Claims:We Claim:
1. Water borne heat resistant coating composition based on hybrid binder resin blend with <20% siloxane content comprising
a. 2-18 wt% Silicone Emulsion;
b. 2-23 wt% Acrylic polyol Emulsion having a hydroxyl value of 60 to 150 mg KOH/g and acid value 5 to 35 mg KOH/g;
c. 5-15 wt.% Aluminium Pigment;
d. 20-70 wt% water,
that is tolerant to upto at least 500°C exposure to heat.

2. Water borne heat resistant coating composition as claimed in claim 1 as a stable one pack coating composition wherein said hybrid binder resin blend with <20% siloxane content includes anticorrosive pigments and fillers in the range of 2-10 wt.% with said silicone emulsion at 60 wt.% solid content and said acrylic polyol emulsion at 45 wt.% solid content of respective resins being present in the ratio of 90:10 to 10:90.

3. Water borne heat resistant coating composition as claimed in claims 1 or 2 wherein said hybrid binder resin blend most preferably involves
a) 10 wt% Silicone Emulsion;
b) 11 wt% Acrylic polyol Emulsion having a hydroxyl value of 60 to 150 mg KOH/g and acid value 5 to 35 mg KOH/g,
with said silicone emulsion at 60 wt.% solid content and said acrylic polyol emulsion at 45 wt.% solid content present in the ratio of 56:46 in said blend is not only tolerant to heat but is also corrosion resistant.
4. Water borne heat resistant coating composition as claimed in claims 1-3 wherein said acrylic polyol emulsion having acrylic polyol resin at least at 45% solid content by weight and has hydroxyl value in the range of 60 to 150 mg KOH/g and acid value 5 to 35 mg KOH/g, is polymerization product of preferably 0 to 10 wt.% styrene, 5 to 40 wt.% MMA (Methyl methacrylate), 10 to 40 wt.% butyl acrylate, 14 to 35 wt% hydroxyethyl methacrylate and 0.7 to 5.5 wt% methacrylic acid on monomer solids, providing said hydroxyl and acid values.
5. Water borne heat resistant coating composition as claimed in claims 1-4 that is also corrosion resistant and is free of polysilazane, organosilicone phosphate, alkali metal silicate, inorganic silicic acid esters, titanate, Alumina sol, and specialty polymers including, PVDC, fluoro polymers to yet enable resistance to dry continuous heat upto 500 °C and intermittent heat resistance upto 550 °C.

6. Water borne heat resistant coating composition as claimed in claims 1-5 wherein said silicone emulsion comprises at least one emulsified silicone resin having at least one attached organic side group selected from the group consisting of phenyl, methyl and vinyl moieties.

7. Water borne heat resistant coating composition as claimed in claims 1-6 wherein said acrylic polyol emulsion having said acrylic polyol resin of hydroxy values in the range of 60 to 150 mg KOH/gm has number average molecular weight Mn of 1000 to 30000, more preferably 2000 to 20000, and Tg -60 °C to +60 °C more preferably -20 to 50 °C, and has an accelerated storage stability at 55 °C continuously over a period of 60 days with a less than 10% rise in viscosity.

8. Water borne heat resistant coating composition as claimed in claims 1-7 wherein said inorganic fillers are selected from the category of hydrated magnesium silicate, hydrated aluminium silicate, amorphous silica, phyllosilicate, barium sulphate, calcium carbonate, titanium dioxide.

9. Water borne heat resistant coating composition as claimed in claims 1-8 wherein said
anticorrosive pigments selected from zinc phosphate, zinc orthophosphate hydrate, organically modified basic zinc orthophosphate hydrate, strontium zinc phosphosilicate, zinc molybdenum phosphate hydrate, modified zinc calcium aluminium polyphosphate silicate and Zinc Calcium Strontium Phosphosilicate.

10. Water borne heat resistant coating composition as claimed in claims 1-9 wherein said coating composition comprises 2-5 wt.% of additives selected from rheological additives including Hydrophobically modified alkali swellable emulsions, Non-ionic associative thickeners based on hydrophobically modified polyether derivatives, hydrated magnesium aluminosilicate, Non-ionic associative thickeners based on hydrophobically modified polyurethane derivatives, organophilic phyllosilicates, nonionic synthetic associative thickeners and polyurea based liquid post-add rheological additive, surfactants like nonionic surfactant, dynamic wetting and molecular defoaming surfactants, tetramethyldecynediol, gemini surfactant, wetting and dispersing agent like VOC and solvent-free copolymer with pigment affinic groups.

11. A process for the preparation of water borne heat resistant coating composition as claimed in claim 1-10 comprising the steps of
I. providing hybrid binder resin blend with <20% siloxane content based on the following ingredients
a. 2-18 wt% Silicone Emulsion;
b. 2-23 wt% Acrylic polyol Emulsion having a hydroxyl value of 60 to 150 mg KOH/g and acid value 5 to 35 mg KOH/g;
c. 5-15 wt.% Aluminum Pigment;
d. 20-70 wt% water, and

II. blending said ingredients to obtain said water borne heat resistant coating composition that is tolerant to upto at least 500°C exposure to heat.

12. A process for the preparation of water borne heat resistant coating composition as claimed in claim 11 wherein said step (I) involves providing of acrylic polyol emulsion in the steps of
(i) Providing monomer mix of preferably 0 to 10 wt.% styrene, 5 to 40 wt.% MMA, 10 to 40 wt.% butyl acrylate, 14 to 35 wt% hydroxyethyl methacrylate and 0.7 to 5.5 wt% methacrylic acid;
(ii) Providing initiator mix including Tertiary butyl per benzoate;
(iii) Adding the monomer and initiator mix in select solvents of propylene glycol n-propyl ether for a period of 4 hours at 140-144 deg C followed by 1-hour digestion;
(iv) Adding tertiary butyl perbenzoate as chaser catalyst to the reaction mix of step (iii) in phases and polymerizing and continuing reaction for 1 hour followed by cooling to 70-80 deg ?C and terminating the reaction when desired molecular weight Mn of 2000 to 20000 is reached followed by adding water and amine neutralizer to disperse the acrylic polyol resin thus attained into water that is at least 45 % on solids and having hydroxyl value of 60 to 150 mg KOH/g and acid value 5 to 35 mg KOH/g prior to neutralization.

13. A process for the preparation of water borne heat resistant coating composition as claimed in claims 11 or 12 wherein said monomer mix includes acrylic monomers, vinyl monomers, carboxy functional monomers, together with initiators, water miscible solvents and neutralizing agents for preparing the acrylic polyols and includes the following
Said acrylic monomers including esters of acrylic and methacrylic acid such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, cyclohexyl, n-octyl, 2- ethylhexyl, lauryl, isobornyl or any combinations thereof, together with hydroxyl functional monomers including hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, their methacrylates or any combinations thereof may also be used. Hydroxyl or alkoxy functional derivatives of polyethylene glycol methacrylate or polypropylene glycol methacrylate or their acrylates including other -OH functional components containing unsaturation such as castor oil or castor oil fatty acid;
Said Vinyl monomers including styrene, alpha-methyl styrene, para-methyl styrene, or any combination thereof may be used to form the acrylic polyol.
Said Carboxyl functional monomers including acrylic acid, methacrylic acid, fumaric acid, crotonic acid, itaconic acid, maleic acid, cinnamic acid, 2-acrylamide-2-methylpropanesulfonic acid;
Said initiators including free radical polymerization thermal initiators including initiator may be azobisisobutyronitrile, tertiary-butyl perbenzoate, dimethyl 2,2'- azobis(2-methylpropionate), ditertiary butyl peroxide, dicumyl peroxide, ditertiary amylperoxide, or any combination thereof. Other initiator systems such as redox polymerization initiators may also be used such as benzoyl peroxide/amine systems.
Said neutralizing agent including primary, secondary or tertiary amine and their combinations. Examples of neutralizers include dimethyl ethanolamine, N-methylethanolamine, monoethanolamine, triethylamine, morpholine also including neutralizers such as liquor ammonia, sodium hydroxide or potassium hydroxide;
Said solvents including water miscible solvent selected from glycol ethers of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, ethylene glycol butyl ether, propylene glycol propyl ether and diethylene glycol monobutyl ether, esters, ethers and ketones or any combinations thereof

Dated this the 2nd day of August, 2021 Anjan Sen
Anjan Sen and Associates
(Applicants Agent)
IN/PA-199

, Description:FIELD OF INVENTION
The present invention provides for water borne heat resistant coating composition involving hybrid binder resin blend with < 20% siloxane content that is tolerant to upto 500°C exposure of heat, and is also preferably corrosion resistant.
BACKGROUND ART
The heat resistant coatings including water borne corrosion and heat resistant coatings have background hurdle that (1) Specialty polymers viz. Alumina sol, PVDC, fluoro polymers are used and also that (2) Primarily inorganic silicic acid esters such as TEOS, TMOS, Titanates such as Titanium Ethoxide and their sols are used as binders which require strong acid catalyst such as HCl etc. and that (3) Alkali metal silicates along with inorganic pigments such as Barium titanate are used.
On this reference is invited to the following prior arts
KR2184077B1 that discloses an acrylic polymer by emulsion polymerization of an acrylic monomer (A); and (b) the core emulsion of the first step and an acrylic monomer (A) and acrylic A shell containing a silicone-modified acrylic polyol polymer by emulsifying one or more monomers (B) selected from oxyalkoxysilane-based monomers and vinyl alkoxysilane-based monomers and a carboxylic acid monomer (C) containing a carboxyl group or a hydroxyl group. Relates to a method for producing a silicone-modified acrylic polyol polymer with a core-shell structure manufactured by the second process of forming an emulsion, and a high weather resistance eco-friendly aq. super heavy anticorrosive coating compounds including the same. The silicone-modified acrylic polyol polymer with a core-shell structure has excellent properties such as hardness and water resistance, and the paint compound containing it has excellent appearance such as gloss and clarity, and is highly weather-resistant and eco-friendly, esp. rust-resistant. It has excellent adhesion strength and is very suitable for use as an ultra-heavy coating material to prevent corrosion of steel materials in various steel structures including steel bridges, reinforced concrete, and power plants. This prior invention uses acrylic silicone co-polymer and not any physical blend of silicone emulsion and acrylic polyol emulsion.

JP 2012121323 teaches metal sheet has, on at least one side, color coating layer with thickness 2-10 µm containing (A) org. resin as a film-forming component, (B) color pigment, and (C) silica particles, wherein the metal sheet has surface roughness of Ra 0.7-1.5 µm (Ra = arithmetic av. surface roughness) and PPI 120-300 [PPI = peak no. per 1 in. (2.54 cm)]. The color coating layer may further contain (D) curing agent, (E) acrylic or silicone resin particles, and (F) polyethylene particles and be prepared by applying an aqueous paint compound and thermally drying. The metal sheet with chromate-free environmentally friendly coating layer has high corrosion resistance and scratch resistance. Thus, a percolated electro galvanized steel sheet was further coated with an aqueous composition containing adipic acid-2,2-dimethyl-1,3-propanediol-ethylene glycol-isophthalic acid-1,5-pentanediol-5-sodiosulfoisophthalic acid-terephthalic acid copolymer, polyether polyol (tetramethylene glycol/ethylene glycol)-2,2-bis(hydroxymethyl)propionic acid-hexamethylene diisocyanate-ethylenediamine copolymer triethylamine salt, an aqueous acrylic resin (Joncryl 61), carbon black (MA 100), colloidal silica (Snowtex N), spherical silica (HPS 1000), and polyethylene particle (Chemipearl W 950) and baked to give a coated steel sheet, showing the mentioned properties. This prior invention involves curing agent.

KR1221839B1 discloses surface treating compound is coated on a galvanized steel sheet with coating quantity of 500-1600 mg/m2 to form a thin film that has excellent gloss, heat-release property, corrosion resistance, blackening resistance and adhesive power even drying at 100-180°C. The compound comprises: (1) mixed resin containing main resin (at least one of water-dispersible polyolefin resin, Si-modified water-dispersible polyolefin resin, water-dispersible polyurethane resin, water-dispersible acrylic resin, water-soluble epoxy resin, water-soluble polyester resin and water-soluble amino resin) and melamine-based hardening agent that are mixed at a wt. ratio of 10:2-4 15-50 wt.%, (2) heat-release pigment (mean particle size = 2-10µm) containing at least two of graphite, carbon nanotube and graphene 8-15 wt.%, (3) inorganic metal sol (mean particle size = 5-30nm) containing at least one of silica sol, alumina sol, titania sol and zirconia sol 5-15 wt.%, (4) Organic metal complex containing at least one of silane-based coupling agent, titanium-based coupling agent and zirconium-based coupling agent 3-8 wt.%, (5) rust inhibitor 1-5 wt.%, and (6) water as balance. This prior invention contains inorganic metal salt and melamine based hardening agent.

KR20110076215 teaches two-component zinc type water base paint compound comprises a water-thinned liq. binder 100 wt. parts and zinc powder 230-250 wt. parts. Before the coating process, the water-thinned liquid binder and the zinc powder are mixed evenly, and then used. The two-component zinc type water base paint compound can prevent thermal oxidation of metals, i.e. iron, and has excellent corrosion resistance. The two-component zinc type water base paint compound is suitable for metal coating at high temp. of 500°C, so that it can be applied in metal refinery, food chem. plants, etc.
PURPOSE: A two-component zinc type aqueous paint composition is provided to ensure excellent properties of preventing thermal oxidation and corrosion resistance of metal materials such as iron materials, thereby enabling the coating of metal materials to which the heat of high temperature is applied. CONSTITUTION: A two-component zinc type aqueous paint composition separately comprises aqueous liquid binders and zinc powder. 100 parts by weight of aqueous liquid binders and 230~250 parts by weight of zinc powder are uniformly mixed before coating operation. The aqueous liquid binder includes, based on 100 parts by weight of purified water, 720~750 parts by weight of potassium silicate, 150~200 parts by weight of colloidal silica, 3~4 parts by weight of xanthan gum, and 2.5~3.0 parts by weight of octylphenolethoxylate. This prior patent refers to a two component water based zinc silicate coating which is using zinc powder as second component and first component is Potassium silicate and colloidal silica mixture, and does not refer to one pack coating using organically modified silicone emulsion but instead belongs to a class of a pure inorganic siloxane and silicates.
RU2355725 teaches a surface coating compound for units, machines and devices requiring corrosion protection and operating for long time at high-temp. (up to 500°) in flow of natural gas combustion products represented mainly by water and carbon dioxide such as in gas turbine units. The compound comprises 53.6-68.4 wt % of aluminum spherical particle powder filler and 46.4-31.6 wt % of a binder chosen from water glass with d. of 1.40-1.45 g/cm3 and modulus of 2.85-3.05 or its aq. soln. with d. of 1.12-1.18 g/cm3 and modulus of 2.85-3.05. The composition results in coating with strong adhesion and enhanced corrosion resistance under conditions of cyclic high-temp. up to 500°. This prior patent is involving aluminium spherical powder fillers 53.6 – 68.4 % by wt. and 46.4 -31.6 wt% binder chosen from water glass and does not involve any silicone emulsion 2 – 10% by wt. and Acrylic Poyol Emulsion 2 – 8% by wt.
RU 2304156 teaches aqueous composition for anticorrosive and heat-insulating covers over metal and concrete comprises silicon emulsion or silicon dispersion as a binding agent, mixt. of hollow microspheres different in size and bulk d. values and chosen from group comprising hollow glass microspheres, hollow ceramic microspheres, polymeric hollow microspheres and techno genic hollow microspheres, surface-active substance, titanium dioxide or zinc dioxide and, if necessary, other additives. The composition is used on pipe lines by being applied firstly as a thin layer on cold surface, followed by heating to 200-250°, repeating application of a thin layer on a hot surface, followed by application of metallic wire or net, or winding of pipe line with described cover by band layers with sep. bands made of steel (stainless) and where bands (small bands) are covered preliminary with above mentioned composition on one side and at least one of lateral band surfaces showing alternating projections and grooves of right-angled form and similar linear sizes. Grooves have flanges equal with grooves square and excluding dense adjoining of bands to pipeline surface during winding and also, creating an air layer. Joining of separate bands is carried out during winding and it is carried out using projections and grooves by connecting them as puzzle. This method provides pipes covers with high protective properties such as high heat-protection under effect of high temps. of 500-1000°, good anticorrosive properties and fire resistance. This prior patent is using hollow microspheres as heat insulating agent and thus relates to heat insulating coating and not any heat resistant coating. Also this prior patent does not require any organic binding agent and relate to any organically modified silicone emulsion and also organic Thermoplastic Acrylic Polyol Emulsion.
In view of the above state of the art disclosures and to overcome a hurdle in the art by avoiding (1) Specialty polymers viz. Alumina sol, PVDC, fluoro polymers, (2) Primarily inorganic silicic acid esters such as TEOS, TMOS, Titanates such as Titanium Ethoxide and their sols as binders which require strong acid catalyst such as HCl etc. and (3) Alkali metal silicates along with inorganic pigments such as Barium titanate in heat resistant coatings, there is a need in the art to explore for water borne corrosion resistant and heat resistant coating involving hybrid binder based coating composition containing < 20% siloxane content that would be heat resistant to upto 500°C exposure.

OBJECTS OF THE INVENTION
It is thus the primary object of the present invention to provide for heat resistant coating preferably water borne corrosion resistant and heat resistant binder based coating composition that would be heat resistant upto 500°C exposure to heat in containing <20% siloxane content.
Another object of the present invention is to provide for said heat resistant coating composition that would not require polysilazane, organosilicone phosphate, alkali metal silicate, inorganic silicic acid esters, titanate.
Yet another object of the present invention is to provide for said heat and corrosion resistance coating composition that would pass 1000 h at low DFT (@2 x 40 micron DFT) without use of any inorganic zinc silicate primer and withstand up to C4 environment
Another object of the present invention is to provide for said heat and corrosion resistance coating composition that would have good mechanical properties like abrasion resistance, pencil hardness and in having low siloxane content <20% without use of specialty polymers such as Alumina sol, PVDC, fluoro polymers and would also enable dry heat continuous resistance upto 500 °C and intermittent heat upto 550 °C.

SUMMARY OF THE INVENTION
Thus, according to the basic aspect of the present invention there is provided a water borne heat resistant coating composition based on hybrid binder resin blend with <20% siloxane content comprising
a. 2-18 wt% Silicone Emulsion;
b. 2-23 wt% Acrylic polyol Emulsion having a hydroxyl value of 60 to 150 mg KOH/g and acid value 5 to 35 mg KOH/g;
c. 5-15 wt.% Aluminium Pigment;
d. 20-70 wt% water,
that is tolerant to upto at least 500°C exposure to heat.

Advantageously said water borne heat resistant coating composition is a stable one pack coating composition wherein said hybrid binder resin blend with <20% siloxane content includes anticorrosive pigments and fillers in the range of 2-10 wt.% with said silicone emulsion at 60 wt.% solid content and said acrylic polyol emulsion at 45 wt.% solid content of respective resins being present in the ratio of 90:10 to 10:90.

Preferably in said water borne heat resistant coating composition said hybrid binder resin blend most preferably involves
a) 10 wt% Silicone Emulsion;
b) 11 wt% Acrylic polyol Emulsion having a hydroxyl value of 60 to 150 mg KOH/g and acid value 5 to 35 mg KOH/g,
with said silicone emulsion at 60 wt.% solid content and said acrylic polyol emulsion at 45 wt.% solid content present in the ratio of 56:46 in said blend is not only tolerant to heat but is also corrosion resistant.
Preferably said water borne heat resistant coating composition is provided wherein said acrylic polyol emulsion having acrylic polyol resin at least at 45% solid content by weight and has hydroxyl value in the range of 60 to 150 mg KOH/g and acid value 5 to 35 mg KOH/g, is polymerization product of preferably 0 to 10 wt.% styrene, 5 to 40 wt.% MMA (Methyl methacrylate), 10 to 40 wt.% butyl acrylate, 14 to 35 wt% hydroxyethyl methacrylate and 0.7 to 5.5 wt% methacrylic acid on monomer solids, providing said hydroxyl and acid values.
According to another preferred aspect of said water borne heat resistant coating composition the same is also corrosion resistant and is free of polysilazane, organosilicone phosphate, alkali metal silicate, inorganic silicic acid esters, titanate, Alumina sol, and specialty polymers including, PVDC, fluoro polymers to yet enable resistance to dry continuous heat upto 500 °C and intermittent heat resistance upto 550 °C.

Preferably in said water borne heat resistant coating composition said silicone emulsion comprises at least one emulsified silicone resin having at least one attached organic side group selected from the group consisting of phenyl, methyl and vinyl moieties.

More preferably in said water borne heat resistant coating composition said acrylic polyol emulsion having said acrylic polyol resin of hydroxy values in the range of 60 to 150 mg KOH/gm has number average molecular weight Mn of 1000 to 30000, more preferably 2000 to 20000, and Tg -60 °C to +60 °C more preferably -20 to 50 °C, and has an accelerated storage stability at 55 °C continuously over a period of 60 days with a less than 10% rise in viscosity.

According to another preferred aspect of the present invention in said water borne heat resistant coating composition said inorganic fillers are selected from the category of hydrated magnesium silicate, hydrated aluminium silicate, amorphous silica, phyllosilicate, barium sulphate, calcium carbonate, titanium dioxide.

Preferably said anticorrosive pigments selected from zinc phosphate, zinc orthophosphate hydrate, organically modified basic zinc orthophosphate hydrate, strontium zinc phosphosilicate, zinc molybdenum phosphate hydrate, modified zinc calcium aluminium polyphosphate silicate and Zinc Calcium Strontium Phosphosilicate.

More preferably said water borne heat resistant coating comprises 2-5 wt.% of additives selected from rheological additives including Hydrophobically modified alkali swellable emulsions, Non-ionic associative thickeners based on hydrophobically modified polyether derivatives, hydrated magnesium aluminosilicate, Non-ionic associative thickeners based on hydrophobically modified polyurethane derivatives, organophilic phyllosilicates, nonionic synthetic associative thickeners and polyurea based liquid post-add rheological additive, surfactants like nonionic surfactant, dynamic wetting and molecular defoaming surfactants, tetramethyldecynediol, gemini surfactant, wetting and dispersing agent like VOC and solvent-free copolymer with pigment affinic groups.

According to another aspect of the present invention is provided a process for the preparation of water borne heat resistant coating composition comprising the steps of
I. providing hybrid binder resin blend with <20% siloxane content based on the following ingredients
a. 2-18 wt% Silicone Emulsion;
b. 2-23 wt% Acrylic polyol Emulsion having a hydroxyl value of 60 to 150 mg KOH/g and acid value 5 to 35 mg KOH/g;
c. 5-15 wt.% Aluminum Pigment;
d. 20-70 wt% water, and

II. blending said ingredients to obtain said water borne heat resistant coating composition that is tolerant to upto at least 500°C exposure to heat.

In said process for the preparation of water borne heat resistant coating composition said step (I) involves providing of acrylic polyol emulsion in the steps of
(i) Providing monomer mix of preferably 0 to 10 wt.% styrene, 5 to 40 wt.% MMA, 10 to 40 wt.% butyl acrylate, 14 to 35 wt% hydroxyethyl methacrylate and 0.7 to 5.5 wt% methacrylic acid;
(ii) Providing initiator mix including Tertiary butyl per benzoate;
(iii) Adding the monomer and initiator mix in select solvents of propylene glycol n-propyl ether for a period of 4 hours at 140-144 deg C followed by 1-hour digestion;
(iv) Adding tertiary butyl perbenzoate as chaser catalyst to the reaction mix of step (iii) in phases and polymerizing and continuing reaction for 1 hour followed by cooling to 70-80 deg ?C and terminating the reaction when desired molecular weight Mn of 2000 to 20000 is reached followed by adding water and amine neutralizer to disperse the acrylic polyol resin thus attained into water that is at least 45 % on solids and having hydroxyl value of 60 to 150 mg KOH/g and acid value 5 to 35 mg KOH/g prior to neutralization.

According to another preferred aspect of the present process for the preparation of water borne heat resistant coating composition said monomer mix includes acrylic monomers, vinyl monomers, carboxy functional monomers, together with initiators, water miscible solvents and neutralizing agents for preparing the acrylic polyols and includes the following
Said acrylic monomers including esters of acrylic and methacrylic acid such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, cyclohexyl, n-octyl, 2- ethylhexyl, lauryl, isobornyl or any combinations thereof, together with hydroxyl functional monomers including hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, their methacrylates or any combinations thereof may also be used. Hydroxyl or alkoxy functional derivatives of polyethylene glycol methacrylate or polypropylene glycol methacrylate or their acrylates including other -OH functional components containing unsaturation such as castor oil or castor oil fatty acid;
Said Vinyl monomers including styrene, alpha-methyl styrene, para-methyl styrene, or any combination thereof may be used to form the acrylic polyol.
Said Carboxyl functional monomers including acrylic acid, methacrylic acid, fumaric acid, crotonic acid, itaconic acid, maleic acid, cinnamic acid, 2-acrylamide-2-methylpropanesulfonic acid;
Said initiators including free radical polymerization thermal initiators including initiator may be azobisisobutyronitrile, tertiary-butyl perbenzoate, dimethyl 2,2'- azobis(2-methylpropionate), ditertiary butyl peroxide, dicumyl peroxide, ditertiary amylperoxide, or any combination thereof. Other initiator systems such as redox polymerization initiators may also be used such as benzoyl peroxide/amine systems.
Said neutralizing agent including primary, secondary or tertiary amine and their combinations. Examples of neutralizers include dimethyl ethanolamine, N-methylethanolamine, monoethanolamine, triethylamine, morpholine also including neutralizers such as liquor ammonia, sodium hydroxide or potassium hydroxide;
Said solvents including water miscible solvent selected from glycol ethers of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, ethylene glycol butyl ether, propylene glycol propyl ether and diethylene glycol monobutyl ether, esters, ethers and ketones or any combinations thereof

DETAILED DESCRIPTION OF THE INVENTION
As discussed hereinbefore, the present invention provides for water borne heat resistant coating composition comprising based on hybrid binder resin blend with <20% siloxane content comprising in addition to pigments and fillers
a. 2-18 wt% Silicone Emulsion;
b. 2-23 wt% Acrylic polyol Emulsion having a hydroxyl value of 60 to 150 mg KOH/g and acid value 5 to 35 mg KOH/g;
c. 5-15 wt.% Aluminium Pigment;
d. 20-70 wt% water,
that is tolerant to upto at least 500°C exposure to heat.

Preferably said hybrid binder resin blend with <20% siloxane content having pigments and fillers comprises
a) 2-18 wt% Silicone Emulsion;
b) 2-23 wt% Acrylic polyol Emulsion having acrylic polyol resin with hydroxyl value in the range of 60 to 150 mg KOH/g and acid value 5 to 35 mg KOH/g;
c) 20-70 wt% water;
d) 5-15 wt.% Aluminium Pigment;
e) 2-10 wt.% Anticorrosive pigments;
f) 2-10 wt. % Inorganic fillers,
said silicone emulsion at 60 wt.% solid content and said acrylic polyol emulsion at 45 wt.% solid content of respective resins are non-reactive to reach other at room temperature and present in the ratio of 90:10 to 10:90, and said blend as a single pack coating composition is advantageously free of polysilazane, organosilicone phosphate, alkali metal silicate, inorganic silicic acid esters, titanate and is also free of specialty polymers such as Alumina sol, PVDC, fluoro polymers, and also does not require any curing/ hardener for forming films/getting cured.
Advantageously, said heat and corrosion resistance coating composition of the present invention passes 1000 h at low DFT (@2 x 40 micron DFT) without use of any inorganic zinc silicate primer and withstand up to C4 environment, possesses good mechanical properties (like abrasion Resistance, pencil hardness) and is heat resistance up to 500°C dry heat continuous and 550°C intermittent heat.
EXAMPLES:
Example 1: Synthesis of Acrylic Polyol Emulsion
The acrylic polyol is synthesized using free radical polymerization in propylene glycol n-propyl ether followed by amine neutralization process and dispersion of the resin in water. A 4 neck reactor with a condenser, stirrer, nitrogen inlet and metering pump is taken. The preferred formulation is given in Table 1.
Conventional acrylic monomers, initiators and water miscible solvents was employed to prepare the acrylic polyols.
Various esters of acrylic and methacrylic acid such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, cyclohexyl, n-octyl, 2- ethylhexyl, lauryl, isobornyl or any combinations thereof may be used to form the acrylic polyol.
Hydroxyl functional monomers such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, their methacrylates or any combinations thereof may also be used. Hydroxyl or alkoxy functional derivatives of polyethylene glycol methacrylate or polypropylene glycol methacrylate or their acrylates may also be used. Hydroxyl functional derivatives are preferred. Other OH functional components containing unsaturation such as castor oil or castor oil fatty acid may also be used.
Vinyl monomers such as styrene, alpha-methyl styrene, para-methyl styrene, or any combination thereof may be used to form the acrylic polyol.
Carboxyl functional monomers such as acrylic acid, methacrylic acid, fumaric acid, crotonic acid, itaconic acid, maleic acid, cinnamic acid, 2-acrylamide-2-methylpropanesulfonic acid may be used.
The acrylic polyol has a glass transition temperature (Tg) of -60 to +60 °C, more preferably -20 to 50 °C and a number average molecular weight of 1000 to 30000, more preferably 2000 to 20000. The acrylic polyol has a hydroxyl value of 60 to 150 mg KOH/g on solids, an acid value of 5 to 35 mg KOH/g on solids, and a solid content of 35 to 60% by weight of the aqueous polymer composition.
The polymerization may be carried out using free radical polymerization thermal initiators. The initiator may be azobisisobutyronitrile, tertiary-butyl perbenzoate, dimethyl 2,2'- azobis(2-methylpropionate), ditertiary butyl peroxide, dicumyl peroxide, ditertiary amylperoxide, or any combination thereof. Other initiator systems such as redox polymerization initiators may also be used such as benzoyl peroxide/amine systems.
The acrylic polyol may be neutralized using a neutralizing agent. The neutralizing agent can be a primary, secondary or tertiary amine and their combinations. Examples of neutralizers include dimethyl ethanolamine, N-methylethanolamine, monoethanolamine, triethylamine and morpholine. Other neutralizers such as liquor ammonia, sodium hydroxide or potassium hydroxide may also be used.
The acrylic polyol may be synthesized in a water miscible solvent such as glycol ethers of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol or any combinations thereof. Examples include ethylene glycol butyl ether, propylene glycol propyl ether and diethylene glycol monobutyl ether. Other solvents such as esters, ethers and ketones may also be used. The acrylic polyol, according to one or more embodiments of the disclosure, has an accelerated storage stability at 55 °C continuously over a period of 60 days with a less than 10% rise in viscosity.
Table 1: Formulation of the Acrylic polyol
1A 1B 1C
Sr. No. Monomer Composition Composition Composition
1 Styrene 5 5 0
2 MMA-Methyl methacrylate 21 13 18
3 Butyl acrylate 17 15 15
4 Hydroxyethyl methacrylate 0 10.5 10.5
5 Methacrylic acid 2.1 1.7 1.7
6 Tertiary butyl per benzoate 2 2 2
7 Tertiary butyl per benzoate (Added in phases as the reaction proceeds) 0.5 0.5 0.5
8 Propylene glycol n-propyl ether 10 10 10
9 N, N-dimethylaminoethanol 1.5 1.2 1.2
10 Water 40.9 41.1 41.1
Total 100 100 100

The above formulation can be also formulated free of styrene to give the desired properties under Table 3. (Composition 1C has been given in the table which is a styrene free acrylic resin). The monomer and initiator mix is added into propylene glycol n-propyl ether for a period of 4 hours at 140-144 deg C after which 1-hour digestion is allowed. After 1-hour digestion, chaser catalyst (tertiary butyl perbenzoate) addition is done and the batch is continued for 1 hour more. The batch is then cooled to 70-80 deg C and a mixture of water and amine neutralizer is added to disperse the resin into water. The resin parameters for resin 1A are as follows: %solids = 45%, hydroxyl value = 0 mg KOH/g, acid value = 30 mg KOH/g with a Tg of 25 ?C and resin parameters for resin 1B are as follows: % solids = 45%, hydroxyl value = 100 mg KOH/g, acid value = 25 mg KOH/g with a Tg of 25 ?C. Resin parameters for 1C are as follows: % solids = 45%, hydroxyl value = 100 mg KOH/g, acid value = 25 mg KOH/g with a Tg of 25 ?C.
The following as in Table 2 exemplify Water Borne Coating Composition for corrosion resistance and heat resistance to 500° C temperature in accordance and not in accordance with the present invention with Examples 2 & 13 being beyond the scope of the present invention.
Table 2
Ingredients Parts by weight (%)
Mill Base Examples 2 3 4 5 6 7 8 9 10
11
12
13
1 Aluminium Paste (water compatible) 17.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0
2 Wetting Agent (*Blocked copolymer with pigment affinic groups) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
3 Water 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0
4 Thickener (non-ionic synthetic associative thickener) 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50
5 Surfactant (Multifunctional) 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50
6 Hydrated Magnesium Silicate 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0
7 Modified Basic Zinc Orthophosphate Hydrate 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0
Emulsion Addition
8 Silicone Emulsion (60% solid content by weight, attached organic side group consisting of phenyl and methyl moieties) 19.08 17.17 15.27 13.35 11.45 10.0 9.54 7.63 5.72 3.82 1.92 0.0
9 Acrylic polyol Emulsion (Example 1B - having a hydroxyl value of 60 to 150 mg KOH/g, acid value 5 to 35 mg KOH/g and 45% solid content by weight) 0.00 2.55 5.09 7.62 10.18 11.0 12.72 15.27 17.8 20.35 22.89 25.44
Thinning Composition
10 Water 32.72 32.08 31.44 30.83 30.17 30.80 29.54 28.9 28.28 27.63 26.99 26.36
11 Rheology Modifier 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
Total 100 100 100 100 100 100 100 100 100 100 100 100

In Table 2, the ratio (% solid basis) of Silicone Emulsion (60% solid content by weight) and Non-Reactive Acrylic polyol emulsion (45% solid content by weight) decreases from Example 2 to Example 13 in an order of (2) 100:0, (3) 90:10, (4) 80:20, (5) 70:30, (6) 60:40, (7) 56.77:46.23, (8) 50:50, (9) 40:60, (10) 30:70, (11) 20:80, (12) 10:90 and (12) 0:100.

The above compositions of were prepared using High Speed Mixer (HSM) with variable RPM. Ingredients 1 to 3 were added in a cleaned stainless-steel container. Under slow speed stirring at RPM 200, for 10 minutes aluminium paste was soaked in water with the addition of wetting agent. Ingredient 4 to 7 were added sequentially in the container under slow speed stirring. Then RPM increased to 1400 RPM and continued for 30 minutes. Then finish checked on panel at an interval of 10 minutes to ensure lumps free dispersion. Then ingredients 8 & 9 (emulsions) added in the container and continued stirring at 700 RPM for 10 minutes. Then water and rheological additive added in the container and continued stirring at 700 RPM for 10 minutes.
Viscosity of all the examples (2 to 13) was found to be in the range of 75 – 190 gm on Stormer viscometer at 30 °C and solid content by weight (%): 32.5 ± 1.5 at 120°C for 1 hour.
For conducting mechanical tests like abrasion resistance, hardness, impact resistance etc. and long term performance tests, paint applied by conventional air spray gun on abrasive blast cleaned (to SA 2.5) carbon steel panels and for flexibility on manually cleaned tin panel. All mechanical tests performed after curing at 250°C for 1 hour and panels for long term test were subjected for testing after exposure to 500°C for 1 hour. Paint was applied in 2 coats and dry film thickness per coat maintained at 35 – 40 micron.
The coatings on the panels had the following properties as in Table 3.

Table 3
Examples
Property 2 3 4 5 6 7 8 9 10 11 12 13
Pencil Hardness
as per ASTM D 3363 Brittle film, failed with any pencil F F B HB F F B HB HB B B
Flexibility
as per ASTM D 522 ( ¼ inch) Failed Failed Failed Failed Failed Pass Failed Failed Failed Failed Failed Failed
Impact resistance (direct)
As per ASTM D 2794 7.1 J 7.1 J 7.1 J 7.1 J 7.1 J 7.1 J 7.1 J 7.1 J 7.1 J 7.1 J 7.1 J 7.1 J
Abrasion Resistance using CS10 wheel with 1000 gm load & following 500 cycles
as per ASTM D 4060 (weight loss) Metal exposed after 160 cycles 544 mg 490 mg 345 mg 290 mg 90 mg 124 mg 156 mg 200 mg 250 mg 256 mg 271 mg
Adhesion by tape test using Method B of ASTM D 3359 – 2 mm x 2 mm cross cut 0B 2B 3B 3B 4B 5B 4B 3B 3B 4B 4B 5B
Salt Spray Resistance for 1000 hrs as per ASTM B 117 Passed 196 hrs; after that over film rusting found Passed 250 hrs ; after that over film rusting found Passed after 400 hrs; after that over film rusting found Passed 500 hrs; after that over film rusting found Passed 700 hrs; after that over film rusting found Passed 1000 hrs without any defect and corrosion creepage upto 3 mm from scribed line Passed 800 hrs; after that over film rusting found Over film Rusting after 48 hrs Over film rusting 5after 200 hrs Over film rusting after 96 hrs Over rusting after 96 hrs Over film rusting after
96 hrs
Humidity Resistance as per ISO 6270 for 1000 hrs Passed 400 hours; after that over film rust found Passed 400 hours; after that over film rust found Passed 500 hours; after that over film rust found Passed 600 hours; after that over film rust found Passed 750 hours; after that over film rust found Passed 1000 hrs without any film defect Passed 800 hrs; after that over film rust found Passed 500 hrs; after that over film rust found Passed 96 hours; after that over film rust found Passed 96 hours; after that over film rust found Passed 72 hours; after that over film rust found Passed 48 hours; after that over film rust found
Heat resistance at 500°C for 25 cycles ( each cycle for 8 hours at 500°C and then immediate quenching in water at room temperature and then kept in dry condition for 16 hrs at 30°C) Cracking observed after 2 cycles Failed after 6 cycles
Failed after 6 cycles
Failed After 6 cycles Failed After 20 cycles Passed 25 cycles Failed After 15 cycles Failed After 10 cycles Failed After 5 cycles Failed After 5 cycles Failed After 2 cycles Failed After 1 cycle

Result & Discussion
In Table 2, the ratio (% solid basis) of Silicone Emulsion (60% solid content by weight) and Non-Reactive Acrylic polyol emulsion (45% solid content by weight) decreases from Example 2 to Example 13 in an order of (2) 100:0, (3) 90:10, (4) 80:20, (5) 70:30, (6) 60:40, (7) 56.77:46.23, (8) 50:50, (9) 40:60, (10) 30:70, (11) 20:80, (12) 10:90 and (12) 0:100.

From Table 3, it is obvious that as the Silicone Emulsion (60% solid content by weight) decreases and Non-Reactive Acrylic polyol emulsion (45% solid content by weight) increases from Example 2 to Example 13, the coating becomes more flexible and brittleness reduces. This is supported by the pencil hardness data and adhesion data. The values of both attributes again become inferior due to more thermo-plasticity development as acrylic polyol emulsion % increases. Due to decrease in brittleness, the weight loss during abrasion resistance test decreases from Example 2 to Example 7 and in case of Examples from 8 to 13 the values increase due to more thermoplastic nature and softness development.
Direct Impact resistance data is almost similar in all cases.
In case of salt spray resistance, humidity resistance and heat resistance, the trend of performance found to be superior from Examples 2 to 7 due to decrease in brittleness and increasing wetting property and the performance founds to be inferior due to increase in thermoplastic nature of the film.
From the above result, it can be inferred that Example 7 is the optimum design for attaining both heat tolerance and corrosion resistance properties.
Further Example 7 in Table 2, which is the most preferred design is prepared with Acrylic Polyol Emulsion, Example 1C as in Table 1, keeping all other ingredients same as in Example 7 in Table 2. It is tested against the set parameters and results obtained are in line with Example 7 as in Table 3.
Property Results
Pencil Hardness
as per ASTM D 3363 F
Flexibility
as per ASTM D 522 ( ¼ inch) Pass
Impact resistance (direct)
As per ASTM D 2794 7.1 J
Abrasion Resistance using CS10 wheel with 1000 gm load & following 500 cycles as per ASTM D 4060 (weight loss) 95 mg
Adhesion by tape test using Method B of ASTM D 3359 – 2 mm x 2 mm cross cut 5B
Salt Spray Resistance for 1000 hrs as per ASTM B 117 Passed 1000 hrs without any defect and corrosion creepage upto 3 mm from scribed line
Humidity Resistance as per ISO 6270 for 1000 hrs Passed 1000 hrs without any film defect
Heat resistance at 500°C for 25 cycles ( each cycle for 8 hours at 500°C and then immediate quenching in water at room temperature and then kept in dry condition for 16 hrs at 30°C) Passed 25 cycles

Further it is clearly shown under Table 1 and Table 2 thereunder, in Table 1 under 2 examples of binder (1A and 1B/1C), where the OH value is 0 mg KOH/g and the other where the OH value is 100 mg KOH/g. On storage stability of the paint (30 days at 55 ?C), there is phase separation of the paint where the OH value is 0 mg KOH/g and the paint is surprisingly stable where the OH value is 100 mg KOH/g. Further it is found that OH value range of 60 to 150 mg KOH/g and acid value 5 to 35 mg KOH/g works for the present invention when the paint remains stable. Thus, it is desirable to have an acrylic polymer with a hydroxyl functionality so as to ensure compatibility with the silicone emulsion and other ingredients so as to ensure a shelf stable composition.
Further to the above the present water borne heat resistant coating composition is simplistic with much less inventory management by avoiding polysilazane, organosilicone phosphate, alkali metal silicate, inorganic silicic acid esters, titanate, Alumina sol, that is also free of specialty polymers such as PVDC, fluoro polymers type ingredients, thus allowing a physical blend of acrylic polyol and silicone emulsion to be simply used without the additional step of carrying out an addition polymerization reaction using acrylic and vinyl/acrylic silane monomers or the additional step of high temperature condensation polymerization between an acrylic polyol and silanol or alkoxy functional siloxane intermediate, yet achieve exemplary heat tolerance at <20% siloxane content.
Further to the abovesaid the present invention is simplistic as it utilizes organically modified silicone emulsion and not a purely inorganic silicone component. The silicone content of the composition is less than 20 % vis-à-vis literature knowledge suggesting high siloxane contents in excess of 30% together with the complete absence of fluorinated component giving a cost benefit and hence a far better choice to the consumers in reaping heat tolerance benefits at economical rates.
Thus the major hurdle overcome by way of the present invention is the use of low content of siloxane <20% to attain the heat resistant effect at an economical price by involving a simple blend of acrylic and siloxane and not an acrylic siloxane copolymer, and without involving any hardener. It was found that when only organosiloxane emulsion is used the coating is having poor mechanical properties and shows cracking tendency at elevated temperatures, which issue of cracking and poor mechanical properties could be surprisingly overcome by physical blending of acrylic polyol emulsion having select hydroxyl and acid values enabling not only heat resistant and corrosion resistant properties but also adds to the stability of the water borne coating composition.
Additionally curing agents/ hardeners could be avoided by way of the present invention whereby the selection of the right ratio and Tg of the acrylic polyol with the organosilicone emulsion (said organosilicone emulsion formed by the emulsification of alkyl and or phenyl siloxane oligomers having alkoxy and or silanol functionality using surfactants and or colloidal stabilizers as per the known procedures reported in US5302658, US7875673) along with the fillers and pigments enables good film formation at room temperature without the use of hardener. While the silicone emulsion at room temperature is non-reactive, but at elevated temperatures, during heat ramp up to 500 ?C alkoxy/silanol functionality of the organosiloxane emulsion reacts with the -OH groups of the acrylic polyol. In addition, there will be a self-condensation reaction of the silicone emulsion enabling better film integrity of the coating composition remaining viable for multiple cycles.
The water borne heat resistant coating composition could be again advantageously provided as a one pack coating composition in involving an organosiloxane emulsion with an acrylic polyol without the use of any pure inorganic silicone/silicate component and crosslinker favouring a stable one component composition that is also further dependent on the hydroxyl value of the acrylic polyol resin-based emulsion as stated above.
Again where the conventional state of the art is known to use aluminium spherical powder fillers 53.6 – 68.4 % by wt. the present invention involves Aluminium pigment at much lower level of 5 – 15% by wt., with the aluminium spherical powder fillers and pigments are like asymmetrical flakes filler which could be advantageously dosed at much lower levels (5 to 15%) based on the specific level of involvement of acrylic polyol, silicone emulsion, pigments and fillers while ensuring an economical heat resistant coating composition.
It is thus possible for the present invention significantly finding that the selective –OH and acid values of the acrylic polyol resin based emulsion could ensure the storage stability of the water borne coating composition (30 days at 55 ?C) that is also heat resistant when physically blended with silicone emulsion as a one pack coating composition whereby there is phase separation of the coating composition, if the selective –OH and acid levels are not met. Thus, it is found to be workable only when an acrylic polymer with select hydroxyl functionalities were provided that ensured compatibility with the silicone emulsion and other ingredients thereby providing for a one pack shelf stable composition.