Title: Organic inorganic hybrid coating composition for galvanized item.
FIELD OF INVENTION:
The invention relates to the development of organic and inorganic chemical based hybrid coating composition for protection and durability of galvanized products.
This invention also relates to a process for preparing organic and inorganic chemical based coating composition comprising adding the constituents in a particular sequence under stirring for about 1 hrs and subjecting the mixture to the step of filtering by approximately 300 urn filter cloth.
BACKGROUND OF THE INVENTION:
Galvanized items are commercially produced by hot-dip zinc coating to improve the corrosion resistance of steel items by barrier and galvanic action of zinc coating. When galvanized product exposed in the natural atmosphere, many corrosion cells are formed on the surface and thereby corrosion product are generally formed. The effective corrosion products are Zn(OH)2 and basic zinc salts. Basic zinc salts are formed in atmospheres characterized by species such as CO2, NaCI and SOx. That is 2ZnCO3.3Zn(OH)2 in mild atmosphere, ZnCl24Zn(OH)2 and ZnCI2.6Zn(OH)2 in chloride atmosphere and ZnSO4.4Zn(OH)2 in SOx atmosphere. The stability of zinc salts depends on the pH and anion concentration of electrolyte on galvanized surface influenced by the environment.

The conventional method for increasing the life of Gl product is to increase the zinc coating weight. However, this increase the product cost as zinc is a costly metal. Another approach is to apply a chromate passivation on galvanizing item but it will only make a little improvement on coating life because mechanical aberration during mesh, barbing and fencing operation deteriorate the chromate coating.
The present invention describe a organic-inorganic hybrid coating composition which can be applied in a continuous galvanizing line as a post treatment coating over galvanized item. The developed organic-inorganic hybrid coating provides an excellent corrosion resistance, paint adhesion, lubrication, and anti-fingerprints properties and allows a practical level of grounding and weldability. The formulation consists of organic resins and soluble chromium compound along with other additives.
OBJECTS OF THE INVENTION:
An object of this invention is to propose an organic and inorganic chemical based coating for galvanized product.
Another object of this invention is to prevent corrosion of galvanized product during exposure to environment.
Still another object of this invention is to add lubrication to the galvanized item through the coating.
Further object of the invention is to incorporate paint adhesion in galvanized product.

Still further object of this invention is to resist any impression due to finger print during handling.
DETAIL DESCRIPTION OF THE INVENTION:
According to this invention an organic and inorganic chemical based coating composition comprising the following constituents:
a) Styrene acrylic emulsion having basic properties of 25-55 wt% solid, pH 7-9.0, particle size 0.05-0.5 urn, sp.Gr.1.01-1.2, white milky appearance.
b) Polyurethane dispersion, high molecular weight polymer having 25-50 wt% solid pH 8.0-10, viscosity 50-500 cps.
c) Nano silica sol (colloidal silica) 15-30% solid content, particle size 4-15 nm pH 9.5-10, density 1.1-1.259/cm3.
d) Polythene wax emulsion, a white, translucent non-ionic or cationic emulsion having 15-40% solid content pH 3.0-10 with particle size of 0.6 microns.
e) Chromium compound, sodium hydroxide and some additives such as antifoaming, dispersing agent and the rest is water.
In accordance to this invention a process for preparing organic and inorganic chemical based coating composition comprising adding the constituents in a particular sequence under stirring for about 1 hrs and subjecting the mixture to the step of filtering by approximately 300 urn filter cloth.
The organic-inorganic hybrid coating composition and development of the product has been achieved using the commercially available constituents, comprising mainly, styrene acrylic emulsion, polyurethane dispersion, soluble chromium, nano silica sol and polythene wax.

The specification of the constituents and their selection are processed as under.
a) The typical properties of the commercially available styrene acrylic emulsion are: 40-50 wt% solid, pH 7.5-9.0, particle size 0.05-0.15 urn, sp. Gr. 1.01-1.09, and white milky appearance. This styrene acrylic emulsion was dissolved in water under high stirring condition to make 30% solid content and then filtered it with 300 urn filter cloth.
b) The polyurethane dispersion is a high molecular weight polymer that is dispersed in water by neutralizing the carboxylic acid groups in the backbone. The typical properties of polyurethane dispersion are: 30-50 wt% solid, pH 9.0-9.5, viscosity 50-500 cps, particle size 0.150 urn, anionic particle charge, TEA neutralizing amine, white milky appearance. This polyurethane dispersion was dissolved in water under high stirring condition to make 25% solid content and then filtered it by 300 urn filter cloth.
c) The nano silica sol (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 9.0-10. Its density is 1.01 to 1.25 g/cm3.
d) The polyethylene wax emulsion used in this formulation is a -white translucent non-ionic 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.
e) The commercial grade ammonium dichromate was used in this formulation. It was dissolved in deionised water at a concentration of 150-170 gm/1 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.

The organic-inorganic hybrid coating composition was made from the above modified constituents given in (a) to (e). The constituents were added as per the sequence mentioned below under high stirring for eight hours and then filtered it by 300 pm filter cloth.
a) 35 parts by volume of styrene acrylic copolymer
b) 15 parts of by volume of polyurethane resin
c) 3 parts by volume of nano silica sol (colloidal silica)
d) 2.5 parts by volume of polyethylene wax
e) 3 parts by volume of chromate solution
The above composition was applied on galvanized wire in commercial galvanized line by dip coating process followed by high temperature drying.
The salt spray test was conducted as per ASTM B117 on organic-inorganic hybrid coated galvanized wire along with conventional galvanized wire. The galvanized wire of coating weight 30 gm/m2 was taken for study. The samples appearance is given in figure below after 168 hours of salt spray test. It is clearly visible that the organic-inorganic hybrid coated galvanized wire was intact and no red rust appeared on the galvanized wire surface. However, the conventional galvanized wire got red rusted. This indicate the organic-inorganic hybrid coating improves the corrosion resistance performance of the galvanized wire.

WE CLAIM:
1. An organic and inorganic chemical based coating composition comprising the following constituents:
a) Styrene acrylic emulsion having basic properties of 25-55 wt% solid, pH 7-9.0, particle size 0.05-0.5 urn, sp.Gr. 1.01-1.2, white milky appearance;
b) Polyurethane dispersion, high molecular weight polymer having 25-50 wt% solid pH 8.0-10, viscosity 50-500 cps;
c) Nano silica sol (colloidal silica) 15-30% solid content, particle size 4-15 nm pH 9.5-10, density 1.1-1.259/cm3;
d) Polythene wax emulsion, a white, translucent non-ionic or cationic emulsion having 15-40% solid content pH 3.0-10 with particle size of 0.6 microns;
e) Chromium compound, sodium hydroxide and some additives such as antifoaming, dispersing agent and the rest is water;
2. The coating product as claimed in claim 1, wherein the ratios and percentage of respective components by weight, ie 100 kg of the solid coating comprises
a) 15-25 kg of styrene acrylic resin;
b) 5-15 kg of polyurethane dispersion;
c) 05-3 kg of polyethylene wax;
d) 05-2 kg of colloidal silica;
e) 0.5-2 kg of chromium compound;
f) 200 to 500 gm of sodium hydroxide and additives and
g) the reminder is water.

3. The product as claimed in claims 1 and 2 wherein the pH strength of the final compound is 6.5 to 8.5.
4. The product as claimed in claims 1, 2 and 3, wherein the final product constitutes 20-40 kg of the solid percent by weight and the remaining part is water.
5. The product as claimed in claims 1 to 4, wherein the coating product is applied on the continuous galvanizing line either by dip, spray or roller method and subsequently dried on oven at the peak metal temperature of 60-120 degree centigrade.
6. The product as claimed in claim 1, wherein the chromium compound is selected from ammonium dichromate, sodium dichromate & potassium dichromate.
7. A process for preparing organic and inorganic chemical based coating composition comprising adding the constituents in a particular sequence under stirring for about 1 hrs and subjecting the mixture to the step of filtering by approximately 300 urn filter cloth.
8. The process as claimed in claim 7, wherein the sequence of the constituents as follows:

a) 35 parts by volume of styrene acrylic copolymer
b) 15 parts of by volume of polyurethane resin
c) 3 parts by volume of namo silica sol (colloidal silica)
d) 2.5 parts by volume of polyethylene wax
e) 3 parts by volume of chromate solution

9. The process as claimed in claim 7, wherein the said chromate solution is prepared by dissolving the chromate as herein described in deionised water at a concentration of 10-300 gm/l and the chromate solution made alkaline by adding sodium hydroxide to make pH + of 7-10.

An organic and inorganic chemical based coating composition comprising the following constituents: styrene acrylic emulsion having basic properties of 25-55 wt% solid, pH 7-9.0, particle size 0.05-0.5 urn, sp.Gr.1.01-1.2, white milky appearance; polyurethane dispersion, high molecular weight polymer having 25-50 wt% solid pH 8.0-10, viscosity 50-500 cps; nano silica sol (colloidal silica) 15-30% solid content, particle size 4-15 nm pH 9.5-10, density 1.1-1.259/cm3; polythene wax emulsion, a white, translucent non-ionic or cationic emulsion having 15-40% solid content pH 3.0-10 with particle size of 0.6 microns; chromium compound, sodium hydroxide and some additives such as antifoaming, dispersing agent and the rest is water.