Title of Invention	A CORROSION RESISTANT POLYANILINE (PANI) CONTAINING PAINT FOR CORROSION PREVENTION OF STEEL SURFACES AND A PROCESS FOR PREPARING THE SAID PAINT
Abstract	In the present invention there is provided a corrosion resistant non toxic paint containing conducting polyaniline (pani) with a vinyl binder and solvent, having good adhesion and sufficient thickness, for corrosion protection of steel surfaces in acid and saline environment and a process for preparing the said paint. The corrosion resistant property of the coating formed by the developed paint has been evaluated by immersion test, potential measurements and impedance test in 3 % NaCI and by salt spray test.

Title of Invention

A CORROSION RESISTANT POLYANILINE (PANI) CONTAINING PAINT FOR CORROSION PREVENTION OF STEEL SURFACES AND A PROCESS FOR PREPARING THE SAID PAINT

Abstract

In the present invention there is provided a corrosion resistant non toxic paint containing conducting polyaniline (pani) with a vinyl binder and solvent, having good adhesion and sufficient thickness, for corrosion protection of steel surfaces in acid and saline environment and a process for preparing the said paint. The corrosion resistant property of the coating formed by the developed paint has been evaluated by immersion test, potential measurements and impedance test in 3 % NaCI and by salt spray test.

Full Text	The present invention relates to a corrosion resistant non-toxic paint containing conducting polyaniline (pani) for corrosion prevention of steel surfaces and process thereof The present invention particularly relates to a corrosion resistant conducting polyaniline (PANI) containing paint for corrosion prevention of steel surfaces and a process for preparing the said paint. The present invention more particularly relates to a corrosion resistant conducting polyaniline (PANI) containing paint with vinyl binder for corrosion prevention of steel surfaces and a process for preparing the said paint. The steel structures are coated by paint in order to prevent corrosion when exposed to atmosphere. Various primer coating systems based on paints containing pigments such as zinc phosphate, zinc chromate etc have been developed. Most of these coating systems contain toxic pigments and hence it is desirable to develop a coating system containing non-toxic pigment. In this regard, conducting polymer can be used as pigment by replacing the conventional toxic pigments used in paints. The new class of primers containing inherently conducting polymers, have got more tolerence to pin holes due to the passivating ability of pigments. It is reported [G. Mengoli, M. Munari, P. Bianco and M. Musiani, J. Appl. Polymer Sci., 26, 4247 (1982).] that polyaniline containing paints offer high corrosion resistant coatings. Santos etal [J.R. Santos.Jr., L.H.C. Mattoso and A.J. Motheo, Electrochimica Acta, 43, 309 (1998).] have studied the corrosion resistant property of steel coated with polyaniline by spraying a 2 % solution of polyaniline in N methyl pyrrolidine. They found that the steel coated with polyamine gained nearly 100 mV in corrosion potential in 3 % NaCI and a low corrosion rate was observed. This change in corrosion potential has been attributed due to the formation of a passivated layer. Further, these studies showed that the PAN I film loses water when kept out of the solution and returns to the original state after some time in contact with the solution without losing electrical and mechanical characteristics. This effect is probably due to the presence of air which keeps PAN I in the emaraldine oxidation state. Wessling etal [B. Wessling and J. Posdorfer, Electrochimica Acta, 44, 2139 (1999).] have studied the performance of polyaniline primer coatings on steel by salt spray test, electrochemical impedance spectroscopy and Scanning Kelvin-Probe in 3 % NaCI. They have found that the coating system with polyaniline primer has been found to be corrosion resistant. The polyaniline coating on steel is able to protect the scratches and pinholes present in the coating by the passivation of exposed areas [ W.K. Lu, R. L. Elsenbaumer and B. Wessiling, Synthetic Metals, 71, 2163 (1995) ]. However the coating is not of sufficient thickness in a single coat. The mechanistic investigation of polyaniline corrosion protection using scanning reference electrode technique has been made by Kinlen etal [P.J. Kinlen, V. Menon and Y. Ding, J. Electrochem. Soc., 146, 3690 (1999)]. They have found that polyaniline coatings passivate the pinhole defects in coatings. Further they have shown that phosphonic acid salts of polyaniline are more effective for corrosion protection than sulfonic acid salts. A model has been proposed for the protection of polyaniline coatings. In all the above studies it has been shown that the conducting polymer coating such as polyaniline stabilizes the potential of the metal in a passive region and maintain a protective oxide layer on the metal. Both SEM and XPS studies have revealed that an oxide layer has been formed between the PANI coating and the steel surface and is composed mainly of FeaOa above a very thin FesO4 layer [B. Wessling, Adv. Mater, 6, 226 (1994); A. Talo, P. Passiniemi, O. Forsen, S. Ylassari, Synth. Met, 85, 1333 (1997); B. Wessling, Synth. Met, 85, 1313 (1997)]. It has been reported by Wrobleski etal [D.A. Wrobleski, B.C. Benicewicz, K.G.Thompson and C.J. Bryan, Poly. Chem., 35, 265 (1994)] that the doped electrically conducting form of polyaniline film (film of thickness 0.005 cm) on steel with epoxy top coat gave excellent performance in 3.5 % NaCI and 0.1 M HCI even at scribed areas. However this coating is not adherent to the surface. The mechanism of protection of conducting polymer coating has been investigated by Jain etal [F.C. Jain, J.J. Rosato, K.S. Kalonia and V.S. Agarwala, Corrosion, 42, 700 (1986)]. It has been stated that the doped conducting polymer will generate an electric field that will restrict the flow of electrons from the metal to an outside oxidizing species thus preventing the corrosion. The corrosion resistance of PANI coatings on steel is also reported T.P.Me Andrew, A.G. Gilicinski and L.M.Robson, US Patent 5441772 (1995)]. However the studies on the anticorrosive properties of un doped polyaniline coated on mild steel have shown that the performance of PANI coated system is not good due to the poor adhesion [W.S. Araujo, I.C.P. Margarit, M. Ferreira, O.R. Mattos, P.Lima Neto, Electrochimica Acta, 46, 1307 (2001)]. In the review [T. P. Me Andrew, TRIP, 5, 7 (1997)] by Mcandrew has stated that the future for the use of electrically conducting polymers in corrosion resistant coatings appears promising, especially as additives to improve the performance of existing coating system. In a recent study [A. B. Samli, A. S. Pantekar, J. Rengarajan and P.C. Deb., Prog. Org. Coatings, 47, 1 (2003)], it is reported that the lower polyaniline loaded paint has been found to be more corrosion resistant. The use of such coatings in acid media is not estabilished. Hitherto it is reported in various patents the use of polyaniline in corrosion resistant coatings. Reference may be made to US patent No. 5,853,621 (Dt 29 Dec1998 by Miller etal) on "Corrosion resistant paint", which deals with the paint system containing non conducting conjugate polymers. Reference may be made to another US patent 6,054,514 (Dt25 Apr 2000 by Kulkarni etal) on "Additives for enhancing corrosion protection of metals", which deals with coating system containing polyaniline in acrylic binder resistant to neutral media. Reference may also be made to US patent 5,928,795 (Dt 27 July 1999 by Spellane etal), wherein is disclosed protective coatings with polyaniline to protect aluminium substrates. Reference may also be drawn to D.A. Wrobleski, B.C. Benicewicz, K.G.Thompson and C.J. Bryan, Poly. Chem., 35, 265 (1994); W.K. Lu, R. L. Elsenbaumer and B. Wessiling, Synthetic Metals, 71, 2163 (1995); A. B. Samli, A. S. Pantekar, J. Rengarajan and P.C. Deb., Prog. Org. Coatings, 47 ,1 (2003), and US Patent nos.: 5,853, 621 and 6, 054, 514. Hitherto it is reported that steel samples coated with polyaniline containing paint has been found to offer corrosion protection. The drawbacks of the coating reported are: (i) coatings have poor adhesioin; (ii) sufficient thickness can not be obtained in a single coat; (iii) corrosion protection in acid media is not established; (iv) the paints were formulated using PANI pigment and solvent without any binder; and (v) the paints were formulated with non conducting polyaniline pigment and conducting polyaniline pigment in acrylic binder for protection of steel in neutral media. The main objective of the present invention is to provide a corrosion resistant polyaniline (pani) containing paint for corrosion prevention of steel surfaces, which obviates the disadvantages of the hitherto known prior art. Another objective of the present invention is to provide a corrosion resistant non toxic conducting polyaniline (PANI) containing paint for corrosion prevention of steel surfaces. Still another objective of the present invention is to provide a corrosion resistant conducting polyaniline (PANI) containing paint with a vinyl binder for corrosion prevention of steel surfaces. Yet another objective of the present invention is to provide a process for preparing a corrosion resistant conducting polyaniline (pani) containing paint with vinyl binder for corrosion prevention of steel surfaces, which obviates the disadvantages of the hitherto known prior art. A further objective of the present invention is to provide a non toxic paint system containing conducting polyaniline with a vinyl binder, having good adhesion and sufficient thickness, for corrosion protection of steel surfaces in acid and saline environment and a process for preparing the said paint. In the present invention there is provided a corrosion resistant non toxic paint containing conducting polyaniline (pani) with a vinyl binder and solvent, having good adhesion and sufficient thickness, for corrosion protection of steel surfaces in acid and saline environment and a process for preparing the said paint. Accordingly, the present invention provides a corrosion resistant non-toxic paint containing conducting polyaniline (pani) for corrosion prevention of steel surfaces, which comprises non-toxic conducting polyaniline (pani) with a vinyl binder and solvent In an embodiment of the present invention, the vinyl binder is a vinyl resin of high molecular weight having average molecular weight of the order of 30,000. In another embodiment of the present invention, the vinyl binder is a vinyl resin such as vinyl acetate, vinyl chloride or mixture thereof. In still another embodiment of the present invention, the solvent is such as methyl isobutyl ketone. Accordingly, the present invention provides a process for preparing the above said corrosion resistant non toxic paint, which comprises: (i) preparing a conducting polyaniline (pani) by dissolving 0.8 to 1.2 M of distilled aniline in 0.8 to 1.2 M Hydrochloric acid, cooling the aniline and acid mixture to a temperature of 5° ± 1° C; adding pre-cooled 0.8 to 1.2 M ammonium persulphate solution drop wise to the said pre-cooled aniline and acid mixture for 1.5 hours under constant stirring, maintaining the reaction mixture at a temperature of 5° ± 1° C; continue the stirring for a further period of the order of 2 hours for ensuring complete polymersation; filtering to obtain a dark green coloured conducting polyaniline; washing repeatedly with distilled water to remove excess acid content; air drying for a few hours followed by oven drying at a temperature of 80° C for 2 hours; fine grinding the dried polyaniline; (ii) preparing a vinyl solution by adding solvent such as methyl isobutyl ketone (MIBK) to vinyl resin of high molecular weight having average molecular weight of the order of 30,000, such as vinyl acetate, vinyl chloride or mixture thereof, under constant slow stirring for a period of 24 hours for complete soubility; (iii) dispersing completely the dried polyaniline powder, obtained in step (i), in the said vinyl solution, obtained in step (ii), followed by adding MIBK solvent to obtain corrosion resistant paint. In an embodiment of the present invention, the molar concentrations of aniline, acid and ammonium persulphate are equal. The novelty of the present invention resides in providing a corrosion resistant non toxic paint containing conducting polyaniline (pani) with a vinyl binder and solvent, having good adhesion and sufficient thickness, for corrosion protection of steel surfaces in acid and saline environment. The paint system of the present invention is with conducting polyaniline as pigment in a vinyl binder which forms a thick corrosion resistant, adherent and stable passive layer over steel, whereas the hitherto known paint system has non conducting polyaniline and conducting polyaniline and conducting polyaniline in acrylic binder, resulting in a coating having poor adhesion and which does not provide protection in acid media. The non-obvious inventive step which enables realize the novelty resides in the conducting polyaniline pigment containing paint with vinyl binder. The process of the present invention involves the following steps: (1) Preparation of polyaniline pigment. (2) Preparation of paint system containing polyaniline with vinyl resin. The polyamline pigment was prepared using the following ingredients and parameters: Aniline: 0.8 to 1.2 M Hydrochloric acid : 0.8 to 1.2 M Ammonium persulphate : 0.8 to 1.2 M Water: 500 to 700 ml PH=1 Temperature 5 ±1°C The paint using polyaniline as pigment was prepared by using the synthesized polyaniline along with the following ingredients: Vinyl resin 400 to 450 gm Methyl isobutyl ketone 700 to 750 gm Polyaniline 32 to 45 gm The following examples are given by way of illustration of the working of the invention in actual practice and should not be construed to limit the scope of the present invention. Example-1 In this example, through total immersion studies, the corrosion resistance of polyaniline pigment coating on steel was tested by immersing coated samples in 3 % NaCI and 0.1 N HCI for a period of 30 days and visually inspected. Polyaniline pigment was prepared by dissolving 1M of distilled aniline in 500 ml of 1M HCI and pre-cooled to a temperature of 5° ± 1° C. 1M solution of ammonium persulphate, pre-cooled to a temperature of 5° ± 1° C, was added drop wise to the pre cooled aniline and acid mixture for about 1.5 hours with constant stirring. The reaction was conducted at a temperature of 5° + 1° C. After the addition, the stirring was continued for a further 2 hours for ensuring complete polymersation. A dark green coloured conducting polyaniline was filtered and repeatedly washed with distilled water to remove excess acid content. The polymer was air dried for few hours and oven dried at about 80° C for 2 hours. The dried polyaniline was fine grained using mortar and ready for making the paint. The paint containing polyaniline pigment was prepared by the following procedure: Vinyl resin of average molecular weight 30,000 comprising of vinyl acetate, and vinyl chloride was dissolved in methyl isobutyl ketone solvent in the following manner: 400 gms of vinyl resin was taken in attritor. To this, 720 gm of methyl isobutyl ketone (MIBK) was added. The mixture was stirred slowly for 24 hours for complete soubility. To this prepared vinyl solution, 36 gms of synthesized polyaniline was added. After the complete dispersion of pigment, 100gm of the MIBK solvent was added and the paint was transferred to a container. The coating was applied mild steel panels of size 7.5 cm X 5 cm X 0.2 cm and sand blasted to Sa2!£ . The coating thickness was in the range of 50 ± 5 urn per coat. After 2 hours of drying another coat was applied. The properties of the paint was as follows: Touch dry : 1.0 hours Complete dry ; 2.0 hours Volume solids : 30 to 33% Thickness / coat : 50 ± 5 j^m PVC : 9 to 10% The sand blasted mild steel panels of size 7.5 cm X 5 cm X 0.2 cm was coated with the prepared paint by brush and allowed to dry for a period of 72 hours. After drying, the coated samples were exposed to 3 % NaCI and 0.1 N HCI for a period of 30 days. At the end of the test period, the coated samples were visually inspected. The test results of the total immersion studies are given in Table-1 below: The absence of rust formation on the coated samples even after 30 days of immersion is indicative of corrosion resistance of the coating. Example-2 In this example, the corrosion resistance of the polyaniline pigment coating has been found out by measuring the potential of the coated metal immersed in 3 % NaCI and 0.1 N HCI. The coated steel samples were prepared as given in example-1. A glass tube of 1 cm diameter and 3 cm height was fixed on the coated steel sample using adhesive (m-seal). In the glass tube 3 % NaCI solution and 0.1 N HCI were poured and a saturated calomel electrode was placed inside the solution. The potential of the steel samples were measured by making electrical contact by scratching paint at one of the ends using digital multimeter. The results of potential measurements obtained are given in table -2 below: The noble potential values even after 30 days of immersion are indicative of the higher corrosion resistance of the coating. This higher corrosion resistance is due to the passivation of iron surface by forming a stable layer. Example-3 In this example, the corrosion resistance of polyaniline pigment coating has been found out by impedance behaviour of coated steel in 3 % NaCI and 0.1 N HCI. The coated mild steel sample as given in example-2, was tested for the impedance characteristics by using SI 1280 Electrochemistry System, Solatron, UK. The results obtained for impedance studies are given in Table-3 below: The above results show that the high values of impedance of coated samples even after 30 days of immersion indicate the high corrosion resistant nature of the coating. Example-4 In this example, the corrosion resistance of polyaniline pigmented coating has been found out by salt spray exposure studies. The coated samples as given in Example I has been exposed for salt spray test (ASTM B117) for a period of 720 hours (30 days). The specimens were visually examined for the rust product at the end of 30 days. The results of the salt spray studies are given in table-4 below: The main advantages of the present invention are: 1. A corrosion resistant non-toxic conducting polyaniline (pani) pigment containing paint for corrosion prevention of steel surfaces, which obviates the disadvantages of the hitherto known prior art. 2. The coating formed on steel using polyaniline containing paint is highly adherent. 3. The coating forms a thick corrosion resistant and stable passive layer over steel. 4. The coating for steel using the polyaniline containing paint is found to be highly corrosion resistant in acid and saline environment. 5. The toxic pigment used in conventional paint system is eliminated. 6. The paint containing non-toxic conducting polyaniline will be a substitute for the paint systems containing toxic pigments. We claim: 1. A corrosion resistant non-toxic paint containing conducting polyaniline (pani) for corrosion prevention of steel surfaces, which comprises non-toxic conducting polyaniline (pani) with a vinyl binder and solvent. 2. A corrosion resistant non-toxic paint containing conducting polyaniline (pani) as claimed in claim 1, wherein the vinyl binder is a vinyl resin of high molecular weight having average molecular weight of the order of 30,000. 3. A corrosion resistant non-toxic paint containing conducting polyaniline (pani) as claimed in claims 1-2, wherein the vinyl binder is a vinyl resin such as vinyl acetate, vinyl chloride or mixture thereof. 4. A corrosion resistant non-toxic paint containing conducting polyaniline (pani) as claimed in claims 1-3, wherein the solvent is methyl isobutyl ketone. 5. A process for preparing corrosion resistant non-toxic paint containing conducting polyaniline (pani) for corrosion prevention of steel surfaces, claimed in claim 1, which comprises: (i)preparing a conducting polyaniline (pani) by dissolving 0.8 to 1.2 M of distilled aniline in 0.8 to 1.2 M Hydrochloric acid, cooling the aniline and acid mixture to a temperature of 5° ± 1° C; adding pre-cooled 0.8 to 1.2 M ammonium persulphate solution drop wise to the said pre-cooled aniline and acid mixture for 1.5 hours under constant stirring, maintaining the reaction mixture at a temperature of 5° ± 1° C; continue the stirring for a further period of the order of 2 hours for ensuring complete polymersation; filtering to obtain a dark green coloured conducting polyaniline; washing repeatedly with distilled water to remove excess acid content; air drying for a few hours followed by oven drying at a temperature of 80° C for 2 hours; fine grinding the dried polyaniline; (ii)preparing a vinyl solution by adding solvent such as methyl isobutyl ketone (MIBK) to vinyl resin of high molecular weight having average molecular weight of the order of 30,000, such as vinyl acetate, vinyl chloride or mixture thereof, under constant slow stirring for a period of 24 hours for complete soubility; (iii)dispersing completely the dried polyaniline powder, obtained in step (i), in the said vinyl solution, obtained in step (ii), followed by adding MIBK solvent to obtain corrosion resistant paint. 6. A process as claimed in claim 5, wherein the molar concentrations of aniline, hydrochloric acid and ammonium persulphate are equal.

Full Text

The present invention relates to a corrosion resistant non-toxic paint containing conducting polyaniline (pani) for corrosion prevention of steel surfaces and process thereof
The present invention particularly relates to a corrosion resistant conducting polyaniline (PANI) containing paint for corrosion prevention of steel surfaces and a process for preparing the said paint. The present invention more particularly relates to a corrosion resistant conducting polyaniline (PANI) containing paint with vinyl binder for corrosion prevention of steel surfaces and a process for preparing the said paint.
The steel structures are coated by paint in order to prevent corrosion when exposed to atmosphere. Various primer coating systems based on paints containing pigments such as zinc phosphate, zinc chromate etc have been developed. Most of these coating systems contain toxic pigments and hence it is desirable to develop a coating system containing non-toxic pigment. In this regard, conducting polymer can be used as pigment by replacing the conventional toxic pigments used in paints. The new class of primers containing inherently conducting polymers, have got more tolerence to pin holes due to the passivating ability of pigments.
It is reported [G. Mengoli, M. Munari, P. Bianco and M. Musiani, J. Appl.
Polymer Sci., 26, 4247 (1982).] that polyaniline containing paints offer high
corrosion resistant coatings. Santos etal [J.R. Santos.Jr., L.H.C. Mattoso and A.J.
Motheo, Electrochimica Acta, 43, 309 (1998).] have studied the corrosion
resistant property of steel coated with polyaniline by spraying a 2 % solution of
polyaniline in N methyl pyrrolidine. They found that the steel coated with
polyamine gained nearly 100 mV in corrosion potential in 3 % NaCI and a low
corrosion rate was observed. This change in corrosion potential has been
attributed due to the formation of a passivated layer. Further, these studies
showed that the PAN I film loses water when kept out of the solution and returns to the original state after some time in contact with the solution without losing electrical and mechanical characteristics. This effect is probably due to the presence of air which keeps PAN I in the emaraldine oxidation state. Wessling etal [B. Wessling and J. Posdorfer, Electrochimica Acta, 44, 2139 (1999).] have studied the performance of polyaniline primer coatings on steel by salt spray test, electrochemical impedance spectroscopy and Scanning Kelvin-Probe in 3 % NaCI. They have found that the coating system with polyaniline primer has been found to be corrosion resistant. The polyaniline coating on steel is able to protect the scratches and pinholes present in the coating by the passivation of exposed areas [ W.K. Lu, R. L. Elsenbaumer and B. Wessiling, Synthetic Metals, 71, 2163 (1995) ]. However the coating is not of sufficient thickness in a single coat. The mechanistic investigation of polyaniline corrosion protection using scanning reference electrode technique has been made by Kinlen etal [P.J. Kinlen, V. Menon and Y. Ding, J. Electrochem. Soc., 146, 3690 (1999)]. They have found that polyaniline coatings passivate the pinhole defects in coatings. Further they have shown that phosphonic acid salts of polyaniline are more effective for corrosion protection than sulfonic acid salts. A model has been proposed for the protection of polyaniline coatings. In all the above studies it has been shown that the conducting polymer coating such as polyaniline stabilizes the potential of the metal in a passive region and maintain a protective oxide layer on the metal. Both SEM and XPS studies have revealed that an oxide layer has been formed between the PANI coating and the steel surface and is composed mainly of FeaOa above a very thin FesO4 layer [B. Wessling, Adv. Mater, 6, 226 (1994); A. Talo, P. Passiniemi, O. Forsen, S. Ylassari, Synth. Met, 85, 1333 (1997); B. Wessling, Synth. Met, 85, 1313 (1997)]. It has been reported by Wrobleski etal [D.A. Wrobleski, B.C. Benicewicz,
K.G.Thompson and C.J. Bryan, Poly. Chem., 35, 265 (1994)] that the doped electrically conducting form of polyaniline film (film of thickness 0.005 cm) on steel with epoxy top coat gave excellent performance in 3.5 % NaCI and 0.1 M HCI even at scribed areas. However this coating is not adherent to the surface. The mechanism of protection of conducting polymer coating has been investigated by Jain etal [F.C. Jain, J.J. Rosato, K.S. Kalonia and V.S. Agarwala, Corrosion, 42, 700 (1986)]. It has been stated that the doped conducting polymer will generate an electric field that will restrict the flow of electrons from the metal to an outside oxidizing species thus preventing the corrosion. The corrosion resistance of PANI coatings on steel is also reported T.P.Me Andrew, A.G. Gilicinski and L.M.Robson, US Patent 5441772 (1995)]. However the studies on the anticorrosive properties of un doped polyaniline coated on mild steel have shown that the performance of PANI coated system is not good due to the poor adhesion [W.S. Araujo, I.C.P. Margarit, M. Ferreira, O.R. Mattos, P.Lima Neto, Electrochimica Acta, 46, 1307 (2001)]. In the review [T. P. Me Andrew, TRIP, 5, 7 (1997)] by Mcandrew has stated that the future for the use of electrically conducting polymers in corrosion resistant coatings appears promising, especially as additives to improve the performance of existing coating system. In a recent study [A. B. Samli, A. S. Pantekar, J. Rengarajan and P.C. Deb., Prog. Org. Coatings, 47, 1 (2003)], it is reported that the lower polyaniline loaded paint has been found to be more corrosion resistant. The use of such coatings in acid media is not estabilished.
Hitherto it is reported in various patents the use of polyaniline in corrosion resistant coatings.
Reference may be made to US patent No. 5,853,621 (Dt 29 Dec1998 by Miller etal) on "Corrosion resistant paint", which deals with the paint system containing non conducting conjugate polymers.
Reference may be made to another US patent 6,054,514 (Dt25 Apr 2000 by Kulkarni etal) on "Additives for enhancing corrosion protection of metals", which deals with coating system containing polyaniline in acrylic binder resistant to neutral media.
Reference may also be made to US patent 5,928,795 (Dt 27 July 1999 by Spellane etal), wherein is disclosed protective coatings with polyaniline to protect aluminium substrates.
Reference may also be drawn to D.A. Wrobleski, B.C. Benicewicz, K.G.Thompson and C.J. Bryan, Poly. Chem., 35, 265 (1994); W.K. Lu, R. L. Elsenbaumer and B. Wessiling, Synthetic Metals, 71, 2163 (1995); A. B. Samli, A. S. Pantekar, J. Rengarajan and P.C. Deb., Prog. Org. Coatings, 47 ,1 (2003), and US Patent nos.: 5,853, 621 and 6, 054, 514.
Hitherto it is reported that steel samples coated with polyaniline containing paint has been found to offer corrosion protection. The drawbacks of the coating reported are:
(i) coatings have poor adhesioin;
(ii) sufficient thickness can not be obtained in a single coat; (iii) corrosion protection in acid media is not established; (iv) the paints were formulated using PANI pigment and solvent without any binder; and
(v) the paints were formulated with non conducting polyaniline pigment and conducting polyaniline pigment in acrylic binder for protection of steel in neutral media.
The main objective of the present invention is to provide a corrosion resistant polyaniline (pani) containing paint for corrosion prevention of steel surfaces, which obviates the disadvantages of the hitherto known prior art.
Another objective of the present invention is to provide a corrosion resistant non toxic conducting polyaniline (PANI) containing paint for corrosion prevention of steel surfaces.
Still another objective of the present invention is to provide a corrosion resistant conducting polyaniline (PANI) containing paint with a vinyl binder for corrosion prevention of steel surfaces.
Yet another objective of the present invention is to provide a process for preparing a corrosion resistant conducting polyaniline (pani) containing paint with vinyl binder for corrosion prevention of steel surfaces, which obviates the disadvantages of the hitherto known prior art.
A further objective of the present invention is to provide a non toxic paint system containing conducting polyaniline with a vinyl binder, having good adhesion and sufficient thickness, for corrosion protection of steel surfaces in acid and saline environment and a process for preparing the said paint.
In the present invention there is provided a corrosion resistant non toxic paint containing conducting polyaniline (pani) with a vinyl binder and solvent, having
good adhesion and sufficient thickness, for corrosion protection of steel surfaces in acid and saline environment and a process for preparing the said paint.
Accordingly, the present invention provides a corrosion resistant non-toxic paint
containing conducting polyaniline (pani) for corrosion prevention of steel surfaces,
which comprises non-toxic conducting polyaniline (pani) with a vinyl binder and
solvent
In an embodiment of the present invention, the vinyl binder is a vinyl resin of high
molecular weight having average molecular weight of the order of 30,000.
In another embodiment of the present invention, the vinyl binder is a vinyl resin such as vinyl acetate, vinyl chloride or mixture thereof.
In still another embodiment of the present invention, the solvent is such as methyl isobutyl ketone.
Accordingly, the present invention provides a process for preparing the above said corrosion resistant non toxic paint, which comprises:
(i) preparing a conducting polyaniline (pani) by dissolving 0.8 to 1.2 M of distilled aniline in 0.8 to 1.2 M Hydrochloric acid, cooling the aniline and acid mixture to a temperature of 5° ± 1° C; adding pre-cooled 0.8 to 1.2 M ammonium persulphate solution drop wise to the said pre-cooled aniline and acid mixture for 1.5 hours under constant stirring, maintaining the reaction mixture at a temperature of 5° ± 1° C; continue the stirring for a further period of the order of 2 hours for ensuring complete polymersation; filtering to obtain a dark green coloured conducting

polyaniline; washing repeatedly with distilled water to remove excess acid content; air drying for a few hours followed by oven drying at a temperature of 80° C for 2 hours; fine grinding the dried polyaniline;
(ii) preparing a vinyl solution by adding solvent such as methyl isobutyl ketone (MIBK) to vinyl resin of high molecular weight having average molecular weight of the order of 30,000, such as vinyl acetate, vinyl chloride or mixture thereof, under constant slow stirring for a period of 24 hours for complete soubility;
(iii) dispersing completely the dried polyaniline powder, obtained in step (i), in the said vinyl solution, obtained in step (ii), followed by adding MIBK solvent to obtain corrosion resistant paint.
In an embodiment of the present invention, the molar concentrations of aniline, acid and ammonium persulphate are equal.
The novelty of the present invention resides in providing a corrosion resistant non toxic paint containing conducting polyaniline (pani) with a vinyl binder and solvent, having good adhesion and sufficient thickness, for corrosion protection of steel surfaces in acid and saline environment. The paint system of the present invention is with conducting polyaniline as pigment in a vinyl binder which forms a thick corrosion resistant, adherent and stable passive layer over steel, whereas the hitherto known paint system has non conducting polyaniline and conducting
polyaniline and conducting polyaniline in acrylic binder, resulting in a coating having poor adhesion and which does not provide protection in acid media.
The non-obvious inventive step which enables realize the novelty resides in the conducting polyaniline pigment containing paint with vinyl binder.
The process of the present invention involves the following steps:
(1) Preparation of polyaniline pigment.
(2) Preparation of paint system containing polyaniline with vinyl resin.
The polyamline pigment was prepared using the following ingredients and parameters:
Aniline: 0.8 to 1.2 M Hydrochloric acid : 0.8 to 1.2 M Ammonium persulphate : 0.8 to 1.2 M Water: 500 to 700 ml PH=1 Temperature 5 ±1°C
The paint using polyaniline as pigment was prepared by using the synthesized polyaniline along with the following ingredients:
Vinyl resin 400 to 450 gm
Methyl isobutyl ketone 700 to 750 gm
Polyaniline 32 to 45 gm
The following examples are given by way of illustration of the working of the invention in actual practice and should not be construed to limit the scope of the present invention.
Example-1
In this example, through total immersion studies, the corrosion resistance of polyaniline pigment coating on steel was tested by immersing coated samples in 3 % NaCI and 0.1 N HCI for a period of 30 days and visually inspected. Polyaniline pigment was prepared by dissolving 1M of distilled aniline in 500 ml of 1M HCI and pre-cooled to a temperature of 5° ± 1° C. 1M solution of ammonium persulphate, pre-cooled to a temperature of 5° ± 1° C, was added drop wise to the pre cooled aniline and acid mixture for about 1.5 hours with constant stirring. The reaction was conducted at a temperature of 5° + 1° C. After the addition, the stirring was continued for a further 2 hours for ensuring complete polymersation. A dark green coloured conducting polyaniline was filtered and repeatedly washed with distilled water to remove excess acid content. The polymer was air dried for few hours and oven dried at about 80° C for 2 hours. The dried polyaniline was fine grained using mortar and ready for making the paint.
The paint containing polyaniline pigment was prepared by the following procedure:
Vinyl resin of average molecular weight 30,000 comprising of vinyl acetate, and vinyl chloride was dissolved in methyl isobutyl ketone solvent in the following manner:
400 gms of vinyl resin was taken in attritor. To this, 720 gm of methyl isobutyl ketone (MIBK) was added. The mixture was stirred slowly for 24 hours for complete soubility. To this prepared vinyl solution, 36 gms of synthesized
polyaniline was added. After the complete dispersion of pigment, 100gm of the MIBK solvent was added and the paint was transferred to a container. The coating was applied mild steel panels of size 7.5 cm X 5 cm X 0.2 cm and sand blasted to Sa2!£ . The coating thickness was in the range of 50 ± 5 urn per coat. After 2 hours of drying another coat was applied.
The properties of the paint was as follows:
Touch dry : 1.0 hours
Complete dry ; 2.0 hours
Volume solids : 30 to 33%
Thickness / coat : 50 ± 5 j^m
PVC : 9 to 10%
The sand blasted mild steel panels of size 7.5 cm X 5 cm X 0.2 cm was coated with the prepared paint by brush and allowed to dry for a period of 72 hours. After drying, the coated samples were exposed to 3 % NaCI and 0.1 N HCI for a period of 30 days. At the end of the test period, the coated samples were visually inspected. The test results of the total immersion studies are given in Table-1 below:

The absence of rust formation on the coated samples even after 30 days of immersion is indicative of corrosion resistance of the coating.
Example-2
In this example, the corrosion resistance of the polyaniline pigment coating has been found out by measuring the potential of the coated metal immersed in 3 % NaCI and 0.1 N HCI. The coated steel samples were prepared as given in example-1. A glass tube of 1 cm diameter and 3 cm height was fixed on the coated steel sample using adhesive (m-seal). In the glass tube 3 % NaCI solution and 0.1 N HCI were poured and a saturated calomel electrode was placed inside the solution. The potential of the steel samples were measured by making electrical contact by scratching paint at one of the ends using digital multimeter. The results of potential measurements obtained are given in table -2 below:

The noble potential values even after 30 days of immersion are indicative of the higher corrosion resistance of the coating. This higher corrosion resistance is due to the passivation of iron surface by forming a stable layer.
Example-3
In this example, the corrosion resistance of polyaniline pigment coating has been found out by impedance behaviour of coated steel in 3 % NaCI and 0.1 N HCI. The coated mild steel sample as given in example-2, was tested for the impedance characteristics by using SI 1280 Electrochemistry System, Solatron, UK. The results obtained for impedance studies are given in Table-3 below:

The above results show that the high values of impedance of coated samples even after 30 days of immersion indicate the high corrosion resistant nature of the coating.
Example-4
In this example, the corrosion resistance of polyaniline pigmented coating has been found out by salt spray exposure studies. The coated samples as given in Example I has been exposed for salt spray test (ASTM B117) for a period of 720 hours (30 days). The specimens were visually examined for the rust
product at the end of 30 days. The results of the salt spray studies are given in table-4 below:

The main advantages of the present invention are:
1. A corrosion resistant non-toxic conducting polyaniline (pani) pigment
containing paint for corrosion prevention of steel surfaces, which
obviates the disadvantages of the hitherto known prior art.
2. The coating formed on steel using polyaniline containing paint is
highly adherent.
3. The coating forms a thick corrosion resistant and stable passive
layer over steel.
4. The coating for steel using the polyaniline containing paint is found
to be highly corrosion resistant in acid and saline environment.
5. The toxic pigment used in conventional paint system is eliminated.
6. The paint containing non-toxic conducting polyaniline will be a
substitute for the paint systems containing toxic pigments.

We claim:
1. A corrosion resistant non-toxic paint containing conducting polyaniline (pani) for corrosion prevention of steel surfaces, which comprises non-toxic conducting polyaniline (pani) with a vinyl binder and solvent.
2. A corrosion resistant non-toxic paint containing conducting polyaniline (pani) as claimed in claim 1, wherein the vinyl binder is a vinyl resin of high molecular weight having average molecular weight of the order of 30,000.
3. A corrosion resistant non-toxic paint containing conducting polyaniline (pani) as claimed in claims 1-2, wherein the vinyl binder is a vinyl resin such as vinyl acetate, vinyl chloride or mixture thereof.
4. A corrosion resistant non-toxic paint containing conducting polyaniline (pani) as claimed in claims 1-3, wherein the solvent is methyl isobutyl ketone.
5. A process for preparing corrosion resistant non-toxic paint containing conducting polyaniline (pani) for corrosion prevention of steel surfaces, claimed in claim 1, which comprises:
(i)preparing a conducting polyaniline (pani) by dissolving 0.8 to 1.2 M of distilled aniline in 0.8 to 1.2 M Hydrochloric acid, cooling the aniline and acid mixture to a temperature of 5° ± 1° C; adding pre-cooled 0.8 to 1.2 M ammonium persulphate solution drop wise to the said pre-cooled aniline and acid mixture for 1.5 hours under constant stirring, maintaining the reaction mixture at a temperature of 5° ± 1° C; continue the stirring for a further period of the order of 2 hours for ensuring complete polymersation; filtering to obtain a dark green coloured conducting polyaniline; washing repeatedly with distilled water to remove excess acid content;

air drying for a few hours followed by oven drying at a temperature of 80° C for 2 hours; fine grinding the dried polyaniline;
(ii)preparing a vinyl solution by adding solvent such as methyl isobutyl ketone (MIBK) to vinyl resin of high molecular weight having average molecular weight of the order of 30,000, such as vinyl acetate, vinyl chloride or mixture thereof, under constant slow stirring for a period of 24 hours for complete soubility; (iii)dispersing completely the dried polyaniline powder, obtained in step (i), in the said vinyl solution, obtained in step (ii), followed by adding MIBK solvent to obtain corrosion resistant paint.
6. A process as claimed in claim 5, wherein the molar concentrations of aniline, hydrochloric acid and ammonium persulphate are equal.

Documents:

« Previous Patent

Next Patent »

Patent Number

254215

Indian Patent Application Number

639/DEL/2006

PG Journal Number

40/2012

Publication Date

05-Oct-2012

Grant Date

03-Oct-2012

Date of Filing

10-Mar-2006

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN, RAFI MARG, NEW DELHI-110 001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	DINESH CHANDRA TRIVEDI	SCIENTIST CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE KARAIKUDI - 630 006
2	SADAGOPAN SATHIYANARAYANAN	SCIENTIST CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE KARAIKUDI - 630 006
3	SUNDARARAJAN MUTHUKRISHNAN	SCIENTIST CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE KARAIKUDI - 630 006
4	GOPALACHARI VENKATACHARI	SCIENTIST CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE KARAIKUDI - 630 006

PCT International Classification Number

C09D 5/08

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA