Description:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a process of incorporation of Tannic Acid in Alkyd resin system and an anti-corrosive coating formulation using said Tannic Acid incorporated modified Alkyd resin system to enhance metal protection.

BACKGROUND OF THE INVENTION
For protection of metal against corrosion, application of coating on metal is most common technique. The coating layer protects the metal substrate as barrier with corrosion inhibitive pigments like zinc chromate, zinc tetroxychromate, lead chromate and zinc phosphate in suitable resin matrix. Due to the high toxicity of chromate pigments, there is a demand for green alternative to impart anticorrosive function in organic coating.

Tannic acid is one of the most interesting materials which are obtained from plants. Natural tannin is mostly made up of natural phenolic compounds which are found in the bark as well as wood [Shirmohammadli Y., Efhamisisi D., Pizzi A., Tannins as a sustainable raw material for green chemistry: A review, Industrial Crops & Products, 126 (2018) 316 – 332]. Tannic acid is water soluble high molecular weight polyphenolic compound with abundant terminal phenolic hydroxyl groups.

Tannins are generally available as condensed/hydrolysable forms (Fig. 1) [Aroso, I. M., Araujo, A. R., Pires, R. A., Reis, R.L., Cork: Current Technology Developments and Future Perspectives of the Natural, Renewable, and Sustainable Material. ACS Sustain. Chem. Eng. 5 (2017) 11130-11146, Mueller-Harbey, I., Analysis of hydrolysable tannins. Anin. Feed SCI. Technol. 91 (2001) 3-20]. It has a complex macromolecular structure of gallotannin, in which one glucose molecule bonded to five molecules of di-gallic acid units (Fig. 2).

Gallic acid Ellagic acid
Fig.1 Chemical structure of hydrolysable tannin Fig. 2 Chemical structure of tannin

Martinez et. al. reported that tannic acid acts as corrosion inhibitors due to physical or chemical adsorption on iron metal surface through free electron pair from the hydroxyl functional group (-OH), present in poly phenols. Such type of insoluble ferric complex acts as a barrier against oxygen diffusion and form protective film [Gust, J., Suwalski, J., Use of Mossbauer spectroscopy to study reaction products of Polyphenols and iron compounds, Corrosion 50 (1994) 355 – 365; Martinez, S., Inhibitory mechanism of mimosa tannin using molecular modeling and substitutional adsorption isotherms, Mater. Chem. Physis. 77 (2003) 97- 102; Martinez, S., Stern, I., Inhibitory mechanism of low – carbon steel corrosion by mimosa tannin in sulphuric acid solutions, J. Appl. Electro chem. 31 (2001) 973 – 978]. Zmozinski et. al. reported that the addition of complexing metals of zinc and magnesium with tannin into epoxy paint formulation enhances the anticorrosive performance of coating [Ariane V. Zmozinski, Rafael S. Peres, Kelly Freiberger, Carlos A. Ferreira, Silvia Margonei Mesquita Tamborim, Denise S. Azambuja, Zinc tannate and magnesium tannate as anticorrosion pigments in epoxy paint formulations Prog. Org. coat. 121 (2018) 23 -29]. Alessandro et. al. showed that tannic based primer coating performs excellent adhesion and barrier properties when applied on rusted steel surface [C. Byrne, O. D’Alessandro, G.J. Selmi, R. Romagnoli, C. Deya Primer based on tara and quebrachotannins for poorly prepared steel surfaces, Prog. Org. coat. 130 (2019) 244 – 250]. The presence of aromatic rings having hydroxyl groups in ortho position of tannin are used to form chelate with iron and other metallic cation. In case of Fe (III), a dark blue, highly insoluble complex ferric titanate is formed [Iglesias, J., Garcia de Saldana, E., Jaen, J. A., On the tannic acid interaction with metallic iron, Hyperfine Interact. 134 (2001) 109 – 114; Jaen, J. A., Deobaldia, J., Rodriguez, M. V., Application of Mossbauer Spectroscopy to the study of Tannins inhibition of Iron and Steel corrosion, Hyperfine Interact. 202 (2011) 25 – 38; Yahya, S., Shah, A. N., Rahim, A. A., Abd Aziz, N.H., Roslan, R., Phase transformation of rust in presence of various tannins, J. Phys. Sci. 19 (2008) 31 – 41; Deslauries, P. J., Rust conversion coatings, Mater. Perform. 26 (1987) 35 - 40].

However, most of the techniques for incorporation of tannin in coating system are of physical mixing of tannin or modified tannin into the resin matrix of coating system. Such type of coating system can only be used for temporary protection of metal against corrosion.

Tomita and Yonezawa reported the epoxidation of gallic acid with epichlorohydrin for use in adhesive application [Mashouf Roudsari, G., Mohanty, A. K., Misra, M., Green Approaches to engineer tough biobased epoxies: review. ACS Sustain. Chem. Eng. 5 (2017) 9528 - 9541]. The major limitation for use of such resin system in coating application is due to fast curing of epoxy tannin system without using hardener. Tannin based polyurethane surface coating have also been reported by Pizzi et. al. [Pizzi, A., Tannin – based polyurethane adhesives. J. Appl. Polym. Sci. 23 (1979a.) 1889 -1890]. However, such epoxidized tannin is of very fast reactive which is not suitable for use in coating application to deliver the properties like adhesion on substrate, flexibility, and hardness of coating film.

Interestingly, Flores et. al. studied the incorporation of tannin in primer formulation applied on rusted steel and an alkyd resin-based topcoat was applied on the primed surface. Such combined system performed better anticorrosive performance compared to waterborne tannin in primer formulation or pure alkyd-based coating system [Flores Merino, S., Caprari, J., Vasqueztorres, I., Figucroa Ramos, I., Hadzich Grola, A., Inhibitive action of tara tannin in rust converter formulation, Anti -corrosion Methods Mater. 64 (2017) 136 -147]. Marinko et. al. investigated the incorporation of modified tannin in alkyd resin after combining two separate components. In one part, tannin was modified after incorporation of nitrogen functionalities within tannin structure by reaction with ammonium hydroxide/poly amine like diethylene tri amine. In second part, tannin was epoxidized with epichlorohydrin followed by reaction with linseed fatty acid. After mixing of these two parts – tannin modified alkyd system was formed. However, such process technology for modification of tannin is very complex for synthesis.

Further, attempts to incorporate tannic acid in alkyd formulation resulted in serious problem of polymer incompatibility. This led to phase separation and consequently slow release of tannic acid from coating film on exposure to environment, resulting in loss of anticorrosive performance as well as durability properties of coating film. This is due to the difference in polarity of the two polymers. Tannic acid is highly polar but less reactive towards different alkyd components. As a result, it is very difficult to form a single-phase material of tannic acid in alkyd system.

The process of incorporation of tannic acid in coating formulation is by physical mixing of tannic acid with resin system, has limitation for achieving long term performance of anti-corrosive property. Hence, there is an imperative need to a novel approach for incorporation of tannic acid in resin system by chemical modification, so that the modified resin is suitable for coating application. Alkyd resin is the largest volume of resin used in paint industry due to its low cost, formulation flexibility and wide spectrum of application for both in decorative as well as industrial coating. The major limitation for use of alkyd is inferior performance with respect to moisture permeability leads to poor anti corrosive performance under salts in water environment.

Although to perform anticorrosive properties of coating by using tannic acid is well known by physical mixing of tannic acid in coating formulation, but this process has limitation for long time protection of metal against corrosion. Incorporation of tannic acid moiety in alkyd chain through chemical modification is challenging. In this investigation, this challenge has been overcome by incorporation of tannic acid in alkyd chain after chemical modification of tannic acid through a novel route as well as achievement of long term anti corrosive performance of coating film based on tannic acid modified alkyd which has not been reported earlier. Such modified alkyd resin may increase the usefulness of alkyd in versatile application like protective as well as decorative coating.

OBJECT OF THE INVENTION
It is main object of present invention to provide a process of incorporation of Tannic Acid in Alkyd resin system and to develop an anti-corrosive coating formulation using said Tannic Acid incorporated modified Alkyd resin system for long term metal protection.

SUMMARY OF THE INVENTION
The following disclosure presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

One aspect of present invention relates to a process of incorporation of Tannic Acid in Alkyd resin system to be used in an anti-corrosive formulation, comprising:
i. chemical modification of tannic acid with formaldehyde for methylol functionalization in tannic acid moiety;
ii. chemical modification of methylol functionalized tannic acid with rosin ester to form chroman derivatives via quinone methides formation;
iii. chemical modification of chroman derivative of rosin ester and tannic acid with alkyd resin to form tannic acid modified alkyd resin.

In an embodiment of present invention, said step (i) chemically modifying tannic acid with formaldehyde for methylol functionalization in tannic acid moiety comprises:
(a) mixing of 1-12 wt. % powder tannic acid, 0.1-2 wt. % paraform, 5-25 wt. % solvent 2-Ethoxy Ethanol and 0.01-0.2 wt. % oxalic acid (as catalyst) in a glass reactor fitted with mechanical stirrer, thermometer, and air condenser and
(b) heating said reactor around 80 – 900C and holding at this temperature for 30 min. to form a clear mass.

In another embodiment of present invention, said step (ii) chemically modifying said methylol functionalized tannic acid obtained in step (i) with rosin ester to form chroman derivatives via quinone methides formation comprises:
(c) mixing 1-12 wt. % of rosin ester in 2-12 wt. % xylene and 2-Ethoxy Ethanol solvent mixture followed by heating at a 70 – 800 C and holding at this temperature till to form a clear solution of rosin ester;
(d) adding 2-20 wt. % of the clear rosin ester solution obtained in sub-step (c) slowly into the reactor containing methylol functionalized tannic acid obtained in substep (b) of step (i) under stirring at a temperature of 80 – 900C; and
(e) heating the reactor up to 120 – 1250C and holding for 15 – 20 minutes to form a clear mass.

In a further embodiment, said xylene and 2-Ethoxy Ethanol are mixed in sub-step (c) in a ratio 2:1 by wt.

According to another embodiment of present invention, said step (iii) chemically modifying said chroman derivative of rosin ester and tannic acid obtained in step (ii) with alkyd resin to form tannic acid modified alkyd resin comprises:
(f) preparing a soyabean oil fatty acid based alkyd resin;
(g) thinning the prepared alkyd of sub-step (f) in xylene solvent.
(h) adding the clear solution of chroman derivative of tannic acid and rosin ester obtained in sub-step (e) slowly to the prepared alkyd of sub-step (g) under stirring at a temperature of 120 – 130 0C and holding at this temperature for around 2 hrs. for chemical modification of rosin ester and tannic acid with alkyd resin.

In a further embodiment, said sub-step (f) preparing a soyabean oil fatty acid based alkyd resin comprises:
(fa) taking vegetable oil fatty acid, polyol and polybasic acid in a reactor equipped with a mechanical stirrer, a condenser attached with a Dean and Stark apparatus, a thermometer;
(fb) charging an azeotropic solvent xylene into reaction mixture of step (fa) to remove water, formed during esterification reaction; wherein the azeotropic distillation was started at a temperature of 1600C and the reaction mixture temperature was increased to 2300C at a rate of 100C per hr;
(fc) continuing the reaction of step (fb) at 2300C till acid value attained below 10 mg-KOH per gm.

Another aspect of present invention relates to modified Alkyd resin system comprising 16 – 25 wt. % soya fatty acid, 8 – 15 wt. % pentaerythritol, 10 – 18 wt. % phthalic anhydride and 7 – 45 wt. % modified tannic acid -rosin ester adduct obtained from the process as disclosed above.

Another aspect of present invention relates to an anti-corrosive coating formulation; comprising 1 – 3 wt. % rutile, 6 – 12 wt. % red iron oxide as pigment, 5 – 9 wt. % silica, 2 – 4 wt. % talc, 6 – 10 wt. % whiting, 15 – 25 wt. % calcium carbonate, 4 – 6 wt. % china clay as extender, 0.2 – 0.6 wt. % different additives like wetting and dispersing agent, 0.2 – 0.6 wt. % bentonite clay as thixotropic agent, 0.5 – 1.5 wt. % anti-skinning agent, driers along with different solvents like xylene, solvent C 9, 2-Ethoxy Ethanol and modified Alkyd resin binder obtained from the process as disclosed above.

Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above and other aspects, features and advantages of the embodiments of the present disclosure will be more apparent in the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 illustrates schematic presentation for preparation of tannic acid rosin ester modified alkyd as disclosed in one of the embodiments.

Figure 2 illustrates FTIR absorption spectra of unmodified tannic acid (A), modified tannic acid (B), modified tannic acid and rosin ester adduct (C) and tannic acid rosin ester adduct modified alkyd (D) as disclosed in the embodiments of present invention.

Figure 3 illustrates different paint coated panels after 400 hrs salt spray exposure. (A) Paint based on unmodified alkyd, (B) Paint based on 1.5 % Tannic Acid modified alkyd, (C) Paint based on 3 % Tannic Acid modified alkyd, (D) Paint based on 6 % Tannic Acid modified alkyd (E) Paint based on 9 % Tannic Acid modified alkyd, and (F) Paint based on 3 % Tannic Acid and 2.8 % Rosin ester mixture in alkyd.

Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may not have been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding, but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments belong. Further, the meaning of terms or words used in the specification and the claims should not be limited to the literal or commonly employed sense but should be construed in accordance with the spirit of the disclosure to most properly describe the present disclosure.

The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising" used herein specify the presence of stated features, integers, steps, operations, members, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, components, and/or groups thereof.

The present disclosure will now be described more fully with reference to the accompanying drawings, in which various embodiments of the present disclosure are shown.

In one embodiment present invention relates to a process of incorporation of Tannic Acid in Alkyd resin system to be used in an anti-corrosive coating formulation, comprising:
i. chemical modification of tannic acid with formaldehyde for methylol functionalization in tannic acid moiety;
ii. chemical modification of methylol functionalized tannic acid with rosin ester to form chroman derivatives via quinone methides formation;
iii. chemical modification of chroman derivative of rosin ester and tannic acid with alkyd resin to form tannic acid modified alkyd resin.

In an embodiment of present invention, said step (i) chemically modifying tannic acid with formaldehyde for methylol functionalization in tannic acid moiety comprises:
(a) mixing of 1-12 wt. % powder tannic acid, 0.1-2 wt. % paraform, 5-25 wt. % solvent 2-Ethoxy Ethanol and 0.01-0.2 wt. % oxalic acid (as catalyst) in a glass reactor fitted with mechanical stirrer, thermometer, and air condenser and
(b) heating said reactor around 80 – 900C and holding at this temperature for 30 min. to form a clear mass.

In another embodiment of present invention, said step (ii) chemically modifying said methylol functionalized tannic acid obtained in step (i) with rosin ester to form chroman derivatives via quinone methides formation comprises:
(c) mixing of 1-12 wt. % rosin ester in 2-12 wt. % xylene and 2-Ethoxy Ethanol solvent mixture followed by heating at a 70 – 800 C and holding at this temperature till to form a clear solution of rosin ester;
(d) adding 2-20 wt. % of clear rosin ester solution obtained in sub-step (c) slowly into the reactor containing methylol functionalized tannic acid obtained in sub-step (b) of step (i) under stirring at a temperature of 80 – 900C; and
(e) heating the reactor up to 120 – 1250C and holding for 15 – 20 minutes to form a clear mass.

In a further embodiment, said xylene and 2-Ethoxy Ethanol are mixed in sub-step (c) in a ratio 2:1 by wt.

According to another embodiment of present invention, said step (iii) chemically modifying said chroman derivative of rosin ester and tannic acid obtained in step (ii) with alkyd resin to form tannic acid modified alkyd resin comprises:
(f) preparing a soyabean oil fatty acid based alkyd resin;
(g) thinning the prepared alkyd of sub-step (f) in xylene solvent.
(h) adding the clear solution of chroman derivative of tannic acid and rosin ester obtained in sub-step (e) slowly to the prepared alkyd of sub-step (g) under stirring at a temperature of 120 – 130 0C and holding at this temperature for around 2 hrs for chemical modification of rosin ester and tannic acid with alkyd resin.

In a further embodiment, said sub-step (f) preparing a soyabean oil fatty acid based alkyd resin comprises:
(fa) taking vegetable oil fatty acid, polyol and polybasic acid in a reactor equipped with a mechanical stirrer, a condenser attached with a Dean and Stark apparatus, a thermometer;
(fb) charging an azeotropic solvent xylene into reaction mixture of step (fa) to remove water, formed during esterification reaction; wherein the azeotropic distillation was started at a temperature of 1600C and the reaction mixture temperature was increased to 2300C at a rate of 100C per hr;
(fc) continuing the reaction of step (fb) at 2300C till acid value attained below 10 mg-KOH per gm.

Another aspect of present invention relates to modified Alkyd resin system comprising 16 – 25 wt. % vegetable oil fatty acid, 8 – 15 wt. % polyol, 10 – 18 wt. % polybasic acid and 7 – 45 wt. % modified tannic acid -rosin ester adduct obtained from the process as disclosed above.

In an embodiment, said vegetable oil fatty acid is soya fatty acid, said polyol is pentaerythritol and said polybasic acid is phthalic anhydride.

Another aspect of present invention relates to an anti-corrosive coating formulation; comprising 1 – 3 wt. % rutile, 6 – 12 wt. % red iron oxide as pigment, 5 – 9 wt. % silica, 2 – 4 wt. % talc, 6 – 10 wt. % whiting, 15 – 25 wt. % calcium carbonate, 4 – 6 wt. % china clay as extender, 0.2 – 0.6 wt. % different additives like wetting and dispersing agent, 0.2 – 0.6 wt. % bentonite clay as thixotropic agent, 0.5 – 1.5 wt. % anti-skinning agent, driers along with different solvents like xylene, solvent C 9, 2-Ethoxy Ethanol and modified Alkyd resin binder obtained from the process as disclosed above.

Different embodiments of present invention could be better understood with the help of few examples provided below:

EXAMPLE 1
Tannic acid modified alkyd composition and Characterization
The chemical modification of tannic acid is carried out by mixing of powder tannic acid, paraform, solvent 2-Ethoxy Ethanol and oxalic acid (as catalyst) in a glass reactor fitted with mechanical stirrer, thermometer, and air condenser. The reactor is heated around 80 – 900C and hold at this temperature for 30 min. to form a clear mass

To form chroman derivative of rosin ester and methylol functionalized tannic acid, the following steps are involved
(a) a clear solution of rosin ester is made in a solvent mixture of xylene and 2-Ethoxy Ethanol (2:1 by wt.) separately by heating at a 70 – 800 C and hold at this temperature till to form a clear solution.
(b) The clear rosin ester solution is slowly added into the reactor containing methylol functionalized tannic acid under stirring at a temperature of 80 – 900C. After complete addition, the reactor is heated up to 120 – 125 0C and hold for 15 – 20 minutes to form a clear mass.

For incorporation of chroman derivative of rosin ester-tannic acid in alkyd resin, the following steps are involved.
(a) soyabean oil fatty acid based alkyd resin was prepared by taking vegetable oil fatty acid, polyol and polybasic acid in a reactor equipped with a mechanical stirrer, a condenser attached with a Dean and Stark apparatus, a thermometer. The azeotropic solvent xylene was charged into reaction mixture to remove water, formed during esterification reaction. The azeotropic distillation was started at a temperature of 1600C and the reaction mixture temperature was increased to 2300C at a rate of 100C per hr. The reaction was continued at 2300C till acid value attained below 10 mg-KOH per gm. Finally, the prepared alkyd was thinned in xylene solvent.
(b) The clear solution of chroman derivative of tannic acid and rosin ester is slowly added to the prepared alkyd under stirring at a temperature of 120 – 130 0C and hold at this temperature for around 2 hrs. for chemical modification of rosin ester and tannic acid with alkyd resin.

Composition of tannic acid modified alkyd at different tannic acid concentration is presented in Table 1

Table 1 Composition of tannic acid modified alkyd at different tannic acid content
Alkyd Ingredients Alkyd I Alkyd II Alkyd III Alkyd IV
Soya fatty acid 24.24 22.99 20.31 17.34
Pentaerythritol 13.48 12.78 11.29 9.64
Phthalic anhydride 17.10 16.22 14.33 12.24
xylene 31.61 30.05 22.84 21.76
2-Ethoxy Ethanol 10.50 11.81 18.95 20.61
Tannic acid 1.50 3.00 6.00 9.00
Paraform (92%) 0.18 0.36 0.72 1.08
Oxalic acid 0.02 0.04 0.08 0.11
Rosin ester 1.37 2.75 5.48 8.22
Total 100.00 100.00 100.00 100.00

Fig. 2 FTIR illustrates absorption spectra of unmodified tannic acid (A), modified tannic acid (B), modified tannic acid and rosin ester adduct (C) and tannic acid rosin ester adduct modified alkyd (D). In the FTIR spectra, the presence of sharp characteristic peak at 3400 cm -1 is due to OH stretch, 1022 cm -1 C-O stretch, 1444 cm -1 C=C stretch in aromatic ring, 1585 cm -1 C=C stretch in aromatic ring of tannic acid (Fig. 2A). After reaction of formaldehyde with tannic acid, methylol groups (-CH2OH groups) are formed which indicates the formation of broad absorption spectra at 3200 - 3500 cm-1 as well as appearance of absorption peak at 2924 cm -1 (-CH2- stretch) clearly indicates the formation of methylol substituent in tannic acid moiety (Fig. 2B). After reaction of rosin ester with tannic acid the broadness of absorption spectra of – OH functional group disappear to some extent as well as the formation of characteristic absorption peak at 1226 cm-1 corresponds to cyclic ether (chroman ring structure) in tannic acid and rosin ester adduct (Fig. 2C). The significant absorption bands i. e. at 1240, 1726, 2855 and 2925 cm-1 confirm the modification of tannic acid and rosin ester adduct in alkyd resin matrix (Fig. 2D).

For evaluation of anti-corrosive performance of tannic acid modified alkyd resin in paint, the paint was prepared by mixing alkyd resin and other paint ingredients in bead mill using zirconium beads and run for 1 hr. to achieve grinding of below 25 microns as per standard process of paint preparation. A composition of paint is presented in Table 2

Table 2 Composition of paint
Paint ingredients Quantity in wt. %
Alkyd resin 22 - 28
Wetting agent 0.2 – 0.6
Bentonite Clay 0.2 – 0.8
Red Iron Oxide 6 - 12
Titanium dioxide 1 - 3
Calcium Carbonate 15 - 25
China Clay 4 - 6
Silica 5 - 9
Whiting 6 - 10
Talc 2 - 4
Anti-skinning agent 0.5 – 1.5
Xylene 12 - 16
Solvent C 9 2 - 6
2-Ethoxy Ethanol 2 - 7
Mn octoate 0.2 – 0.8
Zr octoate 0.2 – 0.8
Co octoate 0.2 – 0.8

The anti-corrosive performance of coating film by salt spray test of tannic acid modified alkyd resin based coating was evaluated as per ASTM B117. After 400 hrs. of exposure, coatings were assessed in accordance with ASTM D 610-08 for blisters near the scribe appeared. Fig. 3, shows the images of tested panels after salt spray test. Figure 3 clearly indicates that tannic acid-based coating showed better corrosion resistance than coating with unmodified alkyd based coating as well as tannic acid and rosin ester mixed alkyd based coating.

EXAMPLE 2
Effect of tannic acid modification into alkyd resin on anti-corrosive performance of paint
To investigate the effect of tannic acid modification in alkyd resin system, tannic acid was used in alkyd resin as a physical mixture without any chemical modification followed by preparation of paint with alkyd tannic acid mixture. The alkyd composition along with tannic acid and rosin ester as mixture is presented in Table 3.

Table 3 Alkyd composition containing tannic acid as mixture
Alkyd Ingredients Quantity in wt. %
Soya fatty acid 31.37
Pentaerythritol 17.44
Phthalic anhydride 22.13
Xylene 17.06
Tannic acid 3.00
Rosin ester 2.80
2-Ethoxy Ethanol 5.80
Paraform (92 %) 0.36
Oxalic acid 0.04
Total 100.00

The anti-corrosive performance of paint film was performed after preparation of paint using alkyd composition as presented in Table 3 and as per paint formulation presented in Table 2.

The anti-corrosive performance of coating film by salt spray test was evaluated as per ASTM B117. After 400 hrs. of exposure, coatings were assessed in accordance with ASTM D 610-08 for blisters near the scribe appeared. Fig. 3, shows the images of tested panels after salt spray test. Figure 3 clearly indicates that tannic acid modified alkyd based coating showed better corrosion resistance than coating with tannic acid as physical mixture in alkyd based coating.

EXAMPLE 3
Effect of tannic acid into alkyd resin on anti-corrosive performance of paint
To study the effect of tannic acid in alkyd resin system, an alkyd resin was synthesized without using tannic acid in alkyd formulation followed by preparation of paint with the alkyd. The alkyd composition without using tannic acid and rosin ester is presented in Table 4.

Table 4 Alkyd composition without tannic acid and rosin ester
Alkyd Ingredients Quantity in wt. %
Soya fatty acid 25.40
Pentaerythritol 14.12
Phthalic anhydride 17.92
Xylene 30.58
Tannic acid -
Rosin ester -
2-Ethoxy Ethanol 11.98
Paraform (92 %) -
Oxalic acid -
Total 100.00

The anti-corrosive performance of paint film was performed after preparation of paint using alkyd composition as presented in Table 4 and as per paint formulation presented in Table 2.

The anti-corrosive performance of coating film by salt spray test was evaluated as per ASTM B117. After 400 hrs. of exposure, coatings were assessed in accordance with ASTM D 610-08 for blisters near the scribe appeared. Fig. 3, shows the images of tested panels after salt spray test. Figure 3 clearly indicates that the coating film without tannic acid based alkyd is much inferior with respect to anti-corrosive performance than coating based on tannic acid modified alkyd.

Mechanical properties of different coating film with respect to cross-cut adhesion was performed as per ASTM D-3359-95a. The test results are presented in Table 5.
Table 5 Adhesion test results of different coating film
Coating film reference Cross cut adhesion, %
Coating film based on 1.5 % Tannic Acid modified alkyd 100
Coating film based on 3.0 % Tannic Acid modified alkyd 100
Coating film based on 6.0 % Tannic Acid modified alkyd 70
Coating film based on 9.0 % Tannic Acid modified alkyd 75
Coating film based on alkyd with Tannic Acid as mixture 50
Coating film based on alkyd without Tannic acid Fails

From adhesion test data it is evident that tannic acid modification up to 3 % in alkyd resin is optimum to achieve satisfactory results. Higher loading of tannic acid modification in alkyd results brittleness property in coating film.
, Claims:
1. A process of incorporation of Tannic Acid in Alkyd resin system to be used in an anti-corrosive coating formulation, comprising:
i. chemically modifying tannic acid with formaldehyde for methylol functionalization in tannic acid moiety;
ii. chemically modifying said methylol functionalized tannic acid obtained in step (i) with rosin ester to form chroman derivatives via quinone methides formation; and
iii. chemically modifying said chroman derivative of rosin ester and tannic acid obtained in step (ii) with alkyd resin to form tannic acid modified alkyd resin.

2. The process as claimed in claim 1, wherein said step (i) chemically modifying tannic acid with formaldehyde for methylol functionalization in tannic acid moiety comprises:
(a) mixing of 1-12 wt. % powder tannic acid, 0.1-2 wt. % paraform, 5-25 wt. % solvent 2-Ethoxy Ethanol and 0.01-0.2 wt. % oxalic acid (as catalyst) in a glass reactor fitted with mechanical stirrer, thermometer, and air condenser and
(b) heating said reactor around 80 – 900C and holding at this temperature for 30 min. to form a clear mass.

3. The process as claimed in claim 1, wherein said step (ii) chemically modifying said methylol functionalized tannic acid obtained in step (i) with rosin ester to form chroman derivatives via quinone methides formation comprises:
(c) mixing 1-12 wt. % of rosin ester in 2-12 wt. % xylene and 2-Ethoxy Ethanol solvent mixture followed by heating at a 70 – 800 C and holding at this temperature till to form a clear solution of rosin ester;
(d) adding 2-20 wt. % of the clear rosin ester solution obtained in sub-step (c) slowly into the reactor containing methylol functionalized tannic acid obtained in sub-step (b) of step (i) under stirring at a temperature of 80 – 900C; and
(e) heating the reactor up to 120 – 1250C and holding for 15 – 20 minutes to form a clear mass.

4. The process as claimed in claim 3, wherein said xylene and 2-Ethoxy Ethanol are mixed in sub-step (c) in a ratio 2:1 by wt.

5. The process as claimed in claim 1, wherein said step (iii) chemically modifying said chroman derivative of rosin ester and tannic acid obtained in step (ii) with alkyd resin to form tannic acid modified alkyd resin comprises:
(f) preparing a soyabean oil fatty acid based alkyd resin;
(g) thinning the prepared alkyd of sub-step (f) in xylene solvent.
(h) adding the clear solution of chroman derivative of tannic acid and rosin ester obtained in sub-step (e) slowly to the prepared alkyd of sub-step (g) under stirring at a temperature of 120 – 130 0C and holding at this temperature for around 2 hrs for chemical modification of rosin ester and tannic acid with alkyd resin.

6. The process as claimed in claim 5, wherein said sub-step (f) preparing a soyabean oil fatty acid based alkyd resin comprises:
(fa) taking vegetable oil fatty acid, polyol and polybasic acid in a reactor equipped with a mechanical stirrer, a condenser attached with a Dean and Stark apparatus, a thermometer;
(fb) charging an azeotropic solvent xylene into reaction mixture of step (fa) to remove water, formed during esterification reaction; wherein the azeotropic distillation was started at a temperature of 1600C and the reaction mixture temperature was increased to 2300C at a rate of 100C per hr;
(fc) continuing the reaction of step (fb) at 2300C till acid value attained below 10 mg-KOH per gm.

7. A modified Alkyd resin system comprising 16 – 25 wt. % vegetable oil fatty acid, 8 – 15 wt. % polyol, 10 – 18 wt. % polybasic acid and 7 – 45 wt. % modified tannic acid -rosin ester adduct obtained from the process claimed in claims 1-3.

8. The modified Alkyd resin system as claimed in claim 7, wherein said vegetable oil fatty acid is soya fatty acid, said polyol is pentaerythritol and said polybasic acid is phthalic anhydride.

9. An anti-corrosive coating formulation comprising 1 – 3 wt. % rutile, 6 – 12 wt. % red iron oxide as pigment, 5 – 9 wt. % silica, 2 – 4 wt. % talc, 6 – 10 wt. % whiting, 15 – 25 wt. % calcium carbonate, 4 – 6 wt. % china clay as extender, 0.2 – 0.6 wt. % different additives like wetting and dispersing agent, 0.2 – 0.6 wt. % bentonite clay as thixotropic agent, 0.5 – 1.5 wt. % anti-skinning agent, driers along with different solvents like xylene, solvent C 9, 2-Ethoxy Ethanol and modified Alkyd resin binder obtained from the process as claimed in claims 1-6.