FIELD OF THE INVENTION
This invention relates to an eco-friendly, thin polymer based chromium-free
corrosion resistant polymer coating composition for galvanized and galvannealed
steel substrate. More particularly, it relates to preparation of a silane solution for
coating by sol-gel technique.
BACKGROUND OF THE INVENTION
Corrosion is a well-known problem relating to metallic structure like steel. Different
approaches were involved in order to prevent or reduce corrosion. Out of different
approaches, protective coating on metal surface plays an important role. Protective
coating for steel sections is typically based upon paints, organic layers, ceramic and
inorganic layers, plastic lining and electroplating.
Among all barrier protection methods painting and chemical conversion coatings are
cost effective, less sophisticated and widely used because of high speed of coating
formation and good adherent nature.
In chemical conversion coatings a thin film of certain chemical solution is adhered on
the surface of metal. Based on the main constituent present in the coating solution
chemical conversion coatings processes are of many kinds viz. phosphating,
chromating and oxalating.
Sol gel is also one of the unique processes for synthesizing polymeric coating. Sol gel
is a process where two or more molecules couple each other by hydrolysis followed
by condensation process. Chromates in chromic acid sealing are very important for
increasing passivity, reducing porosity and in improving the paint film adhesion.
However various occupational and health hazard problems associated with chromium
effluent disposal make it difficult to use at large scale.

The literatures had shown that effect of pH in sol-gel process and concluded that it
is only the pH of the solution which plays major role in hydrolysis process and
negative part of the acid does not play any role.
Patent application CN103966590 explored the sol-gel with different additives based
coating solution for galvanic plating wire surface. The effectiveness of the coating in
terms of white rust resistance is missing. However the coating application methods
and feasibility of coating on large scale is not described. The sol-gel chemistry and
hydrolyzing effect is also not explored.
OBJECTS OF THE INVENTION
In view of the foregoing limitations inherent in the prior-art, it is an object of the
invention to develop a chrome free coating which has high corrosion resistance and
good adhesion property.
Another object of the invention is to prepare an eco-friendly corrosion resistance
coating for steel substrate.
Another object of the invention is to prepare an eco-friendly corrosion resistance
coating for steel substrate.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a method for making a Poly-condensed silane
by mixing amino propyl tri-methoxy silane (AMEO) with 3-gycosidoxy propyl tri-
methoxy silane (GPTMS) in proportion 1:1 to form an organo functional silanes
group; hydrolysing the organo functional silanes group in an acid water having
atleast one phosphate based acid up to 1 wt. percent, the pH of the acid water
being maintained around 6-7; and stirring the said organo functional silanes group
making it homogenised, condensed, cross-linked.

In another aspect the invention provides a Poly-condensed silane having density
(201): 1.01-1.2 gm/cm3, boiling point: approx. 250°C, pH: 5-7 and solid content: 15
- 30%.
In still another aspect the invention provides a silane solution for coating, the silane
solution comprising a mixture of the above mentioned Poly-condensed silane (2-20%
by weight), a neutralizing agent (0.5-2% by wt), a flash rust inhibitor (0.2-2% by
wt), a chelating agent (0.25-3% by wt.), a flexibiliser (0.25-3% by wt.), a de-
foamer (0.25-2% by wt.), a levelling agent (upto 0.1% by wt.), a corrosion
resistance pigment(upto 0.2% by wt.), and water (rest) as a solvent.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 illustrates various steps of a process for making a poly-condensed silane in
accordance with an embodiment of the invention.
FIGS. 2a and 2b illustrate hydrolysis and crosslinking steps of the process for
making a poly-condensed silane in accordance with an embodiment of the invention.
FIGS. 3a-3d show salt spray picture of coated galvanised steel at different interval
in an experimental analysis in accordance with an embodiment of the invention.
FIGS. 4a-4d shows salt spray picture of coated galvannealed steel at different
interval in an experimental analysis in accordance with an embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the invention provide a method for making a Poly-
condensed silane, the method comprising steps of mixing amino propyl tri-methoxy
silane (AMEO) with 3-gycosidoxy propyl tri-methoxy silane (GPTMS) in proportion
1:1 to form an organo functional silanes group; hydrolysing the organo functional

silanes group in an acid water having atleast one phosphate based acid up to 1 wt.
percent, the pH of the acid water being maintained around 6-7; and stirring the said
organo functional silanes group making it homogenised, condensed, cross-linked.
Another embodiment of the invention provides a Poly-condensed silane having
density (20t;): 1.01-1.2 gm/cm3, boiling point: approx. 250°C, pH: 5-7 and solid
content: 15 - 30%.
Yet another embodiment of the invention provides a silane solution for coating, the
silane solution comprising a mixture of: a Poly-condensed silane (2-20% by weight),
the Poiy-condensed silane formed by a method comprising following steps: mixing
amino propyl tri-methoxy silane (AMEO) with 3-gycosidoxy propyl tri-methoxy silane
(GPTMS) in proportion 1:1 to form organo functional silanes group; hydrolysing the
organo functional silanes group in an acid water having atleast one phosphate based
acid up to 1 wt. percent, the pH of the acid water being maintained around 6-7; and
stirring the said organo functional silanes group making it homogenised, condensed
and cross-linked; a neutralizing agent {0.5-2% by wt.), a flash rust inhibitor (0.2-2%
by wt.), a chelating agent (0.25-3% by wt.), a flexibiliser (0.25-3% by wt.), a de-
foamer (0.25-2% by wt.), a levelling agent (upto 0.1% by wt.), a corrosion
resistance pigment(upto 0.2% by wt.), and water (rest) as a solvent.
Shown in FIG. 1 are various steps of a process (100) for making a Poly-condensed
silane via water-borne sol-gel solution technique.
At step (104), amino propyl tri-methoxy silane (AMEO) with 3-gycosidoxy propyl tri-
methoxy silane (GPTMS) is mixed in a proportion 1:1 to form an organo functional
silanes group.
At step (108), the organo functional silanes group is hydrolysed in water having
atleast one phosphate based acid up to 1 wt. percent (shown in FIG. 2a). The
phosphate based acid may be H3PO4, H4P2O7, H5P3O10, H6P4O13, H3P3O9, P4O10.The

hydrolysing is done in drop by drop manner by thistle funnel or similar kind of
arrangement.
pH of the acid water is maintained around 6-7. Ammonia or amine derivatives are
used for the adjustment of pH value of the acid water.
At step (112), the said organo functional silanes group is stirred so as to make it
homogenised, condensed and cross-linked. This provides a dense network structure
of coating for protection of the substrate from corrosion (shown in FIG. 2b).
The obtained Poly-condensed silane solution has following physical properties:
- Density (20°C): approx. 1.01-1.2 gm/ cm3
- Boiling point: approx. 2501
- pH-value: 5-7
- solid content: approx. 15-30% (by wt.)
The Poly-condensed silane via the process (100) can be used for making a silane
solution for coating. The solution is meant for coating a galvannealed (GA) or
galvanised (GI) steel substrate.
The silane solution comprises a mixture of the Poly-condensed silane (2-20% by
weight) as mentioned above in process (100), a neutralizing agent (0.5-2% by wt.),
a flash rust inhibitor (0.2-2% by wt.), a chelating agent (0.25-3% by wt.), a
flexibiliser (0.25-3% by wt.), a de-foamer (0.25-2% by wt.), a levelling agent (upto
0.1% by wt.), a corrosion resistance pigment (upto 0.2% by wt.) and water (rest) as
a solvent.
In an embodiment a drying solvent can also be used, optionally, for fast curing of
the coating. Drying solvent can be used upto 2% by wt. Isopropyl alcohol or ethanol
can be used as drying solvent.

Neutralizing agent: amine or its derivative is used as the neutralizing agent. The said
neutralizing agent maintains the pH-value of the coating composition in the range of
7 to 8. Sodium hydroxide can be used as one of the neutralizing agent.
Flash rust inhibitor: the flash rust inhibitor is in the form of aqueous solution. 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 used as in an
embodiment of the invention include compounds such as sodium nitrite, nitrate salt,
heterocyclic azole and a mixture of one or 10-25% of zinc organo salts of branched
fatty acids, <2.5% of zinc salts of naphthenic acid, 10-25% morpholine benzoate (all
are in wt %).
The flash rust inhibitor used has the following physical properties:
Density (20oC): approx. 1.04 gm/ cm3
pH-value: 8-10
Chelating agents: The chelating agents are used to enhance the bond strength
between polymer and metal. The chelating agents include a bifunctional
organosilane having a reactive organic amino and a hydrolysable inorganic
phosphates functional group. The preferred examples of the chelating agent include,
but not limited to phosphates. One the example can be
hexamethoxymethylmelamine (HMMM)
Flexibiliser: In order to increase the flexibility of the coating, an additional additive
like polyester acrylate is added in the coating formulation. The preferred example of
the flexibiliser, but not limited to, is a reaction product of triethyl amine and n-ethyl-
2-pyrrolidone or Vinyl silane.
De-foamer: Fatty acid is used as de-foamer.
Levelling agent: Glycols is used as levelling agent.

Corrosion resistance pigment: The preferred examples of the corrosion resistance
pigments include nano zinc oxide, cerium salt, Zirconium salt, zinc phosphate
derivatives or any combination thereof.
Water (rest) as a solvent.
The coating on the steel substrate can be done by roll coating, dipping, brush
coating and spraying. In coating over the substrate, weight of the coat is not
pertinent rather; the coating can be applied in such a way that the final dry film
thickness is achieved in the range of 500nm to 10 micron. The coating is formulated
in such a manner that it can be applied through online continuous galvanising line
after galvanisation and it cures fast (up to 30 second) in infrared oven. The
temperature of the curing lies in between 32-120t. The temperature of curing of
coating can be lowered by addition of few additives like polyamine and polyimide
derivatives.
In accordance with an embodiment of the present invention, the unobvious effect of
anionic part of an acid used in the hydrolysis step of the sol-gel process on the
anticorrosive properties can be attributed to the use of Ortho-Phosphoric acid in
place of acetic acid.
Experimental Trials
The following examples should not be construed to limit the scope of invention.
Analysis of AGA (AMEO + GPTMS + Acetic acid) and AGP (AMEO + GPTMS +
Phosphate containing acid) coating solution as well as their coated samples is done
to characterize the effect of acid on final coating layer formed on galvanised and
galvannealed steel substrate. To characterize the corrosion resistance offered by the
coatings under accelerated corrosive environment continuous Salt Spray Test (SST)
was done.

Commercially available galvanized and galvannealed steel substrate was used as the
substrate for applying the coating of the present invention.

The coating formulation of example 1 when applied on galvanized and galvannealed
steel substrate provides uniform coating with 0.5 to 2 micron dry film thickness.
FIG. 3a shows the picture of the coating formulation provided for 72 hours SST life
for GI sample and FIG. 3b shows of the same sample after 172 hours SST life as
per ASTM B117 standard.
FIG. 4a shows the picture of the coating formulation provided for 400 hours SST life
on GA sample.


FIG. 3c shows the picture of the coating formulation provided for 72 hours SST life
for GI sample and FIG. 3d shows of the same sample after 172 hours SST life as
per ASTM B117 standard.
FIG. 4b shows the picture of the coating formulation provided for 400 hours SST life
for GA sample.
Advantages
The developed coating is a chrome free coating which has high corrosion resistance
and good adhesion property. The coating is an eco-friendly corrosion resistance
coating for steel substrate. Still the coating is an eco-friendly corrosion resistance
coating for steel substrate.

WE CLAIM:
1. A method for making a Poly-condensed silane, the method
comprising steps of:
mixing amino propyl tri-methoxy silane (AMEO) with 3- gycosidoxy
propyl tri-methoxy silane (GPTMS) in proportion 1:1 to form an
organo functional silanes group;
hydrolysing the organo functional silanes group in an acid water
having atleast one phosphate based acid up to 1 wt. percent, the
pH of the acid water being maintained around 6-7; and
stirring the said organo functional silanes group making it
homogenised, condensed, cross-linked.
2. The method as claimed in claim 1, wherein the hydrolyzing is done
in drop by drop process.
3. The method as claimed in claim 1, wherein pH of the acid water is
being adjusted by ammonia or amine derivative.
4. The Poly-condensed silane having density (20 oC): 1.01-1.2 gm/cm3
as claimed in anyone of the claims 1 to 3.
5. The Poly-condensed silane having boiling point: approx. 250°C as
claimed anyone in anyone of the claims 1 to 3.
6. The Poly-condensed silane having pH 5-7 as claimed in anyone of
the claims 1 to 3.
7. The Poly-condensed silane having solid content: 15 - 30% as
claimed in anyone of the claims 1 to 3.

8. A Poly-condensed silane having density (20 oC): 1.01-1.2 gm/cm3,
boiling point: approx. 250°C, pH: 5-7 and solid content: 15 - 30%.
9. A silane solution for coating, the silane solution comprising a
mixture of:
a Poly-condensed silane (2-20% by weight),
the Poly-condensed silane formed by a method comprising
following steps:
mixing amino propyl tri-methoxy silane (AMEO) with 3-gycosidoxy
propyl tri-methoxy silane (GPTMS) in proportion 1:1 to form
organo functional silanes group;
hydrolysing the organo functional silanes group in an acid water
having atleast one phosphate based acid up to 1 wt. percent, the
pH of the acid water being maintained around 6-7; and
stirring the said organo functional silanes group making it
homogenised, condensed and cross-linked;
a neutralizing agent (0.5-2% by wt.),
a flash rust inhibitor (0.2-2% by wt.),
a chelating agent (0.25-3% by wt.),
a flexibiliser (0.25-3% by wt),
a de-foamer (0.25-2% by wt.),

a levelling agent (upto 0.1% by wt.),
a corrosion resistance pigment(upto 0.2% by wt.), and
water (rest) as a solvent.
lO.The silane solution for coating as claimed in claim 9, wherein the
coating is performed on the GA and GI steel substrate.
11.The silane solution for coating as claimed in claim 9, wherein the
flash rust inhibitor is one of sodium nitrite, nitrate salt, heterocyclic
azole and a mixture of one or 10-25% of zinc organo salts of
branched fatty acids, <2.5% of zinc salts of naphthenic acid, 10-
25% morpholine benzoate.
12.The silane solution for coating as claimed in claim 9, wherein the
flash rust inhibitor has density (2011): approx. 1.04 gm/ cm3 pH-
value: 8-10.
13.The silane solution for coating as claimed in claim 9, wherein the
chelating agent is hexamethoxymethylmelamine (HMMM).
14.The siiane solution for coating as claimed in claim 9, wherein the
flexibiliser is Vinyl silane or a reaction product of triethyl amine and
n-ethyl-2-pyrrolidone.
15.The silane solution for coating the as claimed in claim 9, wherein
the de-foamer is fatty acids.
16.The silane solution for coating as claimed in claim 9, wherein the
leveling agent is glycols.

17.The silane solution for coating as claimed in claim 9, wherein the
corrosion resistance pigment is nano zinc oxide, cerium salt,
Zirconium salt, zinc phosphate derivatives or any combination
thereof.
18.The silane solution for coating as claimed in claim 9, wherein the
neutralizing agent is sodium hydroxide.