Title of Invention

A NOVEL PROCESS FOR THE DEVELOPMENT OF CORROSION RESISTANCE THIN ORGANIC COATING FOR ZINC-COATED STEEL .

Abstract

A novel process for the development of corrosion resistance thin organic coating for zinc coated steel, comprising the steps of: - formulating a water soluble emulsion comprising a water based styrenated acrylic copolymer emulsion, polyurethane resin and rust preventive additives for use as white rust corrosion resistant coating by carrying out polymerizing reaction of acrylic monomers and redox initiators at a temperature 75°C-85°C for a period of 3 to 4 hours; - cooling the formulation; - adjusting the pH value of said styrenated acrylic copolymer to the range of 7 to 9; and - applying the formulation on zinc and zinc alloy coated steel in a thin layer.

Full Text

FIELD OF APPLICATION The present invention relates to a process for providing an enhanced corrosion resistant thin organic coating (TOC) for zinc coated steel and rust resistant zinc coated steel with a thin organic coating. BACKGROUND OF THE INVENTION The out of the bath surface of zinc and zinc alloy coatings are highly susceptible to corrosion. Corrosion products formed on zinc coating are generally referred to as 'white rust'. Inorganic chromate passivation is usually applied directly after galvanizing in line to enhance the corrosion protection properties of zinc and zinc alloy. This technique is widely applied as an economical method of corrosion prevention. In recent past a new technology was developed in the post treatment of galvanized sheets known as "thin organic coating" (TOC) or "organic composite coating". This coating formulation contains both organic and inorganic compounds in the formulation. United States Patent No. 3,036,934 describes the organic coating formulation comprising water emulsion acrylic polymer and the soluble chromium which enhances the white rust resistance of the zinc and zinc alloy sheet substrate. The formulations enhance white rust resistance of the coating comparatively better than inorganic chromate passivation. However, it does not give lubricity properties. Furthermore, a desirable higher corrosion resistance is also not achievable by this formulation. Other US Patent Numbers 5,482,787 and 5,294,485 describe the organic coating formulation having improved corrosion resistance and weldability. These formulations describe the two steps coating application. The first step is coating of inorganic chromate layer followed by organic coating layer. The organic polymer layer is based on an epoxy resin and is baked at a higher temperature of 100-200° C. There is therefore, a need for a thin organic coating (TOC) formulation which will not only enhance the white rust resistance of the zinc and zinc alloy substrate but also provide anti-fingerprint resistance properties, superior lubricity and paint adhesion. SUMMARY OF THE INVENTION The main object of the present invention is to provide a zinc and zinc alloy substrate with enhanced white rust resistance properties. Another object of the present invention is to provide a zinc and zinc alloy substrate with anti-fingerprint resistance and increased lubricity and weldability. These and other objects are achieved by using a combination of organic resins and soluble chromium compound which provide corrosion protection to the zinc coated steel and steel sheets. This protection mechanism is by the barrier effect of the organic resin and the self healing effect of the hexavalent chromium. The best physical barrier effect of organic resin layer can be made by using water soluble styrene acrylic resin and polyurethane together. Another object of the present invention is to provide a zinc and zinc alloy substrate with anti-fingerprint resistance and increased lubricity and weldability. Ammonium dichromate is used as a chromium compound. It is important that the amount of total chromium on each side of the thin organic coated surface be held between 10 to about 30 mg/m2 for colourless chromate coating. Below 10 mg/m2, only partial protection against white rusting can be obtained, while above 30mg/mg light yellow colour appears. It has been observed that 20 mg/m2 gives good corrosion protection with a resin coating weight of approximately 1000 mg/m2. Colloidal silica when added further enhances the corrosion resistance of the coating layer. Wax can be added to improve the lubrication property of the coating. Total dry coating weight can be in the range of 500 - 3000 mg / m2. Thus the present invention provides a process for providing an enhanced corrosion resistant thin organic coating for zinc coated steel, like zinc coated steel sheet, comprising the steps of: formulating a water soluble emulsion comprising a water based styrenated acrylic copolymer emulsion, polyurethane resin and rust preventive additives for use as white rust corrosion resistant coating by carrying out polymerizing reaction of acrylic monomers and redox initiators at a temperature of 75° C - 85º C for a period of 3 to 4 hours; cooling the formulation; adjusting the pH value of said styrenated acrylic copolymer to the range of 7 to 9; and applying the formulation on zinc and zinc alloy coated steel in a thin layer. The present invention enhances the white rust resistance of the galvanized steel sheet by the application of organic coating applied as post treatment. The organic coating formulation gives a thin, transparent colourless passivation coating on the sheet surface thereby maintaining the bright appearance of zinc surface. In addition to corrosion resistance, this organic coating also gives anti- fingerprint resistance, lubricity and weldability of the coated sheet. The basic coating composition comprises of water-soluble styrene acrylic polymer, polyurethane emulsion and soluble chromium. Colloidal silica and polyethylene wax can be added for further enhancing the corrosion resistance an improving the lubrication property of the coating. DETAILED DESCRIPTION The thin organic coating of the present invention provides an excellent corrosion resistance, paint adhesion, lubrication, anti-fingerprints properties and allows a practical level of grounding and weldability. The coating increases the life of sheet by the barrier effect of the organic layer. In addition, the rust preventive additives such as the soluble chromate and colloidal silica are added to the organic film which further improves the corrosion resistance of the coated steel sheet by the self healing effect of the chromium present in the formulation. The lubricant added to the organic film improves the lubricative property of the coated steel sheet during press-forming of the sheet. The thin layer of organic coating can be applied in the continuous galvanizing line in place of chromate coating or can be applied over the chromate coating. The detailed description of the coating formulation is given below. The organic film comprises styrene acrylic copolymer, polyurethane polymer and soluble chromium. Colloidal silica and polyethylene wax can be advantageously added. The monomers are selected from styrene, methyl methacrylate, methacrylic acid, acrylic acid, itaconic acid, butyl acrylate, ethyl hexyl acrylate and ethyl acrylate. The redox initiators are selected from potassium persulphate, ammonium persulphate and hydrogen peroxide. The rate of addition of monomers to the reactor is in the range of 45 minutes to one hour per 200 grams of the monomer mixture. The rate of addition of initiator and emulsifier mixture to the reactor is in the range of 45 minutes to one hour per 200 grams of the initiator emulsifier mixture. 50 to 60 parts of styrene acrylic copolymer is mixed with the polyurethane resin emulsion of 25 to 35 parts. 5 to 10 parts of the chromate solution are added to the formulation. Colloidal silica of 4 to 8 parts are added to the formulation for further enhancing the corrosion resistance of the coating layer. 4 to 8 parts of polyethylene wax are added to the formulation to improve the lubrication property of the coating layer. The thin organic coating formulation as described in the present invention can be applied by dip coating, spray coating, roller coating on hot dip zinc and zinc alloy coated sheets. Water soluble styrenated acrylic copolymer emulsion for use as corrosion resistant thin organic coating on zinc coated steel sheets in the present invention has been developed carrying out polymerization reaction of acrylic monomers and redox initiators at a temperature range of 75 to 85° C for a period ranging from 3 to 4 hours, cooling the temperature and adjusting the pH value of the styrenated acrylic copolymer to the range of 7 to 9. The organic resins used in this formulation are water based styrene acrylic copolymers and polyurethane. The water based styrene acrylic copolymer formulation contains 38% of solid content. In the laboratory, the styrene acrylic copolymer (Example 1 formulation) is adjusted in such a way that the formed copolymer gives 38% of solid content at the end of the reaction. Also, it is found that the styrene acrylic copolymer (Example 2 formulation) 45% of solid content and (Example 3 formulation) 50% of solid content give similar performance to Example 1 formulation. However, these two have to be dissolved in deionized water to make 38% of solid content and then used in the coating formulation. It has also been observed in the present invention that some of the commercially available styrene acrylic copolymer with the following properties: stabilization emulsifier, styrene acrylic monomers, approximately 50%, solid content, Brookfield viscosity 20 - 70 at 30°C Ps, pH 7.5 - 9, specific gravity approximately 1.05 at 30°C, MFFT 15 - 18°C, may also be used as a part of the formulation to provide adequate coating performance. The water based Polyurethane resin used in this formulation contains approximately 25% solid content. The polyurethane resin used in this invention is of pH 6.5 to 7.5. It is a very soft dispersion of fine particle size. The colloidal silica used in this formulation contains 15 to 30% solid content. The average particle size is 4-15 mm and the pH of the solution is 9.5 - 10. Its density is 1.1. to 1.25 g/cm3. The polyethylene wax emulsion used in this formulation is a - white translucent emulsion having 34 - 36 % solid content, pH 8.0 - 10.5 with typical particle size of 0.6 microns. The Drop point of the wax component is 138°C and hardness of wax is 0.5 maximum dmm. The thin organic coating formulation after applying on the sheet surface gives a dry coating weight of 500 - 3000 mg/m2. The thin organic formulation after applying on sheet surface gives a total chromium weight of 10-30 mg/m2 per side. The preparation of acrylic resin and the formulation of thin organic coating consisted of acrylic resin, polyurethane resin, chromium compound, colloidal silica and the wax used in the present investigation are described below as examples. EXAMPLE 1 (a) Formulation of styrene acrylic copolymer The acrylic resin polymer used in this invention has been made by the following methods. A 2 Kg reactor with flange containing 5 inlets for nitrogen gas, thermometer, water condenser, stirrer and additional inlets for the catalyst-emulsifier mixture and the monomer mixture was used for the polymerization of water based acrylic copolymer emulsion. Sodium metabisulphite (0.4 to 0.8 g) dissolved in 30 ml of deionized water (DIW) is charged into the reactor and the temperature of the solution maintained at 75° C before the addition of the monomers and catalyst emulsifier mixture into the reactor. Before adding sodium metabisulphite solution into the reactor, 170 ml of DIW is added into the reactor. The monomer mixture containing Styrene (110 to 150g), Butyl acrylate (110 to 150g), methyl methacrylate (110 to 150g) and methacrylic acid (5 to lOg) was transferred into one of the additional columns. A mixture of sodium lauryl sulphate (5 to 20g), alkylaryl polyether (HYOXYD 400) (4 to 10g) dissolved in 200 ml of deionized water and potassium persulphate (1 to 4 g) dissolved in 200 ml of Deionized water was transferred in another additional column and added to the reaction vessel at 120 rpm. The addition of the monomer mixture and catalyst emulsifier mixture was added slowly by dropwise method for 2 hours into the reactor under nitrogen atmosphere at 75° C. The reaction was allowed to proceed for 2 more hours. Afterwards the reaction temperature of the kettle was raised to 85°C and for 30 minutes to react completely or remove the excess monomer. The temperature of the reaction kettle was brought down to room temperature by circulation of cold water and the emulsion thus formed was filtered. The pH of the acrylic emulsion was adjusted to 7 to 9 by the addition of sodium hydroxide (40%), ammonia or triethanolamine. The solid content of the resin formulation was 38% and the pH was 7-9. (b) The chromate solution formulation: The ammonium dichromate chromate compound was used in this formulation as a soluble chromium. It was dissolved in deionized water at a concentration of 150 - 170 gm/l and the pH was around 2.5 to 4.5. Since the resin formulation was alkaline in nature, the chromate solution was made alkaline by the addition of sodium hydroxide to a pH value of 7.5 - 8.5. (c) The polyurethane resin: The water based Polyurethane resin used in this formulation contains approximately 25 % solid content. The polyurethane resin used in this invention is of pH 6.5 to 8. It is a very soft disperson of fine particle size. (d) The colloidal Silica: The colloidal silica used in this formulation contains 15 to 30% solid content. The average particle size is 4 -15 mm and the pH of the solution is 9.5-10. Its density is 1.1 to 1.25 g/cm3. (e) The polyethylene wax The polyethylene wax emulsion used in this formulation is a - white translucent emulsion having 34 - 36 % solid content, pH 8.0 - 10.5 with typical particle size of 0.6 microns. The Drop point of the wax component is 138°C and hardness of wax dmm is 0.5 max. The organic resin film comprising of (a) 50 to 60 parts by volume of styrene acrylic copolymer having solid content of 38%. This styrene acrylic Example 1 formulation was developed at the laboratory the method of formulation is given under the headline "Formulation of styrene acrylic copolymer" (b) 25 to 35 parts of by volume of chromate solution (c) 5 to 10 parts by volume of chromate solution. (d) 4 to 8 parts by volume of colloidal silica. (e) 4-8 parts by volume of polyethylese wax emulsion. The high-speed stirrer was used for the mixing of the organic coating constituents. The addition of the constituents was in the same order given above and stirring was done for 3 hours continuously. Example 2 (a) Formulation of styrene acrylic copolymer The acrylic resin polymer used in this invention has been made by following methods. A 2 Kg reactor with flange containing 5 inlets for nitrogen gas, thermometer, water condenser, stirrer and additional inlets for the catalyst emulsifier mixture and the monomer mixture was used for the polymerization of water based acrylic copolymer emulsion. Sodium metabisulphite (0.4 to 0.8 g) dissolved in 30 ml of deionized water (DIW) was charged into the reactor and the temperature of the solution was maintained at 75°C before the addition of the monomers and catalyst emulsifier mixture into the reactor. Before adding Sodium metabisulphite solution into the reactor, 170 ml of DIW is added into the reactor. The monomer mixture containing styrene (110 to 150g), ethyl acrylate (110 to 150g), methyl methacrylate (110 to 150g) and acrylic acid (5 to 10g) was transferred into one of the additional columns. A mixture of sodium lauryl sulphate (5 to 20g), alkylaryl polyether (HYOXYD 400) (4 to 10g) dissolved in 200 ml of deionized water and ammonium persulphate (1 to 4 g) dissolved in 200 ml of deionized water was transferred into another additional column and added to the reaction vessel at 120 rpm. The addition of the monomer mixture and catalyst emulsifier mixture was added slowly into the reactor under nitrogen atmosphere at 75°C by drop wise method for 2 hours. The reaction was allowed to proceed for 2 more hours. Afterwards the temperature of the reaction kettle was raised to 85°C and maintained at the same temperature for 30 minutes to react completely or remove the excess monomer. The temperature of the reaction kettle was brought to room temperature by circulation of cold water and the emulsion thus formed was filtered. The pH of the acrylic emulsion was adjusted to 7 to 9 by the addition of sodium hydroxide (40%) or ammonia or triethanolamine. The solid content of the resin formulation wps 45% and the pH was 7-9. (b) The chromate solution formulation: The ammonium dichromate was used in this formulation as a soluble chromium. It was dissolved in deionized water at a concentration of 150-170 gm/l and the pH was around 2.5 to 4.5. Since the resin formulation was alkaline and the chromate solution was made alkaline by adding sodium hydroxide and adjusting the pH to 7.5 - 8.5. (c) The polyurethane resin: The water based Poiyurethane resin used in this formulation contains approximately 25 % solid content. The poiyurethane resin used in this invention is of pH 6.5 to 8. It is a very soft dispersion of fine particle size. (d) The colloidal Silica: The colloidal silica used in this formulation contains 15 to 30% solid content. The average particle size is 4 - 15 nm and the pH of the solution is 9.5-10. Its density is 1.1 to 1.25 g/cm3. (e) The polyethylene wax The polyethylene wax emulsion used in this formulation is a - white translucent emulsion having 34 - 36 % solid content, pH 8.0 -10.5 with typical particle size of 0.6 microns. The Drop point of the wax component is 138° C and hardness of wax dmm is 0.5 maximum. The organic resin film comprised of: (a) 50 to 60 parts by volume of styrene acrylic copolymer having solid content of 38%. This styrene acrylic copolymer prepared from Example 2 formulation was developed at the laboratory with 45 solid content. This resin was dissolved in deionized water to make 38% of solid content. (b) 25 to 35 parts of by volume of polyurethane resin (c) 5 to 10 parts by volume of chromate solution. (d) 4 to 8 parts by volume of colloidal silica (e) 4 to 8 parts by volume of polyethylene wax. The high-speed stirrer was used for the mixing of the organic coating constituents. The addition of the constituents was in the order given above and stirring was done for 3 hours continuously. Example 3 (a) Formulation of styrene acrylic copolymer The acrylic resin polymer used in this invention has been made by following methods. A 2 Kg reactor with flange containing 5 inlets for nitrogen gas, thermometer, water condenser, stirrer and additional inlets for the catalyst emulsifier mixture and the monomer mixture was used for the polymerization of water based acrylic copolymer emulsion. Sodium metabisulphite (0.4 to 0.8 g) dissolved in 30 ml of deionized water (DIW) was charged into the reactor and the temperature of the solution was maintained at 75° C before the addition of the monomers and catalyst emulsifier mixture into the reactor. Before adding sodium metabisulphite solution into the reactor, 170 ml of DIW is added into the reactor. The monomer mixture containing styrene (110 to 150g), ethyl hexyl acrylate (110 to 150g), methyl methacrylate (110 to 150g) and itaconic acid (5 to 10g) was transferred into one of the additional columns. A mixture of sodium lauryl sulphate (5 to 20g), alkylaryl polyether (HYOXYD 400) (4 to 10g) dissolved in 200 ml of deionized water and potassium persulphate (1 to 4 g) dissolved in 200 ml of deionized water was transferred into another additional column and added to the contents of the reaction vessel at 120 rpm. The addition of the monomer mixture and catalyst emulsifier mixture was added slowly into the reactor under nitrogen atmosphere at 75° C by drop wise method for 2 hours. The reaction was allowed to proceed for 2 more hours. Afterwards the reaction of the kettle was raised to 85° C and maintained at that temperature for 30 minutes to react completely or remove the excess monomer. The temperature of the reaction kettle was brought down to room temperature by the circulation of cold water and the emulsion thus was filtered. The pH of the acrylic emulsion was adjusted to 7 to 9 by the addition of sodium hydroxide (40%) or ammonia or triethanolamine. The solid content of the resin formulation was 50% and the pH was 7-9. (b) The chromate solution formulation: The ammonium dichromate chromate compound was used in this formulation as a soluble chromium. It was dissolved in deionized water at a concentration of 150-170 gm/l and measured the pH which was around 2.5 to 4.5. Since the resin formulation is alkaline in nature and the chromate solution was made alkaline by adding sodium hydroxide and adjusting the pH to 7.5 - 8.5. (c) The polyurethane resin: The water based Polurethane resin used in this formulation contains approximately 25% solid content. The polyurethane resin used in this invention is of pH 6.5 to 8. It is a very soft dispersion of fine particle size. (d) The colloidal Silica: The colloidal silica used in this formulation contains 15 to 30% solid content. The average particle size is 4 - 15 nm and the pH of the solution is 9.5 - 10. Its density is 1.1 to 1.25 g/cm3. (e) The polyethylene wax The polyethylene wax emulsion used in this formulation is a - white translucent emulsion having 34 - 36% solid content, pH 8.0 - 10.5 with typical particle size of 0.6 microns. The Drop point of the wax component is 138° C and hardness of wax dmm is 0.5 maximum. The organic resin film comprised of: (a) 50 to 60 parts by volume of styrene - acrylic copolymer having a solid content of 38%. This styrene acrylic copolymer prepared from Example 3 formulation was developed at the laboratory with 50% of solid content. This resin was dissolved in deionized water to make 38% of solid content. (b) 25 to 35 parts by volume of polyurethane resin. (c) 5 to 10 parts by volume of chromate solution. (d) 4 to 8 parts by volume of colloidal silica. (e) 4-8 parts by volume of polyethylene wax. The high-speed stirrer was used for mixing all organic coating constituents. The addition of the constituents was in the order given above and stirring was done for 3 hours continuously. Example 4 (a) Styrene acrylic resin: The styrene acryline copolymer used in this formulation is a commercial manufactured resin product having following properties. The stabilization is emulsifier which consists of approximately 50% solid content and pH of 7.5 - 9 was used in this formulation. However, this commercially available polymer to be dissolved in deionized water to make 30% of solid content and then used in the coating formulation. The commercial available product used in the study having following properties: stabilization ernulsifier,styrene-acrylic monomers, approximately 50%, solid content, Brookfield viscosity 20-70 at 30°C Ps, pH 7.5 - 9, specific gravity approximately 1.05 at 30°C, MFFT15 - 18° C, particle size 0.05 - 0.005. (b) The chromate solution formulation: The ammonium dischromate chromate compound was used in this formulation as a soluble chromium. It was dissolved in deionized water at a concentration of 150 - 170 gm/l and measured the pH which was around 2.5 to 4.5. Since the resin formulation is alkaline in nature and the chromate solution was made alkaline by adding sodium hydroxide and adjusting the pH to 7.5 - 8.5. (c) The polyurethane resin: The water based Polyurethane resin used in this formulation contains approximately 25% solid content. The polyurethane resin used in this invention is of pH 6.5 to 8. It is a very soft dispersion of fine particle size. (d) The colloidal Silica: The colloidal silica used in this formulation contains 15 to 30% solid content. The average particle size is 4 - 15 nm and the pH of the solution is 9.5 - 10. Its density is 1.1 to 1.25 g/cm3. (e) The polyethylene wax The polyethylene wax emulsion used in this formulation is a - white translucent emulsion having 34 - 36% solid content, pH 8.0 - 10.5 with typical particle size of 0.6 microns. The Drop point of the wax component is 138° C and hardness of wax dmm is 0.5 maximum. The organic resin film comprising: (a) 50 to 60 parts by volume styrene acrylic copolymer having solid content of 30%. This styrene acrylic cqpolymer was collected from manufacturer with the properties mentioned in Example 4. This resin was dissolved in deionized water to make 38% of solid content and then used in this formulation. (b) 25 to 35 parts of by volume of polyurethane resin (c) 5 to 10 parts by volume of chromate solution (d) 4 to 8 parts by volume of colloidal silica. (e) 4 to 8 parts by volume of polyethylene wax The high-speed stirrer was used for the mixing of the organic coating constituents. The addition of the constituents was in the order as given above and stirred for 3 hours continuously. COATING APPLICATION The above formulations were used for the passivation of the zinc coated steel sheet. The hot dip galvanized steel sheet was used for the above passivation. The coating was applied by passing the zinc-coated sheet through the thin organic coating formulation. A thin uniform layer of the coating was formed on the sheet surface. It was then passed through a set of squeeze roll and the coating layer was dried in a heating oven at a peck metal temperature of 50 - 80°C. It Is important that the amount of chromate in the coated surface be held in the range of 10 to 30 mg/m2 for colourless chromate coating. Below 10 mg/mg2, only the partial protection against white rusting was obtained, while above 30mg/m2 light yellow colour appeared. It was found that the 20 mg/m2 showed good corrosion protection with a resin coating weight of approximately. In all the formulations, the organic coating weight was kept approximately 1000 mg/m2 with a total chromium of approximately 20 mg/m2 on each side of the sheet surface. Corrosion Test The samples of examples 1 to 4 were tested under salt spray test. Specimens of size 150 x 100 mm were taken for salt spray test. The edges of the sheet were covered by lacquer to prevent the galvanic corrosion from the edges. Salt spray test was done in 5% sodium chloride solution as per ASTM B117. The sample evaluation was done after an interval of 24 hours. The thin organic coating coated samples passed 100 150 hours of salt spray resistance in term of 10% white rust appearance. Friction Test: The lubrication property on sheet was measured by sheet to die friction test. A constant sliding speed of 150 mm/min. and a sliding distance of 20 mm were used in all the experiments. Both the static and dynamic coefficients of friction were measured. It was found that the application of thin organic coated coating on minimum spangle galvanized sheet reduces the friction of coefficient. The coefficient of friction for minimum spangle hot-dip galvanized sheet was approximately 0.2 µm where as the coefficient of friction for thin organic coating coated minimum spangle hot-dip galvanized sheet was approximately 0.1 µm. The lower coefficient of friction improves the lubricity properties of the thin organic coating coated sheet. Anti Finger Properties Handling of the product results in fingerprints, an excellent anti-fingerprint property is imperative. The synthetic sweat formulation (Volvo method) used to evaluate the anti-finger property. Drop of synthetic swear was poured in the sheet surface kept in horizontal condition for an hour and then was washed out. The dullness of the surface was visually observed to measure the anti-finger properties. It was found that the samples give a satisfactory performance and no dullness was observed on the sheet surface. Paint Adhesion test: The compatibility of the thin organic costing coated product with the powder coating was examined. The samples was pretreated by conventional method and then powder coated. The powder coating thickness was approximately 60 µm. The following test was performed the examine the adhesion properties of the powder-coated samples. Impact Test: A load of 980 grams was impacted on the samples from a distance of 110 cm. and it was visually observed with magnifier for paint crack. No cracking was observed on or around the impact produced dimples and the sample considered as pass the test. Conical Bend Test: The thin organic coating coated samples was manually bent over the cylindrical rod having one end diameter of 6.4 mm. The panel was bend approximately 180°C around the mandrel at a uniform velocity in a time of 1 s. No cracking was observed in the test sample after the test. The samples considered as pass the test. WE CLAIM 1. A process of providing an enhanced corrosion resistant thin organic coating on zinc, chromated or zinc alloy coated steel sheet with white rust resistance, anti-finger print, lubricity, weldability and paint adhesion properties comprising the steps of preparing: (a) a formulation of styrene acrylic copolymer by charging sodium metabisulphite dissolved in deionized water (DIW), a mixture of sodium lauryl sulphate, alkylaryl polyether (HYOXYD 400) dissolved in DIW and potassium persulphate or ammonium persulphate or hydrogen peroxide dissolved in DIW was charged into a reaction vessel at > 100 rpm preadded with DIW and maintained at 75°C; then adding a monomer mixture into the reactor vessel and a catalyst emulsifier mixture are added slowly by dropwise method for 2 hours under nitrogen atmosphere; allowing the polymerization reaction for another 2 hours; increasing the temperature of the reaction vessel to 85°C and kept at this temperature for 30 minutes to complete the reaction; cooling the vessel to room temperature; filtering the emulsion thus formed and adjusting the pH of the resulted acrylic emulsion to 7 to 9 on addition of sodium hydroxide,ammonia or triethanolamine, the solid content of the resulted resin formation being 38%; (b) preparing a chromate solution formulation by dissolving ammonium dichromate compound in de-ionized water (DIW) and pH of the resultant solution being maintained at 7.0-8.5 on addition of sodium hydroxide; (c) using soft dispersion of fine particle size polyurethane resin of 25- 35% solid content being maintained at pH 6.5 to 8; (d) using colloidal silica solution of solid content 15 to 30% and average particle size 4-15 mm, being maintained at pH 6.5 to 8; and (e) using a polyethylene wax emulsion having 30 to 36% solid content, maintained at pH 8.0 to 10.5 with particle size 0.6 microns; (0 By using the above five constituents, preparing a mixture on high speed stirring for 3 hours to make an organic coating solution by adding in order 50 to 60 parts by volume of styrene acrylic copolymer of step (a), 20 to 35 parts by volume of polyurethane resin solution from step (c), 5 to 10 parts by volume of chromate from step (b), 2 to 8 parts by volume of colloidal solution from step (d) and 2 to 8 parts dry volume polyethylene wax emulsion from step (e); (g)forming a thin uniform layer of coating of the resulted mixture on zinc and zinc alloy coated surface by means of dip coating, spray coating followed by squeezing or roller coater or other means of coating application; (h)the coated layer then being dried in a heating oven or other means of drying at peak metal temperature of 50-150°C produce a corrosion resistant thin coating on coated steel sheet followed by characterize evaluation through corrosion test, friction test, anti- finger properties test and paint adhesion test through impact and conical bend test. 2. The process as claimed in claim 1, wherein said monomers are selected from styrene, methyl methacrylate, methacrylic acid, acrylic acid, itaconic acid, butyl acrylate, ethyl hexyl acrylate and ethyl acrylate. 3. The process as claimed in claim 1 wherein the redox initiator selected from potassium persulphate, ammonium persulphate and hydrogen peroxide. 4. The process as claimed in claim 1, wherein the rate of addition of monomers to the reactor is in the range of 45 minutes to one hour per 200 grams of the monomer mixture. 5. The process as claimed in the claim 1, wherein the rate of addition of initiator and emulsifier mixture to the reactor is in the range of 45 minutes to one hour per 200 grams of the initiator emulsifier mixture. 6. The process as claimed in claim 1, wherein economically available styrene acrylic copolymer with following properties like stabilization emulsifier, styrene-acrylic monomers 40-50% solid content, Brookfield viscosity 20-70 at 30°C , pH 7.0- 9.5, specific gravity 1.1 to 1.2 at 30°C may be used as part of formulation to provide adequate coating performance in place of acrylic resin. 7. The process as claimed in claim 1, wherein the commercial styrene acrylic copolymer 50 to 60 volume parts mixed with a) polyurethane resin of 20- 35 volume parts, b) chromate solution 5-10 volume parts, c) colloidal silical 2-8 volume parts, d) poly-ethyline wax 2-8 volume parts are added. 8. The process as claimed in claim 1, wherein the thin organic coating is applied by dip coating, spray coating, roller coating on hot dip zinc and- zinc alloy coated sheets giving a dry coating weight of 500-3000 mg/m2 on each side and a total chromium weight of 10-50 mg/m2 per side. 9. A process as claimed in claims 1 and 7, wherein the amount of total chromium on each side of the coating maintained at 10 to 30 mg/m2 with a resin coating weight of 1000 mg/m2 provides good corrosion protection with colourless coating. 10. A process of providing an enhanced corrosion resistant thin organic coating on zinc or zinc alloy coated steel sheet substantially as herein described. A novel process for the development of corrosion resistance thin organic coating for zinc coated steel, comprising the steps of: - formulating a water soluble emulsion comprising a water based styrenated acrylic copolymer emulsion, polyurethane resin and rust preventive additives for use as white rust corrosion resistant coating by carrying out polymerizing reaction of acrylic monomers and redox initiators at a temperature 75°C-85°C for a period of 3 to 4 hours; - cooling the formulation; - adjusting the pH value of said styrenated acrylic copolymer to the range of 7 to 9; and - applying the formulation on zinc and zinc alloy coated steel in a thin layer.

Documents:

430-KOL-2005-(05-12-2011)-FORM-27.pdf

430-kol-2005-granted-abstract.pdf

430-kol-2005-granted-claims.pdf

430-kol-2005-granted-correspondence.pdf

430-kol-2005-granted-description (complete).pdf

430-kol-2005-granted-examination report.pdf

430-kol-2005-granted-form 1.pdf

430-kol-2005-granted-form 13.pdf

430-kol-2005-granted-form 18.pdf

430-kol-2005-granted-form 2.pdf

430-kol-2005-granted-form 3.pdf

430-kol-2005-granted-form 5.pdf

430-kol-2005-granted-gpa.pdf

430-kol-2005-granted-reply to examination report.pdf

430-kol-2005-granted-specification.pdf