TITLE:
Temporary rust preventive coating for steel (rebar) surface FIELD OF INVENTION
This invention relates to a rust preventive coating for steel surface.
This invention further relates to temporary protection coating composition for steels preferably TMT rebars for construction. Further, the invention specifically relates to a coating that can provide corrosion resistance against salty and humid environment. This invention not only provide the temporary protection but also gives shiny bluish look which help in product differentiation.
BACKGROUND OF THE INVENTION
Thermo mechanical treated rebars are commonly known as "TMT rebars" and its surface is exposed to open atmosphere. Due to the electrochemical reaction with the environment, the red rust is formed on the rebar surface. Although, it is not very detrimental from corrosion point of view, but aesthetically it is not acceptable to the customers. Hence, some post treatment of the rebar is required to prevent this early rusting process. The conventional nitrite or chromate coating is not sufficient to avoid early discoloration during transportation and storage. There are different methods available to reduce the corrosion rate of steel surface for a shorter period of time. Some of the well accepted and economical methods are as follow;

Thermoplastic coating: This can be applied by dissolving the thermoplastic resin in solvent medium. After the evaporation of solvent, a polymeric film developed on the surface of steel. Depending upon the chemistry and thickness of thermoplastic coating, steel substrate can be protected for some period of time. There are two major difficulties associated with this method, firstly, the removal of thermoplastic coating before any further application or fabrication of steel substrate and secondly the inherent solvent hazard associated with this method.
Use of rust preventing (RP) oils: Different types of rust preventive oils are available, which can be applied on the steel surface by dipping or spraying method. Depending upon the chemistry and inhibitors of RP oils steel substrate can be protected from corrosion for a period of 2-3 months. This method also needs proper protection from water and moisture, otherwise saponification and emulsification of RP oils will damage the surface quality of steel substrate.
Application of different inhibitors: There are different inhibitors like volatile corrosion inhibitors (VCI) and volatile protective inhibitors (VPI), which can continuously release anticorrosive vapor, metal come in contact with vapor form a protective film on metal substrate. However, this method is not economical for protection of large scale materials like rebar and coils.
Corrosion on rebar is a long lasting problem. A lot of work has been done to improve the corrosion resistance property of rebar by applying different types of coatings. Research work has been done on different types of phospating, plating and polymeric compound based coatings.

Inorganic materials based coating
CN101948264 uses the corrosion inhibitor comprises sodium mono-fluorophosphate, calcium gluconate, gas phase corrosion inhibitor and water. CN102491668 uses Corrosion inhibitor comprises of silicate, aluminum acid salt, organic amine, and gluconic acid. CN1062559 provides the uses of Fe(OH)3-((OH)3, NaOH, NaN03, Na2Si03, Na2Cr204 to protect rebar from rusting. IN2003DE01187 utilises of sodium hydroxide, sodium citrate, sodium stannate, calcium oxide aginst the corrosion of rebars
Organic Materials based coating
CN102173639 provided the polycarbonate based coating for reinforcing steel bar preventing from corroding. The polycarbonate generated by modified ether polycarboxylic acid water reducer as base, adjusting pH for water reducer using alkylol amine organic monomers and mixing with hydroxy acid salt. CN102070787 uses conductive polymer gel using acrylamide-acrylic acid copolymer as matrix material involves acrylamide, acrylic acid, N,N'-methylenebisacrylamide and fluoroboric acid to solution for rebar corrosion prevention. CN102199014 utilizes inhibitor, nitrite compound, nano silicon oxide in poly vinyl alcohol coating to give protection to TMT rebars.
Vapor Phase inhibitors
CN102021581 uses metallic vapor-phase inhibitor, comprises of sodium bicarbonate, diammonium hydrogen phosphate, sodium nitrite, naphthol antirust additive, gelatin, alcohol. CN1603469 involves nvironment-friendly vapor phase corrosion inhibitor, comprises of malic acid morpholine, Triethanolamine borate, hexamethylene tetramine.

OBJECTS OF THE INVENTION:
An object of the present invention is to propose a temporary rust preventive coating for steel surface.
Another object of the present invention is to prepare an eco-friendly water based corrosion resistance coating for TMT rebar which can provide temporary protection up to one year during storage and transportation.
Another object of the present invention is to prepare a coating for TMT rebar surface which can provide resistance to saline and humid environment.
Still another object of the invention is to develop an eco-friendly coating that provides a uniform coating on the steel surface, when applied by spray or dipping process.
Further object of this invention is to provide an eco-friendly coating composition which can dry fast.

Still further object of the invention is to provide a coating on TMT rebar without any surface preparation like acid pickling, soak cleaning, and water rinsing.
Yet another object of the invention is to provide a temporary protection on rebar which should not reduce the bonding strength of rebar with concrete material.
BRIEF DESCRIPTION OF THE INVENTION
According to this invention there is provided a temporary rust preventive coating formulation comprising:
1 to 25% by wt. of an inorganic silicate solution;
1 to 50% by wt. of an acrylic polyurethane copolymer resin solution;
0.25 to 0.75% by weight of a flash rust inhibitor;
0.5 to 1.5% by weight of a curing agent;
0.5 to 1.5% by weight of a wetting agent and
remaining being de-mineralized water.
A specialized coating was developed to protect the rebar surface from red rusting temporarily period of up to one year. This coating doesn't require surface protection and it can apply through dip or spray coating. Also it doesn't need high temperature curing and can be cured at ambient temperature.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING-
Fig 1: shows the atmospheric exposure of coated and uncoated rebars.
DETAILED DESCRIPTION OF THE INVENTION
The problem of red rusting of the rebar till it reaches to customers a cost effective and specialized barrier coating film was developed on the rebar surface. The said coating solution can be applied by dip, spray and any other method. This coating on the rebar surface is not peeling off even after bending.
According to this invention, there is provided an eco-friendly corrosion resistance coating for steel or metallic substrates that comprises 1 to 25% by weight of water based inorganic silicate polymer, 1 to 50% acrylic polyurethane copolymer resin, 0.25 to 0.75% by weight of a flash rust inhibitor, 0.5 to 1.5% by weight of a curing agent, 0.5 to 1.5 % by weight of a wetting agent, The remaining portion of the coating is water based upon 100 percent by weight of the total coating composition.
In accordance with an embodiment of the invention, the acrylic polyurethane copolymer resin solution has preferably 8-10 wt% in final coating solution.
The flash rust inhibitor in an embodiment is amphoteric based and have heterocyclic compound, Nitrate, phosphate and silicate.

The curing agent is selected from a group consisting of imidazolegroup or its derivatives, butyl diethanol amine and a mixture thereof.
The said wetting agent is used is amine, stearate salt and hydroxyl based.
According to the invention, one or more of the objectives of the invention may be achieved by applying the eco-friendly coating on TMT rebar substrate. The eco-friendly coating comprising at least one silicate group is applied on TMT substrate. The present invention includes compounds such as sodium silicate or its derivatives. In an embodiment of the invention, potassium lithium silicate based resin is used. Thereafter, the coating mixture is cured so as to provide thermosetting network structure of coating for protection of the substrate from corrosion.
The coating mixture comprises an aqueous solution of flash rust inhibitor. The flash rust inhibitor is used to restrict or delay the onset of under film corrosion or pre cure corrosion. Preferred examples of the flash rust inhibitors that can be used as per the present invention include compounds such as sodium nitrite, benzotriazole, and sodium gluconate or any combination thereof.
Curing agent is used to accelerate the rate of reaction and to reduce the curing temperature. The present invention includes curing agent such as imidazole group or its derivatives or butyl di-ethanol amine or any combination thereof.
The present invention includes a film forming agent, which adsorbed or absorbed on steel substrate and enhanced the film thickness of applied coating. This film forming agent includes ethylene glycol or poly vinyl alcohol or ethyl silicate or any combination thereof.

The eco-friendly corrosion resistant coating of the invention can be applied to steel substrates such as TMT rebars using any of well-known coating methods such as dipping or spraying. However, the coating is applied so as to give a coating thickness in the range of 1 to 10 urn (when measured by weight difference method).
Example 1
Coating Ingredient Composition by weight %
Acrylic polyurethane copolymer resin: 15%
Potassium lithium silicate: 5
Sodium Nitrite: 0.25
Ethyl silicate: 1
Butyl di-ethanol amine: 1
Water: Remaining
The coating formulation of example 1 when applied on TMT steel rebar substrate provides uniform coating and dry within 10 minutes at 35°C. The coating formulation provided dry film thickness of 1-10 urn (when measured by weight difference method) and less than 120 hours red rust resistance life as per ASTM B117 standard.

Example 2:
Coating Ingredient Composition by weight %
Acrylic polyurethane copolymer resin: 15%
Potassium lithium silicate: 10
Sodium Nitrite: 0.25
Ethyl silicate: 1
Butyl di-ethanol amine: 1
Water: Remaining
The coating formulation of example 2 when applied on TMT rebar substrate provides uniform coating with dry film thickness of 5-15 um( when measured by weight difference method) and dry within 10 minutes at 35°C (tested as per ASTM D5859). The coating formulation provided more than 120 h red rust resistance life as per ASTM B117 standard.
The disclosed eco-friendly coating of the present invention provides a very good adhesion (showing 5B rating as per ASTM D3359 test) and temporary corrosion protection to TMT rebars substrate. Further, the coated TMT rebar is not reducing the bond strength with concrete, as compared to bond strength of uncoated rebar with same concrete (as shown in figure1).The new coating on TMT rebar can be applied by dipping or spraying process and dries within 10 minutes at 35°C. Above preferred examples of coatings on TMT rebars are given to illustrate the

invention however, coating formulation can be used on any other steel ;8substrates as well where temporary corrosion resistance is needed. The above given examples should not be construed as limiting but rather enabling the invention.

WE CLAIM:
1 A temporary rust preventive coating formulation comprising: 1 to 25% by wt. of an inorganic silicate solution; 1 to 50% by wt. of an acrylic polyurethane copolymer resin
solution;
0.25 to 0.75% by weight of a flash rust inhibitor; 0.5 to 1.5% by weight of a curing agent; 0.5 to 1.5% by weight of a wetting agent and remaining being de-mineralized water.
2. The coating formulation as claimed in claim 1, wherein the said inorganic silicate solution is potassium lithium silicate and or its derivative.
3. The coating formulation as claimed in claim 1, wherein the said acrylic polyurethane copolymer resin solution have preferably 8-10 wt% in final coating solution.
4. The coating formulation as claimed in claim 1, wherein the said flash rust inhibitor is amphoteric based and have heterocyclic compound, Nitrate, phosphate and silicate.

5. The coating formulation as claimed in claim 1, wherein the said curing agent is selected from a group consisting of imidazolegroup or its derivatives, butyl diethanol amine and a mixture thereof.
6. The coating formulation as claimed in claim 1, wherein the said wetting agent is amine, stearate salt and hydroxyl based.
7. The coating formulation as claimed in claim 1 further comprises a film forming agent, the a film forming agent being selected from a group consisting of ethylene glycol, poly vinyl alcohol, ethyl silicate and a combination thereof.
8. The coating formulation as claimed in claim 1, wherein the
coating formulation is applied over TMT rebar.