated polyaniline in 3.5% NaCl solution has been studied by Yang, Feng, et al. titled "Anticorrosive behavior of a zinc-rich epoxy coating containing sulfonated polyaniline in 3.5% NaCl solution." RSC advances, 2018, 13237-13247l. While Touzain et al. analysed the electrochemical and anticorrosion performances of zinc-rich and polyaniline powder coatings i.e., Meroufel, A., C. Deslouis, and S. Touzain titled "Electrochemical and anticorrosion performances of zinc-rich and polyaniline powder coatings" ElectrochimicaActa, 2008, 2331-2338.

Further, Ebrahimi et al. have evaluated the corrosion protection effects of emeraldine base Pani/clay nanocomposite as a barrier pigment in zinc-rich ethyl silicate primer along with comparative assessing on corrosion protection effects of zinc rich ethyl silicate primers modified with undoped and HCl doped PAni–clay nanocomposite. Akbarinezhad, E., M. Ebrahimi, F. Sharif, M. M. Attar, and H. R. Faridi titled "Synthesis and evaluating corrosion protection effects of emeraldine base PAni/clay nanocomposite as a barrier pigment in zinc-rich ethyl silicate primer" Progress in Organic Coatings, 2011, 39-44; Akbarinezhad, E., M. Ebrahimi, F. Sharif, and M. M. Attar. "Comparative assessing on corrosion protection effects of zinc rich ethyl silicate primers modified with undoped and HCl doped PAni–clay nanocomposite" Corrosion Engineering, Science and Technology, 2011, 777-781).

However, the previous work concludes that polymerizing self-healing agents added in form of micro capsules are not effective as they take time to form a polymeric layer over the damaged region and alternately corrosion inhibitor addition proves ineffective once corrosion initiates on steel. A need arises for development of an effective MC additive that can form a protective layer over metal such as steel with minimal addition of inhibitor.

On the other hand, super hydrophobic surfaces have attracted the interest of scientists and engineers for both fundamental research and their technological applications, such as contamination prevention, self-cleaning, anti-fouling surface designs, anti-icing, corrosion resistance of metals and their alloys, and biomedical and biological applications, among others. Nature has a way of designing biological structures to solve difficult engineering challenges. A few well-known examples are the various ways in which plants and animals adopt with either the abundance or paucity of water. For example, The Lotus leaf’s hierarchical roughness and surface chemistry bestow their exemplary and unique superhydrophobic properties; that is, water drops espouse a contact angle greater than 1500 and sway like marbles causing self-cleaning. On similar lines, during occasional fogs, water drops nucleate on water-philic pads on the backside of the Namib Sternocara Desert beetle. The water droplets grow and extend onto adjoining superhydrophobic regions allowing the beetle to incline its body and spin the water to its mouth for drinking. Although there are a wide range of commercially available hydrophobic coatings, there exist almost no superhydrophobic coatings (water contact angles greater than 1500). Most coatings of this type are classified as only being hydrophobic rather than superhydrophobic.

The distinction is made by water contact angles exceeding 1500 for superhydrophobic materials. Contact angles below this value render a material hydrophobic rather than superhydrophobic, and water tends not to roll as droplets. Moreover, a water contact angle of more than 1500 is achieved widely by the incorporation of fluorinated compounds in the coating formulation, it is widely known that the fluorinated compounds are expensive toxic and have limited uses in large scale industrial applications. On the other hand, due to their low surface energy silane-based compounds are also widely explored for the hydrophobic surfaces but lacks robustness and durability. The general practice is the use of three coat system for C5M environments.

Work has also been done on superhydrophobic coating composition based on fumed silica, nano silica, fluorosilane or orthosilicate along with polydimethylsiloxane and polyurethane or epoxy resin as mention in CN105419450B, US10493488B2 and JP05415962B2.

CN105949499A describes the general method for the preparation of superhydrophobic materials and their preparation by using nanotechnology and surface modification technology to modify various substrates like leather, cloth, and melamine foam.

US10131556B1 discloses hydrophobic nanoparticle compositions that include silica nanoparticles capped with asphaltene succinimide alkoxy silane compositions for crude oil collection. Similarly, superhydrophobic surfaces consisted of homogeneously mixed nanostructure and microstructure are disclosed in KR1410826B1.

KR1866501B1 discloses a superhydrophobic electromagnetic field shielding material having excellent electromagnetic field shielding performance and excellent durability while having superhydrophobicity. The curable resin is one thermosetting resin selected from the group consisting of epoxy resins.

Soft template and ultraviolet curing process to prepare surface super hydrophobic material where the oligomer used for superhydrophobic coating is one or more of epoxy methacrylate, epoxy acrylate, urethane acrylate and silicone urethane acrylate is disclosed in CN100412155C.

These coating have water contact angle greater than 1500 and used in mat, filter, vascular graft, textile, coating, and medical adhesive, outdoor, as icephobic coating composition or for drag reduction during turbulent flow.

However, toxic nature of superhydrophobic coatings developed using fluorinated compounds prevent their wide application. Silane based superhydrophobic compounds lack robustness and durability. Accordingly, an environmentally friendly and mechanically robust superhydrophobic layer with water contact angles greater than 1500 is necessary as replacement to current coatings.

Keeping in mind the drawbacks of the existing hydrophobic coating systems, a solution of superhydrophobic silicone-polyurethane (Si-PU) coating has been formulated, which upon ambient pressure and temperature drying develops, a nanoscopically rough silicon-PU on zinc silicate primer. The challenge is to preserve the desirable properties of the coatings to achieve effective self-healing with minimum loading of MCs. The present invention aims to replace the three-layer coating system with a two-layer coating system. The first coat is a self-healing zinc (Zn) coating layer, and the second coat is a superhydrophobic silicone-PU coating layer.

SUMMARY OF THE INVENTION
The present invention discloses a two-layer coating system which includes a zinc (Zn) coating layer and a silicone-polyurethane (Si-PU) coating layer. The zinc (Zn) coating layer includes a conducting polymer additive and a zinc (Zn) component, wherein the zinc (Zn) component is selected from an organic zinc (Zn) component, an inorganic zinc (Zn) component and/or a combination thereof.

The conducting polymer additive is polyaniline prepared by oxidative polymerization of aniline monomer. The conducting polymer additive is doped with an anion, wherein, the anion is a phosphate anion, a molybdate anion, a chloride anion and/or a combination thereof. Specifically, the anion is the phosphate anion. The zinc (Zn) component is inorganic zinc (Zn) component. The zinc (Zn) coating layer have a self-healing property. The silicone-polyurethane (Si-PU) coating layer is made up of silica, chloroform, polydimethylsiloxane, and isopropyl alcohol. The silicone-polyurethane (Si-PU) coating layer have a superhydrophobic property.

The process for synthesis of the zinc (Zn) coating layer includes steps of preparing a phosphate-doped polyaniline (PANI-PO4), then preparing a modified zinc dust by substituting a small amount of zinc dust with phosphate-doped polyaniline (PANI-PO4), and finally preparing the zinc (Zn) coating layer by adding a silicate binder slowly to the modified zinc dust by vigorous stirring. The silicate binder is an ethyl silicate binder. The ratio of the silicate binder to the modified zinc dust ranges from 3.1 to 1. The amount of the phosphate-doped polyaniline (PANI-PO4) ranges from 0.2-2 wt.%.

The process for synthesis of the silicone-polyurethane (Si-PU) coating layer comprises of preparing a first mixture by mixing fumed silica and chloroform; preparing a second mixture by mixing polydimethylsiloxane, chloroform, and isopropyl alcohol; and adding the first mixture to the second mixture and stirring for a period of 30-60 minutes to form a third mixture, adding a blend of polyol, hardener, and solvent to the third mixture to obtain the silicone-polyurethane (Si-PU) coating. The polyol is selected from Synpol AT-67, Synpol B-10, Terrol, Jeffol, DALTOLAC® not limited to and includes other kinds of polyether and polyester polyols. The hardener is selected from Desmodur N-75, Desmodur L-75, Konnate L-75, Borchi Gel L-75 N not limited to other isocyanate containing aliphatic and aromatic small and long chain molecules. The solvent is selected from xylene, butyl acetate or a combination thereof. The ratio of the polyol to the hardener ranges from 1:1.2.
OBJECTIVES OF THE PRESENT INVENTION
It is the primary objective of the present invention to develop a self-healing, superhydrophobic coating for corrosion protection for steel substrate.

It is one of the main objectives of the invention to enhance the corrosion protection by the addition of corrosion inhibiting pigment to Zn rich organic/inorganic coating system.

It is further objective of the present invention to synthesize conductive polymer effectively doped with suitable anions such as phosphates or molybdate or chloride for active corrosion protection which can ensures electrical connectivity between Zn particles and hence, do not jeopardize the galvanic corrosion protection offered by Zn particles.

It is also one of the main objectives of the invention to incorporate dopant anions in conducting polymer backbone that imparts self-healing ability to the coating against any corrosion attack.

It is further objective of the invention to enhance the superhydrophobicity and mechanical property to the second coating layer, achieved by using fumed silica as one of the constituent pigments and PDMS (a low surface energy polymer) as resin.

BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1: schematic representation of preparation of Si-PU coating layer on zinc silicate primer coated mild steel.

DETAILED DESCRIPTION OF THE INVENTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments in the specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated composition, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The composition, methods, and examples provided herein are illustrative only and not intended to be limiting.

The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.

Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods, and materials are now described. All publications mentioned herein are incorporated herein by reference.

The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and does not limit, restrict, or reduce the spirit and scope of the invention.

The abbreviations used are as following: PDMS (Polydimethylsiloxane); Si-PU (silicone-polyurethane); PAni (Polyaniline).

The present invention discloses that when a conducting polymer doped with suitable inhibitors were added to the coating formulation, the resultant coating could give superior coating protection to the existing Zn silicate primer. Further in the present invention, a solution of superhydrophobic silicone-polyurethane (Si-PU) coating has been formulated, which upon ambient pressure and temperature drying develops, a nanoscopically rough silicon-PU on zinc silicate primer. This combination of surface roughness and surface chemistry confer to the surface superhydrophobic properties.
Specifically, the invention discloses a zinc (Zn) coating layer formulated by addition of a conducting as well as corrosion inhibiting pigment, which when added to Zn rich organic/inorganic coating system, can enhance the corrosion protection. Further, the dopant anions incorporated in the conducting polymer backbone imparts self-healing ability to the zinc (Zn) coating layer against any corrosion attack. Further, a silicone-polyurethane (Si-PU) coating layer with sustained superhydrophobicity is coated over the zinc (Zn) coating layer. The superhydrophobicity and enhanced mechanical property of the second layer is achieved by using fumed silica as one of the constituent pigments and PDMS, a low surface energy polymer as resin.

In the present invention, the inorganic zinc silicate primer is modified by adding conducting polymer-based additives, which can be further doped with suitable corrosion inhibitors such as anodic, cathodic and a mixture thereof to get the best out of both the galvanic protection offered by Zn particles and active corrosion protection rendered by the corrosion inhibitor loaded conducting polymer additives. Further, the Si-PU top coating acts as a good barrier coating with excellent mechanical property and sustained superhydrophobicity.

According to an embodiment, the present invention discloses addition of a conducting as well as corrosion inhibiting pigment, which when added to Zn rich organic/inorganic coating system, can enhance the corrosion protection.

According to the main embodiment, the present invention discloses a two-layer coating system having a first coating layer and a second coating layer. The first coating layer is made up of a zinc (Zn) coating layer and the second coating layer is made up of a silicone-polyurethane (Si-PU) coating layer. The zinc (Zn) coating layer includes a conducting polymer additive and a zinc (Zn) component, wherein the zinc (Zn) component is selected from an organic zinc (Zn) component, an inorganic zinc (Zn) component and/or a combination thereof.

The conducting polymer additive is polyaniline prepared by oxidative polymerization of aniline monomer. The conducting polymer additive is doped with an anion, wherein, the anion is a phosphate anion, a molybdate anion, a chloride anion and/or a combination thereof. Specifically, the anion is the phosphate anion. The zinc (Zn) component is inorganic zinc (Zn) component. Wherein, the zinc (Zn) coating layer have a self-healing property.
The silicone-polyurethane (Si-PU) coating layer is made up of silica, chloroform, polydimethylsiloxane, and isopropyl alcohol. Wherein, the silicone-polyurethane (Si-PU) coating layer have a superhydrophobic property.

In another embodiment, superhydrophobicity and enhanced mechanical property to the second coating layer is achieved by using fumed silica as one of the constituent pigments and PDMS, a low surface energy polymer as resin.

In an embodiment, the present invention discloses a process for synthesis of the zinc (Zn) coating layer which includes steps of preparing a phosphate-doped polyaniline (PANI-PO4), then preparing a modified zinc dust by substituting a small amount of zinc dust with phosphate-doped polyaniline (PANI-PO4), and finally preparing the zinc (Zn) coating layer by adding a silicate binder slowly to the modified zinc dust by vigorous stirring. The silicate binder is an ethyl silicate binder. The ratio of the silicate binder to the modified zinc dust ranges from 3.1 to 1. The amount of the phosphate-doped polyaniline (PANI-PO4) ranges from 0.2-2 wt.%.

In an embodiment, the present invention discloses a process for synthesis of the silicone-polyurethane (Si-PU) coating layer comprises of preparing a first mixture by mixing fumed silica and chloroform; preparing a second mixture by mixing polydimethylsiloxane, chloroform, and isopropyl alcohol; and adding the first mixture to the second mixture and stirring for a period of 30-60 minutes to form a third mixture, adding a blend of polyol, hardener, and solvent to the third mixture to obtain the silicone-polyurethane (Si-PU) coating. The polyol is selected from Synpol AT-67, Synpol B-10, Terrol, Jeffol, DALTOLAC® not limited to and includes other kinds of polyether and polyester polyols such as Polytetramethylene ether glycol, Polyethylene glycol, Poly propylene glycol, Sorbitol, Sucrose, Acclaim®, Arcol®, Baygal®, Desmophen®, Hyperlite®, Multranol®. The hardener is selected from Desmodur N-75, Desmodur L-75, Konnate L-75, Borchi Gel L-75 N not limited to other isocyanate containing aliphatic and aromatic small and long chain molecules such as Methyl phenylene diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate, naphthalene diisocyanate, methylene bis-cyclohexylisocyanate (HMDI), isophorone diisocyanate. The solvent is selected from xylene, butyl acetate or a combination thereof. The ratio of the polyol to the hardener ranges from 1:1.2.
In another embodiment, the two-layer coating system is applied over mild steel plates and its corrosion protection performance is evaluated. The conducting pigments ensures the electrical connectivity between the Zn particles and hence, do not jeopardize the galvanic corrosion protection offered by Zn particles. Further, the dopant anions incorporated in the conducting polymer backbone imparts self-healing ability to the coating against any corrosion attack. Finally, silicone-polyurethane (Si-PU) coating layer with sustained superhydrophobicity is coated over the zinc (Zn) coating layer. Wherein, the zinc (Zn) coating layer is a self-healing inorganic Zn silicate coating layer. The silicone-polyurethane (Si-PU) coating layer have contact angle between 135-1550.

Wherein, the elemental composition of the silicone-polyurethane (Si-PU) coating layer have 71.3%, 22.6%, 2.94% and 3% of C, O, N and Si respectively.

Further, morphologically the coating is found to be particulate. The coating was found to be intact even after the 50 rubs with Ethyl methyl ketone (solvent rub test ASTM D5402). The coated panels were tested in a taber abraser (loaded with 1 Kg) for 100 cycles. Wear index calculated as per ASTM D4060. The Taber wear index indicates rate of wear is calculated by measuring the loss in weight (in milligrams) per 100 cycles of abrasion. The lower the wear index, the better is the abrasion resistance. No appreciable weight loss and the contact angle remained the same before and after abrasion test.

In another embodiment, the invention provides that, the pull-off adhesion test conducted for the silicone-polyurethane (Si-PU) coating layer also referred to as the hydrophobic coating and which is applied on self-healing inorganic Zn silicate coating. The pull-off adhesion test showed high adhesive fracture of coating, as per the ASTM D4 with an average pull off adhesion strength of 1.73 MPa. The aluminium dollies were fixed on the painted panels using araldite and allowed to cure for 7 days.

In another embodiment, the invention provides, that the coating is found to be stable between 30 – 360 ?.

In another embodiment the invention provides that, no rust formation is found in salt spray test even after 5000 h of exposure in 3.5% NaCl solution.

Synthesis of conducting polyaniline:
The synthesis of the zinc (Zn) coating layer initially includes synthesis of phosphate doped conducting polyaniline. Wherein, preparation of the phosphate doped conducting polyaniline.is completed by dissolving 1M distilled aniline in 500 ml of 1M solution of phosphoric acid. Then adding drop-wise, pre-cooled 1M solution of ammonium per sulphate (APS) to the pre-cooled aniline-acid mixture for about 1.5 h with constant stirring. The reaction is conducted at 5 ± 2 °C, finally, separating the dark green coloured phosphate doped conducting polyaniline (PANI).

Synthesis of the zinc (Zn) coating layer:
In another embodiment, the invention provides the method for the preparation of a zinc (Zn) coating formulation, wherein, zinc dust is slowly added to ethyl silicate binder with vigorous stirring in the ratio of 1:3.1 by volume respectively.

In another embodiment, the invention provides that the zinc (Zn) coating layer is prepared by substituting small amount of zinc dust with conducting polyaniline.

In another embodiment, the invention provides that the unmodified zinc silicate primer and PAni-PO4(having 0.2, 0.5, 1, 2 wt. %) modified zinc silicate primers are tested for their corrosion resistance properties according to ASTM B-117 method. The cross scribes made down to the metal surface in order to observe the protective action of the primers.

In an embodiment, the invention provides various coating formulation with various amount of self-healing conducting polymer pigment which is given in the below table 1. The mixing ratio of part A to part B is 3.1 volume(s) Part A to 1 volume(s) Part B. A typical coating formulation for 100 ml paint is given here.
Table 1

Sr. No.
Name of the coating
Mixing components
Formulation of coating (100ml)
1. Zinc rich ethyl silicate without PANI-PO4 Ethyl silicate and Zinc dust Part A=75.61ml
Part B=173.9g
PANI-PO4 = NIL
2. Zinc rich ethyl silicate+ 0.2 wt.% PANI-PO4 Ethyl silicate, Zinc dust andPANI-PO4 Part A=75.61ml
Part B=173.552 g
PANI-PO4 = 0.348 g
3. Zinc rich ethyl silicate+ 0.5 wt.% PANI-PO4 Ethyl silicate, Zinc dust and PANI-PO4 Part A=75.61ml
Part B=173.031 g
PANI-PO4 = 0.869 g
4. Zinc rich ethyl silicate+ 1.0 wt.% PANI-PO4 Ethyl silicate, Zinc dust and PANI-PO4 Part A=75.61ml
Part B=172.161 g
PANI-PO4 = 1.739 g
5. Zinc rich ethyl silicate+ 2.0 wt.% PANI-PO4 Ethyl silicate, Zinc dust and PANI-PO4 Part A=75.61ml
Part B=170.422g
PANI-PO4 = 3.478 g
Wherein, Part A is Ethyl silicate, Part B is Zinc dust and PANI-PO4
Synthesis of silicone-polyurethane (Si-PU) coating:
In another embodiment, the invention provides the preparation of superhydrophobic coating wherein, two different mixtures were initially prepared i.e., a first mixture and a second mixture. The first mixture contained fumed silica and chloroform while the second mixture included Polydimethylsiloxane, chloroform & Isopropyl alcohol. The polydimethylsiloxane was mixed in a different container in order to be hydrolysed. First mixture with different concentrations of fumed silica and 16.5g chloroform was mixed using a magnetic stirrer for 2 hours. Also, second mixture with 0.5 g Polydimethylsiloxane, 10 g chloroform & 10g IPA was mixed in a magnetic stirrer for 45 min. Then, first mixture was added to second mixture and stirred for 30-60 minutes to form a third mixture. Finally, a blend of polyol, hardener (the ratio of polyol to hardener was adjusted to be (1:1.2) and solvent (xylene and butyl acetate) was added to the third mixture and the final coating was applied on the steel substrate (3 x 2 inch) by a spray gun. Equal ratio of the solvent is added to the polyol and hardener. The thickness of coating was found to be 110 ± 5 µm (an average of three points were reported). The schematic representation of preparation of Si-PU coating on zinc silicate primer coated mild steel is shown in Figure 1 wherein,
01: Vial – A containing Fumed silica and CHCl3 stirred for 2 hr;
02: Vial – B containing PDMS, CHCl3and IPA stirred of 45 min;
03: Vial – C containing blend of polyol and hardener in the ratio of 1:1.2 and solvent (xylene and butyl acetate);
04: Stirred for 40 min;
05: Stirred for 25 min;
06: Si-PU coating on Zinc silicate primer coated mild steel;
07: length of coated substrate is 3 inches; and
08: width of coated substrate is 2 inches.

In an embodiment, the comparison of the disclosed two-layer coating system with commercially available Silicone-PU have been performed.

Table 2: comparison of the present invention to commercial Silicone-PU coating
Properties Commercial Silicone-PU (Nanomyte® Coatings) Achieved Targets
Contact angle 100-1200 135-1550
Pull-off adhesion strength 1.0 MPa 1.82 MPa
Pencil Hardness 2H - 5H 6H
Taber abrasion test ?Haze (1 Kg load, 100 rotations) ?Haze (1 Kg load, 100 rotations) (wear index – 0.05)
Thermal Stability -25 oC to 176 oC 30oC to 300oC , Claims:1. A two-layer coating system comprising:
a first coating layer, wherein the first coating layer comprises a zinc (Zn) coating layer; and
a second coating layer, wherein the second coating layer comprises a silicone-polyurethane (Si-PU) coating layer.

2. The coating system as claimed in claim 1, wherein the zinc (Zn) coating layer comprises a conducting polymer additive and a zinc (Zn) component, wherein the zinc (Zn) component is selected from an organic zinc (Zn) component, an inorganic zinc (Zn) component, and a combination thereof.

3. The coating system as claimed in claim 1, wherein the conducting polymer additive is polyaniline prepared by oxidative polymerization of aniline monomer.

4. The coating system as claimed in claim 1, wherein the conducting polymer additive is doped with an anion, wherein, the anion is a phosphate anion, a molybdate anion, a chloride anion, and a combination thereof.

5. The coating system as claimed in claim 1, wherein the anion is the phosphate anion.

6. The coating system as claimed in claim 1, wherein the zinc (Zn) component is inorganic zinc (Zn) component.

7. The coating system as claimed in claim 1-6, wherein the zinc (Zn) coating layer have a self-healing property.

8. The coating system as claimed in claim 1, wherein the silicone-polyurethane (Si-PU) coating layer comprises silica, chloroform, polydimethylsiloxane, and isopropyl alcohol.

9. The coating system as claimed in claim 1, wherein the silicone-polyurethane (Si-PU) coating layer have a superhydrophobic property.

10. A process for synthesis of the zinc (Zn) coating layer as claimed in claim 1, the process comprising:
preparing a phosphate-doped polyaniline (PANI-PO4);
preparing a modified zinc dust by substituting a small amount of zinc dust with phosphate-doped polyaniline (PANI-PO4); and
preparing the zinc (Zn) coating layer by adding a silicate binder slowly to themodified zinc dust by vigorous stirring.

11. The process as claimed in claim 10, wherein, the silicate binder is an ethyl silicate binder.

12. The process as claimed in claim 10-11, wherein a ratio of the silicate binder to the modified zinc dust ranges from 3.1 to 1.

13. The process as claimed in claim 10, wherein amount of the phosphate-doped polyaniline (PAni-PO4) ranges from 0.2-2 wt.%.

14. A process for synthesis of the silicone-polyurethane (Si-PU) coating layer as claimed in claim 1, the process comprising:
preparing a first mixture by mixing fumed silica and chloroform;
preparing a second mixture by mixing polydimethylsiloxane, chloroform, and isopropyl alcohol; and
adding the first mixture to the second mixture and stirring for a period of 30-60minutes to form a third mixture,
adding a blend of polyol, hardener, and solvent to the third mixture to obtain the silicone-polyurethane (Si-PU) coating.

15. The process as claimed in claim 14, wherein the polyol is selected from Synpol AT-67, Synpol B-10, Terrol, Jeffol, DALTOLAC®, polyols of polyether, and polyols of polyester.

16. The process as claimed in claim 14, wherein the hardener is selected from Desmodur N-75, Desmodur L-75, Konnate L-75, Borchi Gel L-75 N, isocyanate containing aliphatic and aromatic small and long chain molecules.

17. The process as claimed in claim 14, wherein the solvent is selected from xylene, butyl acetate, and a combination thereof.

18. The process claimed in claim 14, wherein a ratio of the polyol to the hardener ranges from 1:1.2, and wherein equal ratio of the solvent is added to the polyol and hardener.