TITLE:
A water borne polyurethane based coating for Galvanized steel
FIELD OF THE INVENTION:
The present invention is related to a waterborne coating More specifically, the invention is related to interpenetrating linkage between polyurethane based dispersion and amino functional poly-siloxane The polyurethane based coating enhance the impermeability of ions and water rolling off effect on Galvanized (GI) iron.
BACKGROUND OF THE INVENTION:
Polyurethane dispersions are known in the art however, the known polyurethane dispersion does not exhibit the good crosslinking which results the failure in adhesion This results in poor corrosion resistance properties Researchers have attempted in past crosslinking polyurethane dispersion with isocyanate compounds This scheme improves the crosslinking however, the resultant polymer matrix becomes very brittle and hard on curing at high temperature This high temperature is required to emit the blocking agent which increases the risk of hazardous and volatile components
A number of attempts have been made to develop polyurethane based coating US6395265B1 describes, A polysiloxane -polyurethane based coating (multiblock ionizable polycondensates) which is used for cosmetic or dermatological compositions with film-forming properties Also, it is usable for treatment of keratin substances like skin, hair and nails, Make-up products like nail varnish, mascaras, eyeliners etc., to use a variable proportion
US5760123 A reveals to a waterborne polyurethane dispersion for production of multilayer lacquer coatings, They are suitable as an industrial application for binders in aqueous base This dispersion contains polyurethane resin having 2500 to 1000000 molecular weight with 2 to 150mmol siloxane moieties per 100 g of solid resin It has no hydroxysilyl and alkanoyloxysilyl groups for crosslinking

US3941733A describes, A dispersion of poly (urethane-urea which terminated by silyl groups and forms self-assisting films and coating on webs It also contains carboxyl groups It is usable on woven and non-woven webs, leather for improved wear resistance, glass fibers, wood, aluminum etc These polymers are isocyanate terminated polymers so that the material can be bonded to the leather
WO1995028429A1 reveals, an aqueous dispersion of siloxane containing polyurethane which is being used for the production of multilayer coatings, aqueous coatings and foundation varnish for multiple-coat varnishes. The polyurethane resin's molecular weight is about 2500-1000000, containing 2-150mmol of -Si-O-Si per 100 gm of solvent free polyurethane resin, This aqueous dispersion contains a hydrophilic group (ethanol)
US6632915B1 describes, a polyurethane which contains hydrophilic functional group i e, ethenylarylene This product is produced by polyurethane prepolymer (having at least one free isocyanate group) reacting with ethenylarylene monoisocyanate with a polyol, polyamine and compound having hydroxyl and amino groups in 1:1 molar ratio It is being used to prepare coating materials, adhesives, and sealing compounds,
US6046295A reveals a polyurethane based graft copolymer to produce coating materials, adhesives, sealing materials, single coat or multicoated decorative and protective paint, The polyurethane terminated by hydrolyzed silyl groups which contains carboxyl groups It provides high gloss, solvent resistance, tough, scratch resistance and light stability These coating are particularly useful for coating for wood floorings, furniture and marine surfaces.
US5760155A describes a polysiloxane polyurethane composition which is formed by mixing polyisocyanate, a polyol, a hydroxyl-carbinol containing silicon material It is used in various types of fillers, pigments, solvents, and additives for enhancing pigment wetting and flow control. This combination enhances the abrasion, impact, chemical and weather resistance with tensile strength, tear strength and elongation. It is being used in the applications in the textile, paper, automotive, sports and recreation, wood, civil engineering and construction, marine and industrial maintenance coatings markets.

WO 1999021904A1 reveals, two and three component polyurethane compositions, providing chemical resistance without reduction in abrasion resistance and flexibility. The composition comprises hydroxyl functional aliphatic polyurethane dispersion in water combined with an aromatic polyether and cross-linked with an aliphatic/aromatic polyisocyanate. It is usable in the production of coatings and providing excellent hardness, flexibility, solvent resistance and surface appearance.
In light of the above prior art, there is still need of synthesizing a coating that can provide high corrosion resistance and is easily curable. The coating needs to possess gloss, good water rolling effect and excellent adhesion with metallic substrate.
OBJECTS OF THE INVENTIONS:
It is therefore, an object of the present invention to propose the synthesis of cycloaliphatic polyurethane dispersions which is further be modified by inserting polydimethylsiloxane and ami no-functional poly-siloxane solutions in different concentrations
Another objection of the present invention is to provide a coating that provides corrosion resistance and improved rolling effect with reduced surface tension on GI substrate,
Still another object of the invention is to develop a water borne coating that has excellent adhesion with metallic substrate.

Summary of the Invention:
The invention claims a polyurethane based dispersion grafted with 4 to 10 weight % of aminopropyl trimethyl polysiloxane. Aminopropyl trimethyl polysiloxane is synthesized with a novel approach using aminopropyl ethoxy dimethoxy silane and methyl butoxyethoxymethoxy silane. The grafed polyurethane based formulation provides excellent adhesion, excellent gloss retention with a high gloss, good water rolling effect and high corrosion resistance.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig 1 shows synthesis of grafted polyurethane dispersion (G-PUD) Fig 2 shows tafel analysis for example 2 to 5 with example 1 Fig 3 shows tafel analysis for Example 6 to 8 with example 1
DETAILED DESCRIPTlOIN OF THE INVENTION:
The water borne polyurethane based coating composition is prepared by combining a polyurethane dispersion with 4 to 10 wt % of aminopropyl trimethyl polysiloxane The present invention describes a synthesis of polyurethane dispersion (PUD) modified by a aminopropyl trimethyl polysiloxane Aminopropyl trimethyl polysiloxane is result of the hydrolysis and condensation of aminopropyl ethoxy dimethoxy silane and aminopropyl butoxyethoxymethoxy silane exhibiting excellent impermeability of corrosive ions and improved water rolling effect with reduced surface tension of coating solution on steel surfaces especially on zero spangled GI The
The reaction scheme as per the current invention is depicted below and explained with accompanying description below.

polyurethane dispersion (PUD) [Yj is synthesized by taking the mixture of 64 wt % of polyurethane resin (15000-16000gm molecular weight) and 2 mg KOH/g acid value, 32 wt, % of demineralized water into a reaction vessel for an hour at 60°C with a continuous passing the argon gas and then keep the vessel for cooling Then, further 1 wt % of ethyl tri-ethoxy silane (192 33 molecular weight), 0 5 wt % of silicon based flow additive and 2 5 wt % of zinc phosphate based rust inhibitor were mixed into above prepared solution with a continuous stirring for 15 minutes In an embodiment of the invention, silicon based flow additive is a solution of a polyether siloxane copolymer. In an embodiment of the invention, the rust inhibitor is zinc phosphate based rust inhibitor having the formula CaH08PSiSrZn,
The polyurethane dispersion as per the current invention is a cycloaliphatic thermoplastic based polyurethane dispersion with molecular weight in the range of 15000 to 16000 The polyurethane dispersion is having at least one functional group of -N-H- with -0-C=0 and represented by formula:[-OOCNH-R1-NHCOO-R2-], where R1 is C5 to C40 containing cyclohexyl/tricyclononane structure and R2 is C6 to C40 containing cyclopentyl/ethylene biscyclopentyl structure.
Synthesis of aminopropyl trimethyl polysiloxane: In a reaction vessel, 5 wt % (0 028 moles) of aminopropyl ethoxy dimethoxy silane, repsented by formula [A] in the reaction scheme and 5 wt. % (0L026 moles) of methyl butoxyethoxymethoxy silane [B]) are mixed with a high speed stirring in 1:1 ratio in presence of 0 001 wt,% (5 00001 moles) of acetic acid in 90 wt, % of demineralized water.
Aminopropyl ethoxy dimethoxy silane [A] and methyl butoxyethoxymethoxy silane [B] are converted into 001265 moles of aminopropyltrisilanol [C] and 0 0272 moles of methyltrisilanol [D] respectively along with 5 moles of acetified water and form a product "aminopropyl trimethyl polysiloxane", represented by formula [X] Remaining part is 0 01415 moles (Q) of residue This residue contains methanol, ethanol and butanol.
Synthesis of polyurethane dispersion (PUD) modified by aminopropyl trimethyl polysiloxane
4 to 10 wt % of aminopropyl trimethyl polysiloxane is poured gradually with slow stirring up to 15 minutes into a vessel containing polyurethane dispersion [Y] This results in polyurethane

dispersion grafted aminopropyltrimethylpolysiloxane as depicted in the formula [Z]. The Aminopropyl trimethyl polysiloxan is preferably present in weight ratio from 7 to 10
The said polyurethane dispersion grafted aminopropyltrimethylpolysiloxane [Z] (G-PUD) is having molecular weight in the range of 15240 to 17000 with 10 end terminals to attach the oxygen present on the surface of steel substrate and chemical structure is as shown in the reaction scheme. The said polyurethane based coating composition has the fluid and film properties as shown the table 1 below

The water borne polyurethane based coating as per the current invention can be applied using known methods such as wiping, brushing, spraying and dipping
In an embodiment of the invention, the borne polyurethane based coating is preferably applied by spraying method The coating is cured within 30 minutes at a temperature of 27°C and forms a dense structure of coating The dense polymer matrix provides excellent impermeability of corrosive ions (measured by polarization measurement) and water rolling effect with reduced surface tension.

Examples: Polyurethane based coating dispersion was combined with varying proportions of aminopropyl trimethyl polysiloxane to assess the effectiveness on galvanized steel surface in terms of corrosion resistance, water rolling effect etc. Table 1 illustrates the different type of coatings that were tested and evaluated as per the current invention,
t
The said Galvanized steel with zero spangled is of 0 55mm thickened It's measured corrosion rate and Corrosion density was found to be around 0 144 mm/year and 963E-06 A/cm2 respectively at -1 00 volt.
The table 3 shows below the corrosion resistance performance of different coatings as per table 2 that were tested as per the current invention



As evident from the table 3, all coating examples inventions are showing good hydrophobicity but among all the examples, PUD-9A (Example 7), PUD-10A (Example 8) and PUD-8A (example 6) is showing good properties respectively in terms of anticorrosion (Figure 2a and 2b) and water rolling effect with reduced surface tension of solution on GI (Table 4), as to evident by polarization study and contact angle measurement respectively The lower rolling effect depicts higher corrosion rate because of the high-water permeability.
Tafel Test:
Tafel test was performed using one coat of the coating shown in table 2 From figure 1 a and lb and 1C, and table 3, it was found that Examples 6 to 8 exhibited excellent corrosion resistance as compare to Example 1 to 5 Among the Examples 6 to 8, Example 7 was showing low corrosion rate All examples are showing lower corrosion rate as compare to uncoated GI as shown in Fig
2c
Contact angle and surface tension
The water rolling effect was measured by contact angle measurement using SURFTENS 4 5 software It is measure a contact angle of water drop on the sample. Good water rolling on surface is a result of high contact angle. The test was conducted only using coated samples as they have shown the good hydrophobicity It was observed that the contact angle for high concentrated grafted PUD (Examples 6 to 8) coated sample is more than the other samples, Also, the surface

energy of examples 6 to 8 was found to be lower than the other coated GI samples. So, Example
7(105.2°), Example 8(101 8°) and Example 6(100 1°) were showing good hydrophobicity respectively as shown in Table 3 and 4.

Sequence of hydrophobicity
Example 7(PUD-9A) > Example 8 (PUD-10A) > Example 6 (PUD-8A) > Example 1 (PUD) > Example 3 (PUD-5A) > Example 4 (PUD-6A) > Example 5 (PUD-7A) > Example 2 (PUD-4A)
The coatings as per the current invention can be used for coating metallic substrate used in construction sectors like AC cabinet, fridge body panel, roofing (structural application). Also, it can be applicable in plumbing (GI pipes) and threaded part of GI pipes where the zinc part has been removed It can be a substitute of metallic zinc coating This coating provides high gloss which is useful for marine applications The coating is particularly useful for coating the steel articles that are exposed to are into watery or alkali or humidified conditions.

WE CLAIM
1 A water borne polyurethane based coating composition prepared by combining:
a polyurethane dispersion with:
4 to 10 wt % of aminopropyl trimethyl polysiloxane,
2 The water borne polyurethane based coating composition as claimed in claim 1, wherein said polyurethane dispersion (PUD) is synthesized by taking mixture of 64 wt % of polyurethane resin (15000-16000gm molecular weight) and 2 mg KOH/g acid value, 32 wt. % of demoralized water into a reaction vessel and heating for an hour at 60°C with a continuous passing of argon gas and then keeping the vessel for cooling.
3 The water borne polyurethane based coating composition as claimed in claim 2, wherein the polyurethane dispersion further comprises 1 wt% of ethyl tri-ethoxy silane, 0 5 wt % of silicon based flow additive and 2 5 wt. % of zinc phosphate based rust inhibitor
4. The water borne polyurethane based coating composition as claimed in claim 2, wherein the polyurethane dispersion is having at least one functional group of -N-H- with -0-C=0 and represented by formula [-OOCNH-R1-NHCOO-R2-]
Where R1 is C5 to C40 containing cyclohexyl/tricyclononane structure;
And R2 is C6 to C40 containing cyclopentyl/ethylene biscyclopentyl structure
5 The water borne polyurethane based coating composition as claimed in claim 3, wherein silicon based flow additive is a solution of a polyether siloxane
6. The water borne polyurethane based coating composition as claimed in claim 3, wherein zinc phosphate based rust inhibitor is having the formula CaHO8PSiSrZn.

7. The water borne polyurethane based coating composition as claimed in claim 1, wherein Aminopropyl trimethyl polysiloxane is synthesized by hydrolysis and condensation of aminopropyl ethoxy dimethoxy si lane and aminopropyl butoxyethoxymethoxy si lane.
8 The water borne polyurethane based coating composition as claimed in claim 7, wherein synthesis of Aminopropyl trimethyl polysiloxane comprises mixing of 5 weight% aminopropyl ethoxy dimethoxy silane and 5 wt % of methyl butoxyethoxymethoxy silane in presence of 0 001 wt % of acetic acid in 90 wt. % of demineralized water.
9 The water borne polyurethane based coating composition as claimed in claim 7, wherein Aminopropyl trimethyl polysiloxan is represented by formula:

10. The water borne polyurethane based coating composition as claimed in claim I, wherein Aminopropyl trimethyl polysiloxan is preferably present in weight ratio from 7 to 10,
11 An article coated as per the water borne polyurethane based coating composition as claimed in claim 1.
12, The water borne polyurethane based coating composition as claimed in claim 1, wherein the coating is curable within one hour at 27oC.

13 The water borne polyurethane based coating composition as claimed in claim 1, wherein
thickness of the coating in dried form varies in the range of 20 m to 25 m
14 The water borne polyurethane based coating composition as claimed in claim 1, wherein
thickness of the coating in dried form is preferably 22 m.