Field of the Invention
The present invention relates to a superhydrophobic anticorrosive
coating without fluoro compounds and inhibitive pigments and process
thereof. More particularly, the invention describes superhydrophobic (SHP)
coatings without the use of any low surface energy materials like fluorocompounds,
silanes and long chain fatty acids. The present invention
relates to SHP anticorrosive coating with micro/nano roughness without
any inhibitive pigment wherein the anticorrosive property is achieved
through the superhydrophobic nature i.e. water rolls off from the surface.
Background of the Invention
Superhydrophobicity is a distinctive characteristic of the surface,
implying extreme water repellency and have a contact angle over 150°.
Their characteristic water repellent property could be utilized by corrosion
preventive coatings to protect the metal substrate against corrosion.
Coatings are an effective way to prevent corrosion and coatings consist of
binder, pigments, additives and solvent. Corrosion resistant coatings
protect metal against degradation from moisture and industrial chemicals.
They act as a barrier between corrosive environment and metal. Corrosion
resistant coatings are broadly classified as barrier, inhibitive or sacrificial
depending on the type of pigments used. The efficiency of the coating
could be enhanced by improving the hydrophobicity of the coatings.
SHP coatings find widespread potential applications and gather
great interest due to their exotic, invoking properties like self-cleaning,
corrosion protection, anti-icing, anti-soiling, anti-fogging, antifouling and
ice-phobic coatings for airplane surfaces. Water droplets do not wet SHP
surfaces and they appear almost spherical because of the micro/nano
roughness that effectively entraps air, thereby decreasing solid-liquid
interface that in turn enhances hydrophobicity. Modifying the surface by
altering the morphology will alter the solid-liquid interface. The shape of
the water drop on a coating also depends on the surface free energy of the
polymeric coating. The contact angle achieved on the surface is the result
of balancing interfacial forces between solid i.e. substrate, liquid i.e. water
and air interfaces. The contact angle is maintained in such a way to
minimize the surface free energy of the coating as a whole.
SHP coating can be achieved in two ways, either by changing the
surface energy of the materials or by roughening the surface of the
coating. Introduction of fluorinated groups into the polymeric backbone will
reduce the surface energy because of high electronegativity and small
atomic radius of fluorine that enables the formation of a strong covalent
bond between fluorine and carbon. From a multitude of safety, health,
economic and environmental issues fluoropolymer would not be a safe
option. For example, perfluorooctanoic acid (PFOA) is carcinogenic.
Perfluorinated polyethers have poor weatherability and it is proposed that
it might be due to the photochemical attack on unprotected secondary
hydrogens at the alpha position relative to the non-fluorinated diol chain
ends. Also, fluoropolymer has the ability to bioaccumulate. SHP coating
could also be accomplished by tuning the morphology of the coating that
can be achieved using lithographic methods, template-based techniques,
plasma treatment, chemical deposition, layer-by-layer (LBL) deposition,
colloidal assembly, phase separation, and electrospinning.
Reference may be made to Kissel et.al., U.S Patent 2015/0030833
describes a process for preparing optically clear superhydrophobic coating
by hydrolyzing alkoxysilane precursor to form polysilicate with hydroxyl
groups which are functionalized by fluorosilanes.
Reference may be made to Weber et.al.,U.S Patent 2014/0287243
explainsmethod for preparing superhydrophobic coatings wherein the
coating comprises of fluoropolymer, fluorophilic silica particle and
fluorocarbon solvent. As per this invention, to achieve superhydrophobicity
70 weight % of fluoroalkyl modified silica nanoparticles is required, which
is a very high loading for nanoparticles.
Reference may be made to Gesfordet.al., U.S Patent
2014/0087134 discloses superhydrophobic coatings with low volatile
organic compound systems comprising polyurethane/polyester
urethane/polyacrylic urethane and/or polyurethane carbonate, siloxanes
and/or alky, haloalkyi, fluoroalkyl, perfluoroalkyi moieties and oxides of
metalloids/metals.
Reference may be made to Loth et.al.,U.S Patent 2014/0113144
discloses superhydrophobic nano composite coating composition
containing moisture cured polyurethane, a fluoropolymer, a nano filler and
an organic solvent. For obtaining superhydrophobicity along with good
adhesion a 1:1 weight ratio of polyurethane and fluoro polymer is required,
which is of high fluorine content. In addition to that, since it is moisture
cured polyurethane, baking at 100°C is necessary to cure the coating.
Reference may be made to Sunder et.al.,U.S Patent 2014/0208978
discloses superhydrophobic coating composition of a hydrophobic agent, a
binder, or an etching chemical. It was mentioned that the coating exhibits
superhydrophobicity after 30 minutes. Since, the etching chemicals like
sulphuric acid, phosphoric acid, etc., that could lead to corrosion.
Reference may be made to Kissellet.al., U.S Patent 2014/0134907
discloses durable polymer aerogel based superhydrophobic coatings
comprising of composite material. The coating consist of polysilicate
aerogel with surface functional groups derivatized with a silylating agent
dispersed in polymer comprising poly(methyl methacrylate), polystyrene,
poly(butyl methacrylate), poly(tert-butyl methacrylate), poly(methyl
acrylate), poly(butyl acrylate), poly(tert-butyl acrylate), poly(perfluorooctyl
methacrylate) and/or vinylpolymer.
Reference may be made to Simpson et.al.,U.S Patent
2012/0107581 discloses optically transparent superhydrophobic coating
comprising hydrophobic particles with an average particle size of 200 nm
or less, binders like ethyl cyanoacrylate, polyacrylic acid,
polytetrafuoroethylene; polyurethane and Fastrack TM XSR and solvents
like acetone, FluorinertTMFC-40 and propyl acetate. These coatings
transmit about 95% of incident light.
Reference may be made to Bleecheret.al.,U.S Patent
2012/0045954 discloses superhydrophobic, oleophobic and anti icing
coating. The coating composition comprise binder of
polyurethane/fluoropolymer/epoxy/thermoplastic powder coating, two
different sized particles where the first particles size ranges from 30 to 225
micrometer and the second particles size ranges from 1 nanometer to 25
micrometer.
Reference may be made to Gao et.al., U.S Patent 2011/0111656
discloses durable superhydrophobic coatings which comprise acrylic
polymer, polysiloxane oil, hydrophobic particles, metal oxides, solvents
and other additives. The coating consist of acrylic polymer 10 to 80 weight
%, polysiloxane oil 5 to 40 %, hydrophobic particles 1 to 50 weight %and
0.1 to 10 weight % of metal oxide.
Reference may be made to Ajayagosh et.al., U.S Patent
2010/0330277 discloses nanocomposite material fo rthe preparation
superhydrophobic coating. The coating comprises carbon nanotubes and
oligo (p-phenylenevinylene) solution in an organic solvent. Drop casted
nanocomposite solution exhibit superhydrophobicity where the weight ratio
of oligo (p-phenylenevinylene) to carbon nanotubes is in the range of 40-
60 %. Carbon nanotubes used were multiwalled with diameter range 110
to 170 nm.
Nonetheless, generally the techniques employed for the output of
superhydrophobic surfaces are expensive and/or not easily suited for
industrial scale use. It involves strict condition, expensive materials
(perfluoro compounds) and uneconomical procedures like etching, plasma
treatment, chemical vapour deposition and the use of templates.
Objectives of the Invention
The main objective of the present invention is to provide a method
to prepare superhydrophobic anticorrosive coatings without fluoro
compounds and inhibitive pigments in a cost effective manner without the
use of any low surface energy materials like fluoro-compounds, silanes,
long chain fatty acids and inhibitive pigments.
Another objective of the present invention is to engineer a SHP
coating with micro/nanoroughness.
Yet another objective of the present invention is to develop
superhydrophobic anticorrosive coating, comprising of a binder,
nanotitania and extender pigments such as nanosilica, magnesium silicate
and additives like aluminium stearate.etc.
Still another objective is to formulate a durable anticorrosive coating
without any inhibitor pigment.
Yet another objective of the present invention is to develop the
superhydrophobic anticorrosive coating system without any inhibitive
pigment exhibiting corrosion resistance even after 1000 hours of exposure
in salt spray environment ASTM B117.
Another objective of the present invention is to formulate a coating
that cures ina temperature range of 27±3 °C.
Another objective of the present invention is to provide a process
for the preparation of superhydrophobic anticorrosive coating free of fluoro
compounds.
The novelty of this invention is the development of non-fluorinated
superhydrophobic anticorrosive coatings without the use of any low
surface energy materials like fluoro-compounds, silanes and long chain
fatty acids. These SHP coatings are formulated without any inhibitive type
of pigments. The developed non-fluorinated superhydrophobic
anticorrosive coating without any inhibitive pigment has with stood upto
1000 hours of salt spray (ASTM B117). The novelty of this invention has
been achieved by inventive steps of preparing superhydrophobic
anticorrosive coating which comprises of binder, main pigments like nano
titania and extender pigments such as nanosilica, magnesium silicate and
additives like aluminium stearate,etc.
The foregoing summary and the detailed description of the
invention will be better understood when read in conjunction with the
appended figures.
Figure 1A, 1B, 1C shows the water contact angle of the coating
Figure 2A represents the SHP coating samples before and after
exposure to salt spray- ASTM B117
Figure 2B represents the commercial epoxy zinc phosphate coating
samples before and after exposure to salt spray - ASTM B117
Figure 3 represents a graph showingWater vapour transmission of
SHP coating - ASTM D1653
Figure 4A represents the FE-SEM image of the SHP coating
Figure 4B represents the EDAX line profile of the SHP coating
Accordingly, the present invention provides a superhydrophobic
anticorrosive coatings without fluoro compounds and inhibitive pigments
which comprises alkyl/aryl substituted silicone binder, aromatic
hydrocarbon like toluene, para - xylene, meta - xylene and ortho - xylene
as solvent and pigments of micron and nanosized like nanotitania (20 - 50
nm), nanosilica (20 - 50 nm); magnesium silicate and aluminium stearate
wherein superhydrophobicity and anticorrosive properties are achieved
without any low surface energy materials like fluoro-compounds, silanes
and long chain fatty acids and inhibitive pigments, respectively.
In an embodiment of the present invention, the addition of primary
and extender pigments are in powder form while blending with binder.
In another embodiment of the present invention, one of the
extender pigments should have an oil absorption value above 300 to 350
ml/100gram as per ASTM D1483. It should be noted that to achieve
superhydrophobicity along with a good tilting angle it has to be loaded
more than 60% in a total of 15 % pigment volume concentration (PVC)
In another embodiment of the present invention a process for manufacture of
superhydrophobic anticorrosive coating comprises;
a) homogenous 30-40% alkyl/aryl substituted silicone binder (Molecular
weight-165000 - 199000) solution was prepared by using aromatic
hydrocarbon which comprises toluene, para - xylene, meta - xylene and
ortho - xylene as a mixture or individually;
b) Premixed pigments like nanosilica, nanotitania (rutile), magnesiumsilicate
and aluminum stearate were added to that binder solution.
c) the binder, pigments and solvent were added, mixed and dispersed using
a high speed homogenizer for about 20 minutes;
d) the degree of dispersion was tested by Hegmann gauge and had a value
of 8 - 9 .
SHP coating is formulated with volume solids (VS) of 30 - 40 % and
pigment volume concentration (PVC) of 15%. The alkyl/aryl substituted
silicone binder of molecular weight ranging from165000 to 199000 is used.
Aromatic hydrocarbon which comprises toluene, para - xylene, meta -
xylene and ortho - xylene as a mixture or individually is used as the
solvent. This coating consists of both nano and micron sized pigments to
induce micro-nano roughness which is an essential factor to impart
superhydrophobicity. The pigments consist of nanotitania as main pigment
and the extender pigments like nanosilica, magnesium silicate and
aluminium stearate and atleast one of the pigments used should have an
oil absorption value of 300 to 350 ml/100gram. The particle size of the
nanotitania used here was in the range of 20 - 50 nm and nanosilica of
size 20 - 50 nm.
The variation in pigment composition is detailed below
A. Nanotitania 20 %, nanosilica 50% and remaining 30% consist of
magnesium silicate and aluminium stearate.
B. Nanotitania 10%, nanosilica 60% and remaining 30 % consist of
magnesium silicate and aluminium stearate.
C. Nanotitania 10%, nanosilica 70% and remaining 20 % consist of
magnesium silicate and aluminium stearate.
A homogenous 30-40% alkyl/aryl substituted silicone binder
(Molecular weight-165000 - 199000) solution was prepared by using
aromatic hydrocarbon which comprises toluene, para - xylene, meta -
xylene and ortho - xylene as a mixture or individually. Premixed pigments
like nanosilica, nanotitania (rutile), magnesiumsilicate and aluminum
stearate were added to that binder solution. The binder, pigments and
solvent were added, mixed and dispersed using a high speed
homogenizer for about 20 minutes. The degree of dispersion was tested
by Hegmann gauge and had a value of 8 - 9.Then it was stored in an
airtight container. It had been stirred well before application on steel
panels. The composition of the pigment used for preparing various
systems is given in the Tablel.
The composition and thickness of the SHP coating are as follows:
Binder : Silicone (M. wt165000-
199000)
Solvent : Xylene
Volume solids :30-40 %
Pigment Volume Concentration(PVC) : 15%
Dry film thickness : 70 - 80(am
S.No
1.
2.
3.
4.
Pigment
Nanotitania (Rutile)
Nanosilica
Magnesium silicate
Aluminium stearate
Quantity in %
System A
20
50
20
10
System B
10
60
20
10
System C
10
70
10
10
Table 1 Composition of the pigment or SHP coating
The following examples are intended as a way to illustrate the
invention in actual practice and are provided for exemplary purposes to
facilitate the understanding of the disclosure therefore should not be
construed to limit the scope of the present invention.
Example I
The mild steel panels of size 10 X15 cm and 10 cm X 10 cmwere
prepared as per ASTM G1/ ISO 8501 Sa 2.5 / Steel Structures Painting
Council (SSPC) SP2. The panels were cleaned with acetone and kept in
desiccator. The prepared coatingswere applied to the prepared mild steel
panels by air spray and dried/cured at 27±3 °C.The composition and
thickness of the SHP coating are as follows:
Binder
199000)
Solvent
Volume solids
Pigment Volume Concentration (PVC)
Dry film thickness
Silicone (M. wt165000-
Xylene
30 - 40 %
15%
70 - 80|im
S.No
1.
2.
3.
4.
Pigment
Nanotitania (Rutile)
Nanosilica
Magnesium silicate
Aluminium stearate
Quantity in %
10
60
20
10
Table 2 Composition of the pigment for SHP coating as in Example 1
Testing superhydrophobicity by Contact angle goniometer
Superhydrophobic nature of the coatings was tested by contact
angle goniometer (OCA 35 Data Physics) in static mode.The mild steel
panels of size 10 X15 cm were coated with SHP coatings System A,
System B and System C with a coating thickness of about 70- 80 pm.
Then it was air dried. The coated samples were mounted on the stage in
the instrument and a volume of 7pl of distilled water was placed and water
contact angle (WCA) was measured using Laplace - Young equation. The
tilting angle(TA) was measured by tilted drop method. The WCA and tilting
angles of the various systems are given in Table 3.
System
A.
B.
C.
Water contact angle (°)
123
152
161
Tilting angle (°)
40
20
15
Table3. Contact angle measurements for the prepared coating
System B and System C were showing superhydrophobicity (>150°),
whereas System A was not superhydrophobic (<150°). System C had
visuaMy observable cracks in the coatings. So, further tests were carried
out for System B alone.
Testing Micro/Nano roughness on the SHP coating by FESEM
analysis
The coated sample was cut into 1 cm X 1cm dimension. It was
sputtered with gold for conductivity and the topography of the sample was
imaged (Figure 4a). It showed micron sized sphere with nanoparticles on
its surface. The existence of micro/nano roughness on the substrate is
responsible for the superhydrophobic property since this scale of
roughness effectively entraps air. The roughness profile of the substrate
(Figure 4b) was analyzed by elemental analysis using energy dispersive
X-ray spectroscopy analysis in conjunction with line profile analysis.SHP
coating has micro/nano roughness and the micro roughness ranges from
10 to 20 micrometer and nanoroughness ranges from 100 to 200
nanometer.
Testing Corrosion Resistance of Coatings using salt spray
t h e corrosion resistance of the SHP coating was tested by the salt
spray test as per ASTM B117. In addition to the SHP coating, commercial
epoxy zinc phosphate primer of same thickness was evaluated as a
standard. The mild steel panels of size 10 X15 cm were coated with SHP
coating and commercial epoxy zinc phosphate paint with a coating
thickness of about 70- 80 |jm. The four sides of the panels were masked
with wax to avoid galvanic effect between the edges and the coated metal
surfaces. The panels were placed in 15 - 30° from vertical and parallel to
the direction of flow of fog in the chamber. The panels were closely
monitored by visual inspection. The SHP coating and commercial epoxy
zinc phosphate paint samples had passed 1000 hours of salt spray.
Testing Water Vapour Transmission of SHP coating
The permeability of the coating was tested as per ASTM D1653 for
the resin, superhydrophobiccoating and for comparative purpose on
hydrophobic paint.Free film was casted by coating the resin/paint on a
Teflon sheet and then removed after drying. They were then placed in
Payne cupfilled with water,placed in a desiccator and weighed
periodically.The change in weight was plotted against time
(Figure3).Water vapour transmission rate of the SHP coating was
calculated from the slope of the linear fit and the valueis8.64 gm"2h"1. It is
clear from the graph that the water vapour transmission rate of
superhydrophobiccoatingis low.
Testing the adhesion of the SHP coating to the substrate by pull off
strength
Adhesion of the SHP coating was tested as per ASTM D4541. The
mild steel panels of size 10 X15 cm were coated with a coating thickness
of about 70- 80 pm was fixed with dolly with flat conic base of 2 cm
diameter using epoxy adhesive and allowed it to cure for 7 days.After
curing, the dolly was removed by giving force using pull-off adhesion
tester. The dollies got detached from the coating at an applied force of
1MPa for all the steel panels.
Testing the impact flexibility of the SHP coating
Impact flexibilityof the SHP coating was tested as per ASTM D6905.
The mild steel panels of 10 X15 cm were coated with a coating thickness
of about 70- 80 pm. A standard weight (1.8 Kg) was indented from
different height and visually observed for damage in the coating. The
coatings withstand upto an applied force of 10.58 J.
Testing the flexibility of the SHP coating
Flexibility of the SHP coating was tested as per ASTM D522.The
mild steel panels of 10 X15 cm X0.08 cm were coated with a coating
thickness of about 70- 80 |jm. The panels were bent in the mandrel and
observed for cracks. Cracks were not observed within a region of 5mm.
The SHP coating had passed in flexibility test.
Testing Abrasion resistance of the SHP coating by Taber Abraser
Abrasion resistance of the SHP coating was tested as per ASTM
D4060.The mild steel panels of dimension 10 cm X 10 cm were coated
with a film thickness of 70-80 pm. Abrasion resistance was evaluated by
abrading the SHP coated substrate using a rotary rubbing action of
abrasive wheels (CS-10) attached to a pair of pivoted arms to which
auxiliary masses of about 500 g (per wheel) were attached. The sample
was mounted by using flange holders. The specimen was weighed and
then subjected to abrasion for 1000 cycles or until wear through the
coating was observed. The sample after subjected to abrasion test was
weighed. The change in weight in milligrams per 1000 cycles was
recorded as wear index. The wear index of this superhydrophobic coating
is 0.3452 mg.
Oil absorption of pigment
Oil absorption of the pigments used in table 2 was evaluated as per
ASTM D1483 Gardner and Coleman method. This test method was used
to gather information about binder demand by the pigment. Linseed oil of
specific gravity 0.93 and acid value 3 ± 1 was used for this test method.
Here, linseed oil was added in drops from the burette to the pigment and
gently stirred. End point was fixed when the pigment forms a single ball. It
was expressed in grams of oil required for 100 gram of pigment. It was
done in duplicates and oil absorption value of nanosilica was 300 to 350
gram of oil per 100 gram of nanosilica, nanotitania was 0.4 to 0.6 gram of
oil per 100 gram of nanotitania, talc was 2 to 3 gram of oil per 100 gram of
talc and aluminium stearate was 1 to 2 gram of oil per 100 gram of
aluminium stearate.
The overall test results obtained for the SHP coating (of
composition given in table 2) as per ASTM were given in table 4.
S.No.
1
2
3
4
5
6
7
8
9
10
11
12
Physical Property
Degree of
dispersion
Drying time
Density
Viscosity
Dry film thickness
Salt spray
Water vapour
transmission
Adhesion
Impact test
Flexibility
Abrasion index
Oil absorption
ASTMNo.
D1210
D5895
D1475
D2196
D7091
B117
D1653
D4541
D2794
D522
D4060
D1483
Results for SHP coating
8 - 9
20 minutes
1.09 g/cc
920-930 cP
70 - 80 urn
Passed upto 1000 hours
8.64 gm"2h-1
1 MPa
Passed upto 10.58 J
Passed - No crack was observed upto 5
mm
0.3452
Nanosilica - 300 to 350 gram of oil per
value 100 gram of nanosilica,
Nanotitania - 0.4 to 0.6 gram of oil per
100 gram of nanotitania,
Magnesium silicate - 2 to 3 gram of oil
per 100 gram of magnesium silicate
Aluminium stearate - 1 to 2 gram of oil
per 100 gram of aluminium stearate
Table4.Physical properties of the SHP coating
Example II
The binder, solvent, volume solids and thickness of the coatings
were same as that in example I but the coatings was formulated without
any pigments. The coating was applied to panel of size 10 X15 cm and 10
cm X 10 cmwere allowed to cure at 27±3°C and the physical properties of
the coating were evaluated and the results were tabulated in the table 5.
The water contact angle and the tilting angle of the coating were carried
out as described in example I and the values were 93° and 40°,
respectively.
Binder : Silicone (M. wt165000-199000)
Solvent
Volume solids
Pigment Volume Concentration (PVC)
Dry film thickness
Xylene
30 - 40 %
0%
70 - 8G|am
S.No.
1
2
3
4
Physical Property
Degree of
dispersion
Drying time
Density
Viscosity
ASTM No.
D1210
D5895
D1475
D2196
Results for coating
8 - 9
20 minutes
1.10 g/cc
280 - 290 cP
10
15
5
6
7
8
9
10
11
Dry film thickness
Salt spray
Water vapour
transmission
Adhesion
Impact test
Flexibility
Abrasion index
D7091
B117
D1653
D4541
D2794
D522
D4060
70 - 80 urn
Passed upto24 hours
g^gm^n"1
1 MPa
Passed upto 10.58 J
Passed - No crack was observed upto5
mm
0.3577
Table 5. Physical properties of the coating
Example III
The binder, solvent, volume solids and thickness of the coatings
were same as that in example I but the coatings was formulated with
micron sized pigments.The coating wasapplied to panel of size 10 X15 cm
and 10 cm X 10 cmwere allowed to cure at 27±3 °C.The composition of
the hydrophobic paint is given below. The various properties of the
hydrophobic paint are as follows:
Binder
199000)
Solvent
Volume solids
Pigment Volume Concentration (PVC)
Dry film thickness
Silicone (M wt: 165000-
Xylene
30 - 40 %
15%
70 - 80(am
S.No
1..
2.
3.
Pigment
Titania (Rutile)
Magnesium silicate
Aluminium stearate
Quantity in %
45
45
10
PQ D E L H I . 1 1 - 0 1 - 2 . 8 1 7 1 7 ' • 8 7 ,
Table 6 Composition of the hydrophobic paint
The physical properties of the coating and the oil absorption value
of the pigments used as in table 6 were evaluated and the results were
tabulated in the Table 7. The hydrophobic nature of the coating was
confirmed by the water contact angle measurements and the tilting angle
as described in example I and the values were 97° and 20°, respectively.
S.No.
1
2
3
4
5
6
7
8
9
10
11
12
Physical Property
Degree of
dispersion
Drying time
Density
Viscosity
Dry film thickness
Salt spray
Water vapour
transmission
Adhesion
Impact test
Flexibility
Abrasion index
Oil absorption
value
ASTM No.
D1210
D5895
D1475
D2196
D7091
B117
D1653
D4541
D2794
D522
D4060
D1483
Results for hydrophobic paint
8 - 9
20 minutes
1.13 g/cc
1020 -1040 cP
70 - 80 urn
Passed upto 500 hours
9.54 gm^h1
1 MPa
Passed upto 10.58 J
Passed - No crack was observed upto 5
mm
0.3374
Titania-30 to 35 gram of oil per 100
gram of titania
Magnesium silicate - 2 to 3 gram of oil
per 100 gram of magnesium silicate
Aluminium stearate - 1 to 2 gram of oil
per 100 gram of aluminium stearate
The main advantages of the present invention are:
i. SHP coating has been prepared without fluoro which would be
environmentally friendly, cost effective and safer to use.
ii. The SHP coating passes 1000 hours of salt spray without any
inhibitive pigment.
iii. Inhibitive pigments are not used in this SHP coating which makes it
more environmentally benign, since inhibitive pigments contains
toxic materials which will leach out in the due course. In addition to
that, life time of the coating depends on a) percentage of loading of
the inhibitive pigment in the coating and b) depends on the
aggressiveness of the environment. The prepared SHP coating is
free from these two limitations because the anticorrosive nature of
the SHP coating does not depend on these two factors.
iv. The prepared SHP coating has anticorrosive property without the
use of any inhibitive pigment wherein the anticorrosive property is
achieved through the superhydrophobic nature i.e. water rolls off
from the surface.
v. The coating has a water contact angle of 152° without the use of
any low surface energy materials like long chain fatty acids
andsilanes.
vi. The SHP coating cures at a temperature range of 27±3 °C.
vii. The developed SHP coating can be applied by conventional
painting techniques including spraying, roller coating, dip coating
and brushing.

We Claim,
1. A superhydrophobic anticorrosive coating without fluoro compounds
and inhibitive pigments comprises;
a) alkyl/aryl silicone binder (M wt: 165000 -199000),30 - 40 %,
b) aromatic hydrocarbon which comprises toluene, para - xylene,
meta - xylene and ortho - xylene as a mixture or individually,
c) nanotitania (rutile) in the range of 20 - 50 nm, TO - 20 %,
d) nanosilica in the range of 20 - 50 nm 50 - 70 %,
e) magnesium silicate, 10 - 20 % and
f) aluminium stearate,10 %.
2. The superhydrophobic anticorrosive coating as claimed in claim 1,
wherein one of the pigments used should have an oil absorption value
in the range of 300 to 350 gram of oil /100gramof pigment and should
be loaded more than 60% in a total of 15 % PVC.
3. The superhydrophobic anticorrosive coating as claimed in claim 1,
wherein superhydrophobic anticorrosive coating has the following
characteristics
Binder : Silicone (M wt: 165000 -199000)
Volume solids : 30 - 40 %
Pigment Volume Concentration (PVC) : 15 %
Dry film thickness : 70 - 80^im.
4. The superhydrophobic anticorrosive coating as claimed in claim 1,
wherein superhydrophobic anticorrosive coating has been obtained
without the use of any fluoro compounds.
5. The superhydrophobic anticorrosive coating as claimed in claim 1,
wherein superhydrophobic anticorrosive coating has been formulated
without using any low surface energy materials like silanes and long
chain fatty acids.
6. The superhydrophobic anticorrosive coating as claimed in claim 1,
wherein superhydrophobic anticorrosive coating has been engineered
with micro/nano roughness with a coating composition and the micro
roughness ranges from 10 to 20 micrometer and nanoroughness
ranges from 100 to 200 nanometer.
7. The superhydrophobic anticorrosive coating as claimed in claim 1,
wherein superhydrophobic anticorrosive coating has anticorrosive
property without the use of any inhibitive pigment wherein the
anticorrosive property is achieved through the superhydrophobic nature
i.e. water rolls off from the surface.
8. The superhydrophobic anticorrosive coating as claimed in claim 1,
wherein superhydrophobic anticorrosive coating cures at a temperature
range of 27±3°C.
9. A process for manufacture of superhydrophobic anticorrosive coating
as claimed in claim 1 comprises;
a) homogenous 30-40% alkyl/aryl substituted silicone binder
(Molecular weight-165000 - 199000) solution was prepared by
using aromatic hydrocarbon which comprises toluene, para -
xylene, meta - xylene and ortho - xylene as a mixture or
individually;
b) Premixed pigments like nanosilica, nanotitania (rutile), magnesium
silicate and aluminum stearate were added to that binder solution.
c) the binder, pigments and solvent were added, mixed and dispersed
using a high speed homogenizer for about 20 minutes;
d) the degree of dispersion was tested by Hegmann gauge and had a
value of 8 - 9.