FIELD OF THE INVENTION
This invention relates to an eco-friendly, chromium-free corrosion resistance
polymer coating composition for metallic surfaces such as galvannealed,
galvanized or cold rolled steel substrate. More particularly, the invention relates
to an eco-friendly water based corrosion resistance coating composition for steel
substrate providing 200 h of white rust resistance on galvanized and
Galvannealed steel substrate.
BACKGROUND OF THE INVENTION
Metals such as iron, aluminum, copper and magnesium and their alloys have
wide applications in different industrial and household components. These metals
are useful in industry because of their stiffness and high strength to weight
characteristics, but they are highly susceptible to corrosion in aggressive
environments. Corrosion is the major reason of energy and material loss. In spite
of much advancement in the field of corrosion science and technology, the
phenomenon of corrosion (mainly of Fe, Al, Cu, Zn, Mg and their alloys) remains
a major concern to industries around the world. There are highly corrosion
resistant materials but the cost becomes the constraint on use of these
materials. Hence, use of cheap metallic materials along with efficient corrosion
prevention methods is researched for years in many industrial applications.

To reduce the corrosion at least, two approaches are known to be utilized: for
example, passive corrosion protection and active corrosion protection. Passive
corrosion protection is normally provided by a barrier film that prevents contact
of corrosive species with the metal surface and therefore hinders the corrosion
process. However, in the cases when a defect is formed in the barrier layer, the
coating cannot stop corrosion in this place. The second approach is active
corrosion protection, which employs inhibitive species that can decrease
corrosion activity.
Industrial protection systems comprise different layers such as pre-treatment,
primer and top coating. Pre treatment plays an important role of intermediate
layer that increases adhesion between the metal surface and the organic coating
and also provides an additional barrier and, eventually, active corrosion
properties. Chromate conversion coatings have been used as pre treatments for
a long time due to a good adhesion as well as active corrosion protection.
However, the use of chromates has been an environmental hazard because of
the carcinogenic activity and toxicity. A generic way to protect metals from
corrosion is to apply protective films coatings. The protective film coatings allow
the desired properties of the substrate to be coated through a chemical
modification of the coatings, such as mechanical strength, optical appearance
etc. There are several techniques for the deposition of coatings on metals,

including physical vapour deposition, chemical vapour deposition, electrochemical
deposition, plasma spraying and sol-gel process.
The sol-gel process is a chemical synthesis method described as the creation of
an oxide network by progressive condensation reactions of molecular precursors
in a liquid medium. There are two ways to prepare sol-gel coatings: the inorganic
method and the organic method. The inorganic method involves the evolution of
networks through the formation of a colloidal suspension and gelation of the sol
to form a network in continuous liquid phase. Organic phase is the most widely
used, which starts with a solution of monomeric metal or metalloid alkoxide
precursors M (OR)n in an alcohol or other low molecular weight organic solvent.
Here M represents a network forming element, such as Si, Ti, Zr, Al etc. and R is
typically an alkyl group.
The sol-gel formation occurs in four stages: (a) hydrolysis (b) condensation and
polymerization of monomers to form chains and particles (c) growth of the
particles (d) agglomeration of the polymer structures followed by the formation
of networks that extend throughout the liquid medium resulting in thickening,
which forms a gel. Hydrolysis and condensation reactions occur simultaneously.
A sol-gel coating can be applied to a metal substrate through various methods,
such as dip-coating and spin coating, which are most commonly used.

Furthermore, in order to improve the performance of these silica sol-gels,
corrosion inhibitors are added. The purpose of this approach is to avoid the
leaching of the inhibitor from the zones of corrosion.
Prior Art
JP2007070572 discloses a coating material composition that has improved rust
prevention property in the heat affected zone. The composition includes an acryl
amino type thermosetting resin, a silicate compound and thiazole type
compound, and/or silane coupling agent.
KR20090070024 discloses a chromium-free processing liquid based upon a
binder resin, silicate, silane, titanium, urethane resin and epoxy resin, titanium
carbonate, and titanium phosphate. The invention claims chromium-free surface-
treated steel plate for use in fuel tank and comprises chromium-free layer and
electro-galvanized zinc-based metal plated steel sheet.
Patent applications KR20090065020 and WO2007075050 also disclose surface
treated Cr-free steel sheet for use in a fuel tank. All these disclosed inventions
teach corrosion protection of 24-48 hours on galvanized sheet. The dry film
thickness of the coated galvanized sheet is in the range of 5-30 micron meter
and wet coating dry at more than 100 deg C.

Indian patent application number: 1328/KOL/2012 describes a water based
coating which can provide 500 h red rust corrosion resistance on Galvannealed
substrate and the same coating solution show only 48 h of white rust resistance
on Galvannealed substrate and provide less than 24h of white rust resistance on
galvanized substrate.
Although, quite a few formulations are known in the art, a need still exists for
formulations that can provide corrosion resistance for higher durations. In light
of the above discussed prior art, there is a need for chrome free coatings having
high corrosion resistance and good adhesion property, at low film thickness,
preferably less than equal to 5 micron thickness. Further, the coating should be
capable for easy-application on Galvannealed and galvanized steel substrate by
well known techniques such as spray, brush and roll coater. Further, the chrome
free coating should have good forming properties including fast drying property
on the metallic substrate, preferably at below 90 deg C.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose an eco-friendly
water based corrosion resistance coating composition for steel substrate
providing 200 h of white rust resistance on galvanized and Galvannealed steel
substrate.

Another object of the present invention is to propose an eco-friendly water based
corrosion resistance coating composition for steel substrate providing 200 h of
white rust resistance on galvanized and Galvannealed steel substrate, which is
resistant to petrol and diesel.
Still another object of this invention is to propose an eco-friendly water based
corrosion resistance coating composition for steel substrate providing 200 h of
white rust resistance on galvanized and Galvannealed steel substrate, that allows
uniform coating on the steel surface, when applied by spray, brush, dip or roll
coater.
Yet another object of this invention is to propose an eco-friendly water based
corrosion resistance coating composition for steel substrate providing 200 h of
white rust resistance on galvanized and Galvannealed steel substrate, which gets
dried below 90° Centigrade within 10 to 30 seconds.
A further object of the invention is to propose a steel sheet coated with an eco-
friendly chromium free coating.
A still further object of the invention is to propose a fuel tank coated with
chromium free anti-corrosive coating.

DETAILED DESCRIPTION OF THE INVENTION
According to this invention, there is provided an eco-friendly corrosion resistance
coating for steel or metallic substrates that comprises 10-90% by weight of
water based poly condensed hybrid reaction product of a silane solution , 0.5-5%
by weight of a hydrolysing agent, 0.1-3% by weight of a flash rust inhibitor,
0.05-5% by weight of a curing agent, 0.5 -30% film forming agent, 0.5 - 20%
pigment and 0.0- 2% defoamer and leveling agent. The remaining portion of the
coating is water based upon 100 percent by weight of the total coating
composition.
According to the invention, one or more of the objectives of the invention may
be achieved by applying the eco-friendly coating on steel substrate. The eco-
friendly coating comprising at least one organofunctional silanes group applied
on to the steel substrate. Thereafter, the coating mixture is cured so as to
provide a dense network structure of coating for protection of the substrate from
corrosion and gasoline environment.
The primary organofunctional silane compound used in the embodiments of the
invention includes hybrid condensation product of water soluble sol-gel solution
prepared from a solution containing one or more organofunctional silanes. In one
embodiment, organofunctional silanes such as glycidoxypropyltrimethoxysilane
(GPTMS) 0.5 - 20 wt %, tetraethoxy silane (TEOS) 0-5 wt %, vinyl trimethoxy
silane (VTMS)O.l - 20%,mercaptopropyl trimethoxy silane 0.5- 10 wt %. and

aminopropyl triethoxy silane 0.1- 10 wt% are used. Besides the organofunctional
group, it also contains organic functionality based on Si bond epoxy group. The
above silane solution is hydrolised at pH 4-6.5 for 16 h at room temperature with
continuous stirring at a speed of 300-800 rpm.
The hydrolysing agent is used to hydrolyse the silane compound and to create
free hydroxyl group, which free hydroxyl group form a chemical bond between
the polymer and metal. The hydrolysing agent used in the present invention is
one of hydrochloric acid, nitric acid, acetic acid, and formic acid, but not limited
to the exemplary agents.
The coating mixture may comprise 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 may be used as per the present invention include compounds such as
sodium nitrite, benzotriazole and a mixture of one or more of 10-25% of C12-C14
(2-benzothiazolylthio) succinic acid tertiary amine salts, 10-25% of ethoxylated
tridecylalcohol phosphate-comprising monoethanolamine salts, 10-25% of zinc
salts of branched (C6-C19) fatty acids, <2.5% of zinc salts of naphthenic acid, 10-
25% morpholine benzoate. The flash rust inhibitor used in the present invention
has the following physical properties:

Density (200C) : approx. 1.04 gm/ cm3
viscosity (200C) : < 200 mPa.s
pH-value: 8-10
Curing agent is used to accelerate the rate of reaction and to reduce the curing
temperature. The present invention includes curing agent but is not limited to
polycabodiimides, aziridines , butyl diethanol amine or any combination thereof.
The present invention includes a film forming agent, which adsorbes on steel
substrate and enhances the film thickness of the applied coating. This film
forming agent includes but is not limited to ethylene glycol, polyethylene glycol,
ethyl silicate or any combination thereof.
In another embodiment of the invention, the coating mixture may comprise a
corrosion resistance pigment. Preferred examples of the corrosion resistance
pigments as per the present invention include nano zinc oxide, nano silica, nano
alumina, nano cerium oxide, zirconium nitrate, lithium nitrate, zinc phosphate,
zinc phosphate derivatives or any combination thereof.
The eco-friendly corrosion resistant coating of the invention can be applied to
steel substrates using any of well-known coating methods such as dipping,
spraying, roll coating and brush coating. The coating weight of the composition
is not particularly limited. However, the coating is applied so as to give a coating
thickness in the range of 500nm to 200 micron.

EXAMPLES:
The present invention will be described with reference to the following examples.
These examples are provided only for illustrating the present invention and
should not be construed as limiting the scope of the present invention.
Commercially available Galvannealed and galvanized steel substrate was used as
the metal material for applying the coating of the present invention.

The coating formulation of example 1 when applied on galvanized steel substrate
provides uniform coating with 0.5 to 2 micron dry film thickness. The coating
formulation provided SST life in the range of 24-72 hours as per ASTM B117
standard.


The coating formulation of example 2 when applied on Galvannealed steel
substrate provides uniform coating with 0.5 to 10 micron dry film thickness. The
coating formulation provided more than 200 h white rust resistance life as per
ASTM B117 standard. Also, the coated Galvannealed steel sheet provides more
than one year resistance to petrol and diesel in static immersion conditions. The
coating formulation of example 2, when applied on galvanized steel substrate
provides uniform coating with 0.5 to 10 micron dry film thickness. The coating
formulation provides corrosion resistance of 24 to 200 h salt spray resistance for
white rust resistance as per ASTM B117 standard.
The disclosed eco-friendly coating of the present invention provides a very good
adhesion and corrosion resistance to Galvannealed and galvanized steel
substrate. Further, the coated galvannealed and galvanised steel substrate is
weldable and formable and can withstand corrosion resistance to petrol, diesel
and acidic environment.

The present invention is about the development of new coating chemistry which
can applied on galvanized and galvannealed steel substrate to provide more than
200h of white rust resistance at a coating thickness of less than 5 micron and
can dry within 10-30 sec at 80-90 deg C peak metal temperature.
This coating formulation can be applied on Galvannealed, galvanised, Al and Cu,
Sn substrate and has a high potential to replace chrome pretreatment process.

WE CLAIM:
1. A chromium-free coating composition for treating a metal-surface, the coating
composition comprising:
10-90 percentage by weight of a water based poly condensed silane
solution comprising of one or more organo-functional silanes;
0.5-5 percentage by weight of a hydrolysing agent;
0.1-3 percentage by weight of a flash rust inhibitor;
0.05 - 5 percent by weight of a curing agent;
0.5 - 30 percent by weight of a film forming agent;
0.5- 20 percent by weight of a pigment;
0-2 percentage by weight of a defoamer and a leveling agent; and
the balance being water based upon 100 percent by weight of the total
coating composition.
2. The coating composition as claimed in claim 1, wherein the hydrolysing agent
is selected from a group consisting of hydrochloric acid, nitric acid, and acetic
acid.
3. The coating composition as claimed in claim 1, wherein the one or more
organofunctional silanes includes glycidoxypropyltrimethoxysilane (GPTMS) 0.5 -
20 wt %, tetraethoxy silane (TEOS) 0-5 wt %, vinyl trimethoxy silane (VTMS) 0.1
- 20%, mercaptopropyl trimethoxy silane 0.5- 10 wt %. and aminopropyl
triethoxy silane 0.1- 10 wt%.

4. The coating composition as claimed in claim 1, wherein the water based poly
condensed silane solution comprising of one or more organo-functional silanes is
hydrolised at pH 4-6.5 for 16 hours at room temperature with continuous stirring
at a speed of 300-800 rpm.
5. The coating composition as claimed in claim 1, wherein the flash rust inhibitor
is sodium nitrite, benzotriazole and a mixture of one or more of 10-25% of C12-
C14 (2-benzothiazolylthio) succinic acid tertiary amine salts, 10-25% of
ethoxylated tridecylalcohol phosphate-comprising monoethanolamine salts, 10-
25% of zinc salts of branched (C6-C19) fatty acids, <2.5% of zinc salts of
naphthenic acid, 10-25% morpholine benzoate.
6. The coating composition as claimed in claim 1, wherein the curing agent is
butyl diethanol amine or its derivatives.
7. The coating composition as claimed in claim 1, wherein the film forming agent
is selected from the group consisting of ethylene glycol, poly ethylene glycol,
ethyl silicate and a mixture thereof.
8. The coating composition as claimed in claim 1, wherein said leveling and
defoamer is silicon solution or its derivatives.
9. The coating composition as claimed in claim 1, wherein the coating
composition further comprises a pigment.

10. The coating composition as claimed in claim 1, wherein the pigment is
selected from the group consisting of zinc oxide, silica, alumina, cerium nitrate,
cerium dibutyl phosphate, zirconium nitrate, lanthanum nitrate and a
combination thereof.
11. A steel substrate coated with the chromium-free coating composition as
claimed in claim 1.
12. A fuel tank coated with the chromium-free coating composition as claimed in
claim 1.
13. The steel substrate as claimed in claim 11, wherein thickness of the coating
composition is in the range of 500 nm to 200 micron.
14. The fuel tank as claimed in claim 12, wherein thickness of the coating
composition is in the range of 500 nm to 200 micron.
15. The steel substrate as claimed in claim 11, wherein the steel substrate is a
galvannealed steel substrate.
16. The steel substrate as claimed in claim 11, wherein the steel substrate is a
galvanized steel substrate.

17. The coating composition as claimed in the claim 1, wherein pH of the coating
composition is in the range of 3 to 9.
18. The coating composition as claimed in claim 1, wherein the coated metal-
surface is weldable.

ABSTRACT

A chromium free water based coating is developed for treating Galvannealed or
galvanized steel surface. The coating is based upon hybrid condensation product
of water soluble sol-gel solution prepared from solution containing one or more
organofunctional silanes. The said silane solution is hydrolised at pH 4-6.5 for 16
hours at room temperature with continuous stirring at a speed of 300-800 rpm.
The coating composition when applied on a galvanized and galvannealed steel
substrate provides more than 200 hours of white rust resistance at a coating
thickness of less than 5 micron and can dry within 10-30 sec at 80-90 deg C
peak metal temperature.