FIELD OF THE INVENION
The present invention relates to a water based Thin Organic Coating formulation
for galvanized materials.
BACKGROUND OF THE INVENTION
Thin Organic Coating' (TOC), also known as Organic Composite Coating, is a
polymer based coating formulation which comprises water based polymers,
corrosion inhibitors and other functional additives. A TOC formulation is
described in prior art for example, Indian Application No.430/KOL/2005. It
contained water based acrylic resin, polyurethane resin, chromate compound,
colloidal silica and Polyethylene wax. The low pot life is the major drawback of
this formulation; increase with time and becomes viscous gel in 48-96 hours.
Hence, it must be applied before the gel formation. The study revealed that
water soluble chromium compound is not compatible with polyurethane
dispersion resin. Therefore, the pot life decreases with the increase in
polyurethane resin percentage in coating formulation
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a water based Thin Organic
Coating formulation for galvanized materials.

Another object of the invention is to propose to propose a water based Thin
Organic Coating formulation for galvanized materials which is a corrosion
resistance, acrylic resin based coating formulation without polyurethane.
DETAILED DESCRIPTION OF THE INVENTION
A TOC coating solution was prepared without polyurethane, as given in Table 1,
named mere as base formulation. Different concentration of polyurethane
dispersion (PU) was added in the base formulation and coating solutions were
kept in closed condition at ambient temperature. The stability of coating
solutions was studied by viscosity measurement at different time interval. The
solution was rejected as failed when it became gel. The viscosity study result is
given in Table 2.



therefore, it was concluded that the PU is not compatible with the base
formulation. Also, higher the concentration of the PU, results in faster thickening
of formulation with time.
Step II
Two approaches were tried out to overcome the lower pot life observed in Table
2. First, different types of stabilizers were tried out for solution stability. Second,
the aqueous urethane-acrylic hybrid dispersions were used in place of physical
blending of the acrylic and polyurethane mentioned in prior art.
First, four types of stabilizer were selected and their different ratio was used in
. formulation. The stabilizers are:
1. DETA (Amine based) Diethylene triamine
2. 2-Ethoxy ethanol (alcohol based)
3. Mercapto ethanol (alcohol based)
4. Butoxy diglycol (ether based)

Four types of formulations were made by using above stabilizers and their
viscosity measured at different time interval, as given in Table 3. The stabilizer
concentration was varied from 0.5 to 1% in base formulation.
Table 3: Study the role of stabilizer on coating stability.

It was observed that the stability of coating solution was not improved by Ethoxy
ethanol and Butoxyglycol. Other two stabilizers, Diethylene Triamine and 2
Mercapto ethanol, were changed the colour of the base formulation from yellow
to brown which indicated that these stabilizers are not compatible with the base
formulation.
A second approach was to use the aqueous urethane-acrylic hybrid dispersion in
place of acrylic and polyurethane dispersion separately. The urethane-acrylic

hybrid dispersion combines the performance of urethanes (toughness, abrasion
resistance, flexibility) with those of acrylic (weatherability, hardness and
pigmentability). The physical properties of urethane-acrylic hybrid dispersion are
given in Table 4.
The coating solution prepared by using two types of urethane-acrylic hybrid
dispersion and their performance were studied by viscosity measurements and
physical observation at different time interval, as given in Table 5.


From above study, it is seen that the above formulation is also not stable.
Therefore, the coating formulation was considered for preparation without
polyurethane.
Prior art reveals that amino hydroxyl compounds are additives for water based
acrylic polymer with multifunctional properties. We selected 2-amino-2-methyl-
1-propanol (AMP) because it gives pot life stability, corrosion inhibitor effect,
wetting action, and adhesion. Also, the 1% solution of AMP has pH around 11.6
which is favourable for pH adjustment of coating formulation.
Again, the base formulation prepared as per Table 1 and then AMP added in
different concentration. The coating solution viscosity measured up to 6 months
which showed stable pot life in Table 6. The developed coating performance was
studied on galvanized steel sheet samples where a dry film thickness in range of
lto 2 urn was applied by dip process. The corrosion resistance performance of
the samples was evaluated by salt spray test (as per ASTM B117). We observed
that the white rust formation was increased by addition of AMP in the base
formulation, as given in Table 6.The 10 % white rust formation on galvanized
surface is considered as failure of the samples. The various constituents of the
thin organic coating in 100 parts by weight of the coating formulation comprises
40-60 parts of styrene acrylic resin, 0. 2 to 1 parts of chromium from any of a
water soluble chromium compound, 1 to 3 parts of 2-amino 2-methyl 1-propanol
(AMP) and 1 to 6 parts of Polyethylene wax. Rest being water. Chromium
content is selected from the water soluble chromium compound such as

ammonium dichromate, potassium dichromate, and sodium dichromate. The
coating formulation may further comprise of functional constituents such as nano
zinc oxide, colloidal silica, colouring agent, wetting agent, deformers, wherein
the total concentration of the functional constituents is up to 2 parts per 100
parts of the TOC formulation
Table 6: Water based coating formulation and its properties

Therefore, the formulation developed ads per the present invention, contained
AMP as a necessary constituents of coating formulation. The AMP addition should
be such that the final formulation pH should not greater than 9.0. Table 6
showed that the formulations were stable after 7000 hours by viscosity result.
The small viscosity increase (< 1 mPa.S ) might be due to evaporation of water
or instrument error limit. In table 6, the salt spray test result showed an increase
in corrosion resistance of the samples by addition of AMP.

WE CLAIM :
1. A coating formulation for galvanized materials, 100 parts by weight of the
coating formulation comprises:
40-60 parts of styrene acrylic resin;
0. 2 to 1 parts of chromium from any of a water soluble chromium
compound;
1 to 3 parts of 2-amino 2-methyl 1-propanol (AMP);
1 to 6 parts of Polyethylene wax; and
rest being water.
2. The coating formulation as claimed in claim 1, wherein the formulation
comprises of non volatile content in the range of 20 to 40 % at room
temperature.
3. The coating formulation as claimed in claim 1, wherein the formulation has a
pH 7 to 9 and specific gravity 1.0 to 1.05 g/cm3.
4. The coating formulation as claimed in claim 1, wherein the styrene acrylic
resin comprises of 40 to 50 % non volatile content by weight, pH 7 to 9.0
with particle size 0.05 to 0.5pm and specific gravity 1.01 to 1.1 g/cm3.

5. The coating formulation as claimed in claim 1, wherein 0.2 to 1 parts of
chromium content is selected from the water soluble chromium compound
such as ammonium dichromate, potassium dichromate, and sodium
dichromate.
6. The coating formulation as claimed in claim 1, wherein 1 to 6 parts of the
polyethylene wax is having 30 to 40% non-volatile content, pH 5-10.
7. The coating formulation as claimed in claim 1 further comprises functional
constituents such as nano zinc oxide, colloidal silica, colouring agent, wetting
agent, deformers, wherein the total concentration of the functional constituents
is up to 2 parts per 100 parts of the TOC formulation.
8. The coating formulation as claimed in claim 1, wherein the formulation has
viscosity in the range of 4 to 40 mPa.s at 25 °C.

ABSTRACT

The invention relates to a coating formulation where 100 parts by weight
formulation constitutes from (a) 40-60 parts of styrene acrylic resin (b) 0. 2 to 1
parts chromium from any of water soluble chromium compound (c) 1 to 3 parts
of 2-amino 2-methyl 1-propanol (AMP) (d) 1-6 parts of Polyethylene wax and (e)
rest water, the property of resultant coating formulation at room temperature
being is 20 to 40 % non volatile content by weight, 7 to 9 pH and specific gravity
1.0 to 1.05 g/cm3.