FIELD OF THE INVENTION;
This invention relates to a thin organic coating (TOC) for galvanized
wires, and a process for the preparation thereof.
This invention further relates to a thin organic coating for galvanised
wires and a process for the application thereof on galvanized wires in a
continuous wire galvanizing plant. The thin organic coating is water
based coating which improves the corrosion resistance performance,
lubricity, antifinger resistance, paint adhesion. The thin organic coated
galvanized wire can be used in many applications like fencing, farming,
poultry, field enclosures etc.
BACKGROUND OF THE INVENTION;
Galvanised wires are commercially produced by hot-dip zinc coating to
improve the corrosion resistance of steel wires by barrier and galvanic
action of zinc coating. When a galvanised product is exposed to the
natural atmosphere, many corrosion cells are formed on the surface and
thereby corrosion products are generally formed. The effective corrosion
products are Zn (OH2) and basic zinc salts. Basic zinc salts are formed in
atmospheres characterized by species such as CO2, NaCl and SOx. That
is, 2ZnC03.3Zn(OH)2 in mild atmosphere, ZnCl2.4Zn(OH)2 and

ZnCl2.6Zn(OH)2 in chloride atmosphere and ZnS04.4Zn(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 galvanized (GI) wire is
to increase the zinc coating weight. However, this increases the product
cost as zinc is a costly metal. Another, approach is to apply a chromate
passivation on galvanized wire but this makes only a little improvement
on coating lie. Furthermore, the painting of GI wire certainly improves
the service life but it requires a separate paint application facility and
also there is a high chance of paint peel off during the barbing operation.
OBJECTS OF THE INVENTION;
It is therefore an object of this invention to propose a thin organic coating
for galvanized wires, which is simple, easy to produce and cost-effective.
It is a further object of this invention to propose a thin organic coating
for galvanized wires, which imparts corrosion resistance, paint adhesion,
lubrication, anti fingerprint properly to the coated wires.
-3-
Another object of this invention to propose a thin organic coating for
galvanized wires, which allows them a practical level of grounding and
weldability to the GI wires.
These and other objects of the invention will be apparent from the
ensuing description when read in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS;
Figure 1 shows a schematic line diagram for Thin Organic Coating
application on GI wire in continuous galvanizing line.
DESCRIPTION OF THE DESCRIPTION;
This invention relates to a thin organic coating (TOC) for galvanized wires
and a process for the preparation thereof.
In accordance with this invention, the water based TOC formulation
comprises
a) styrene acrylic copolymer
b) polyurethane resin
c) chromate solution

d) polyethylene wax
e) surface active agents
Commercial grade styrene acrylic emulsion is used for the formulation.
The typical properties of the commercially available styrene acrylic
emulsion are: 35-50 wt% solid, pH 7.0-9.0, particle size 0.05-0.5 µm, sp.
Gr. 1.01-1.2, and white milky appearance. This styrene acrylic emulsion
is dissolved in water under high stirring condition to make 30-40 wt%,
preferably 30 wt% solid content and then filtered with 300|im filter cloth.
The styrene acrylic polymer is used in a proportion of 50 to 60 parts by
volume.
Commercial grade polyurethane dispersion is used for the above
formulation. 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:20-40 wt% solid, pH 8 to 10, viscosity 50-500 cps, particle
size 0.150 µm, anionic particle charge, TEA neutralizing amine, white
milky appearance. This polyurethane dispersion is dissolved in water
under stirring condition to make 20-40%, preferably 25% solid content

and then filtered it by 300 µm filter cloth. The polyurethane resin
dispersion is used in a proportion of 15 to 30 parts by volume.
The typical properties of polyethylene wax emulsion used in this
formulation is a white translucent non-ionic emulsion having 15 to 40
preferably 34-36% solid content, pH 7 to 10 with typical particle size of
0.6 microns. The Drop point of the wax components 138°C and hardness
of wax dmm is 0.5 max.
Commercial grade ammonium dichromate is used in this formulation.
The chromate solution is formulated by dissolving 900-1200 gm of
ammonium dichromate in 6 litre of deionised water and then adding
250-350 gm of sodium hydroxide to get pH of 6.5-8.5. The chromate
solution contains 150-200 gm per litres of ammonium dichromate in
water. The other chromium compound such as sodium, dichromate,
potassium dichromate can also be used to make soluble chromiumn
solution.
Chromate is used in 4 to 8 parts by volume of the composition. Additives
such as surface active agents are added to the formulation as per

requirement. The additives may be conventional antifoaming agents,
flash rust inhabitants, colouring agents, biocides etc.
The Thin Organic Coating is made by adding the following ingredients in
the sequence mentioned below.
a) 50 to 60 parts by volume of styrene acrylic copolymer
b) 15 to 30 parts by volume of polyurethane resin dispersion,
c) 4 to 8 parts of chromate solution
d) 0.5 to 10 parts of polyethylene wax
e) optional additives in the range of 0.1 to 5.0% by volume.
The optional additives ingredients are added in the above sequence and
mixed for above about 1 hour and then filtered with a 300 µm filter cloth.
The optional additives are antifoaming agents, biocides, colourants and
flash rust inhibitors.
The antifoaming agents are selected from propylene glycol myristate,
tetramethyl decynediol, tributoxyethyl phosphate, dimethyl hexylnediol,
polysiloxane polyether copolymer and their combination at a usage level
of 0.05-2%.

The colourant is selected from phenyl diisodecyl phosphite, lead
phosphite dibasic, calcium-zinc-molybdenum complex, pigment yellow
53, ultramarine blue and their combination at a usage level of 0.5-5%.
The flash rust inhibitors are selected from 2-aminomethoxy propanol,
basic ammonium benzoate, barium salt of dodecylnaphthalenesulfonic
acid, calcium salt of dodecylnaphthalenesulfonic acid, organic zinc
complex, amine-neutralized {2-mercaptobenzothiazolyl) thiosuccinic acid
and their combination at a usage level of 0.1-3%.
The biocides are selected from 5-chloro-2-methyl-isothiazoline-3-one, 2-
methyl-isothiazoline-3-one, 1,2-benzisothiazoline-3-one,sodium
hydroxymethylglycinate, tributyltin salicylate and their combination at a
usage level of 0.15-2.0%.
In an embodiment according to the invention, the formulation is applied
on galvanized wire in commercial continuous galvanized- line by dip
coating process followed by drying by radiant heater. The schematic line
diagram given in Figure 1 describes the TOC application process used for
coating GI wire in continuous galvanizing line for a single wire. The same

process can be simultaneously applies for multiples wires for higher
productivity.
The TOC formulation is applied on wires (1) in a continuous galvanizing
line, whereby galvanized wire exiting galvanizing bath (2), is quenched (3)
and led through a TOC bath (4). The application of the TOC composition
takes place either by dip, spray or roller or any other suitable coating
means. The coated wire may be passed through a suitable wiper (5), to
control the thickness of the film, and the wet film subsequently dried in a
drying oven (6), such as radiant heater/hot air oven/infrared oven which
is at a temperature of 300-700°. The wire is passed their oven at a high
speed, so that it resides in the oven for a maximum of 0.5-5 sec, and
attain a peak metal temperature of 60-200°C. The dry film thickness of
the TOC film on GI wire is 0.5 to 3.0 µm, which corresponds to a coating
weight of 560 to 3500 mg/sq m.
The dry, coated wires are then recoiled on drum (7).
The invention will not be explained in greater detail with the help of the
following non-limiting example:

EXAMPLE;
The TOC formulation was made using commercially available
constituents as follows:
The constituents (a) - (d) were mixed sequence mentioned below, under
high stirring for eight hours and then filtered with a 300 µm filter cloth.
a) 65 parts by volume of styrene acrylic copolymer at 30% solid
concentration
b) 25 parts by volume of polyurethane resin at 25% solid
concentration
c) 2 parts by volume of polyethylene wax at 34% solid cone;
d) 5 parts by volume of chromate solution
e) Other surface active agent used to further tailor made the
formulation as per the requirements such as the antifoaming
agent, flash rust inhibitors, colouring agent, biocides etc. They are
used either in single or in combination with other surface active
agents.
The TOC formulation enhances the life of galvanized surface. It provides

a dry film thickness of 1 to 3 µm with excellent corrosion resistance,
paint adhesion, lubrication, anti-fingerprints properties and allows a
practical level of grounding and weldability on GI wires.
The colour can also be development by using suitable pigment in coating
formulation.
WE CLAIM;
1. In a water based thin organic coating composition comprising
a) 50 to 60 parts by volume, of a styrene acrylic copolymer
b) 15 to 30 parts by volume, of a polyurethane resin
c) 4 to 8 parts by volume, of a chromate solution
d) 0.5 to 10 parts by volume, of a polyethylene wax and
e) optional additives.
2. The composition as claimed in claim 1, wherein said styrene
acrylic polymer emulsion having a solid content of 30-50 wt% is
used.
3. The composition as claimed in claim 1, wherein said
polyurethane resin dispersion having a solids content of 20-40
wt% is used.
4. The composition as claimed in claim 1, wherein polyethylene
wax emulsion having 15 to 40% solid content, pH 7 to 10, is
used.

5. The composition as claimed in claim 1, wherein chromate
solution is formed using a chromate salt such as ammonium
dichromate, potassium dichromate or sodium dichromate.
6. The composition as claimed in claim 1,5, wherein the chromate
solution has a pH of 6,5 to 8.5 and a concentration of 150 to
200 gms/L of the salt in water.
7. The composition as claimed in claim 1, wherein the additives
are conventional additives such as antifoaming agents, flash
rust inhibitors, colouring agents, biocides etc.
8. The composition as claimed in one of preceding claims, wherein
the antifoaming agents are selected- from propylene glycol
myristate, tetramethyl decynediol, tributoxyethyl phosphate,
dimethyl hexylnediol, polysiloxane polyether copolymer and
their combination at a usage level of 0.05-2%.
9. The composition as claimed in one of preceding claims, wherein
the colourant is selected from phenyl diisodecyl phosphite, lead
phosphite dibasic, calcium-zinc-molybdenum complex, pigment

yellow 53, ultramarine blue and their combination at a usage
level of 0.5-5%.
10. The composition as claimed in one of preceding claims, wherein
the flash rust inhibitors are selected from 2-aminomethoxy
propanol, basic ammonium benzoate, barium salt of
dodecylnaphthalenesulfonic acid, calcium salt of
dodecylnaphthalenesulfonic acid, organic zinc complex,amine-
neutralized (2-mercaptobenzothiazolyl) thiosuccinic acid and
their combination at a usage level of 0.1-3%.
11. The composition as claimed in one of preceding claims, wherein
the biocides are selected from 5-chloro-2-methyl-isothiazoline-
3-one,2-methyl-isothiazoline-3-one, 1,2-benzisothiazoline-3-one,
sodium hydroxymethylglycinate,tributyltin salicylate and-their
combination at a usage level of 0.15-2.0%.
12. A process for the preparation of a thin organic coating
composition comprising mixing
a) 50 to 60 parts by volume of styrene acrylic copolymer
b) 15 to 30 parts by volume of polyurethane resin dispersion,

c) 4 to 8 parts of chromate solution
d) 0.5 to 10 parts of polyethylene wax
e) optional additives.
under high stirring and filtered to obtain the coating
composition.
13. The process as claimed in claim 12, wherein stirring is effected
for above about 1 hour and filtered using a 300µm filter cloth.
14. A process for coating a galvanized wire using the thin organic
coating composition comprising quenching the wire existing the
galvanized bath, passing the quenched wire through a bath
containing the thin organic coating to obtain the wire coated
with the TOC, drying the coated wire by attaining a peak metal
temperature of 60 to 200°C, to obtain the dry coated wire.
15. The process as claimed in claim 14, wherein the coated wire is
passed through a wiper to control the TOC film thickness before
drying.

16. A GI wire coated with a thin organic coating composition,
wherein the thickness of the coating is 0.5 to 3.0pm
corresponding to a dry coating weight of 560 to 3500 mg per sq
meter.

In a water based thin organic coating composition comprising
a) 50 to 60 parts by volume, of a styrene acrylic copolymer
b) 15 to 30 parts by volume, of a polyurethane resin
c) 4 to 8 parts by volume, of a chromate solution
d) 0.5 to 10 parts by volume, of a polyethylene wax and
e) optional additives.