FIELD OF INVENTION
This invention generally relates to preparation of nano-microcapsule. This
invention further relates to a process of preparation of corrosion resistance self
healing thin organic coating on steel substrate.
BACKGROUND OF THE INVENTION
It is known in the art that self-healing constitutes one of the examples of smart
coating. When coatings develop cracks induced by application of mechanical,
thermal and chemical means, the integrity of the structure significantly weakens.
Since, internal cracks a deep inside material are difficult to detect and repair in
particular, the material normally possess an in-built self repairing properties
which can be stimulated by physical, chemical, mechanical or thermal means,
and which trigger the healing process. Such an observation and findings being
have now opened an age of new intelligent materials. Continuous efforts are
being made to mimic natural materials and to integrate self-repairing capability
into polymers and polymer composites. But these bioinspired approaches are not
completely a mimicry of biological processes because in many cases they are
clearly too complex. Therefore, a self-healing properties in the coating should
better be considered as bio-inspired rather than a bio-mimetic approach. Like
pharmaceutical industry microcapsule techniques is being used in corrosion
prevention coatings. Healing is achieved by incorporating healing agents and a
catalytic chemical triggers within a polymer matrix. When coating is damaged by
mishandling or misuse of the coated structure, micro capsules rupture and active
healing agent come out from the shell, and the catalyst heals the damaged area.
In short, self-healing material provides the following advantages over the
conventional coating :
i) Automatic repairing process
ii) Barrier protection of underlying substrates
iii) Auto-preservation of aesthetics of surface appearance of coatings, plastic
and films.
iv) Restoration of mechanical integrity of load bearing materials as in
composites.
The coated or entrapped materials are usually an active liquid but can be solid or
gas as well. This material is called core material. Likewise the coating materials
are known as capsule or shell.
The core of micro capsules is the mass to be encapsulated. The first step in
encapsulation process is the selection of the core material, depending upon the
end application and required functional properties. The coating materials should
have following properties:
1. Easily encapsulatable
2. Remain stable and reactive over the service life of a polymeric
coating at different environmental conditions.
3. Non-reactive with material to be encapsulated both during
processing and on prolonged storage.
4. Ability to seal and hold the storage materials.
5. Ability to provide maximum protection to the active material against
environmental conditions.
Microcapsules offer superior functions compared to non-capsulation applications.
The shell of the capsule protects the active ingredients (it contains i.e. 3 core
material), decrease the evaporation or transfer rate of the core materials and
one of the best method is to release the core materials at the time of
requirement only. Most of the core materials are toxic and hazardous in nature
and after being microcapsuled it is easy to handle such types of chemicals in
safer manner.
Core materials of microcapsules can be released by several mechanism, some of
them are outlined here.
1. Application of compressive/shear force can break down the microcapsule
and release the core material.
2. At high temperature the wall may melt down and releases the core
materials.
3. The core diffuses through the wall at a slow rate due to the influence of
an exterior fluid such as water or by some osmotic pressure.
To improve coatings by the known process of addition of additives involves only
improving the application of the coating to a substrate, not the ability of the
coating to repair itself upon its compromise.
Unless right chemistry is used to fabricate the microcapsule and its contents, it
may be found unsuitable before the coating is even applied, or at the time of
mixing. Again, unless the microcapsules is compatible with both its active
ingredients, polymer resin and solvent used for coating application, life of the
applied coating may be less than the desirable period.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a process to prepare
a microcapsule which can provide self healing ability in a polymeric network.
Another object of this invention to propose a process to prepare a fine nano size
microcapsule.
A further object of this invention to propose to prepare a self healing coating
composition which is resistant to saline atmosphere with high corrosion
resistance properties.
These and other objects of the invention will be apparent to a reader on reading,
the ensuring description in conjunction with the accompanying drawings.
SUMMARY OF THE INVENTION
A process for preparing at least one microcapsule to provide self-healing
properties to corrosion-resistant coating compositions, comprising the steps of:
mixing in a container deionized water and polyvinyl alcohol of 5 wt% at room
temperature under continuous mechanical stirring :mode; dissolving in said
mixture urea, ammonium chloride, and resorcinol; adding core chemical to the
solution including drop-wise addition of IN NaoH to maintain pH value between
2.0 to 4.0 applying an ultrasonic homoniser to the solution under continuous
mixing mode at room temperature at specified intensity; obtaining a 1:1.9 molar
ratio of formaldehyde to urea by adding formaline; heating the obtained
emulsion at a rate of l°C/m upto about 55°C; switching off the stirrer and the
heater after about 4-hours of continuous agitation at 800-2000 rpm; separating
under vacuum the suspension of microcapsules after ambient cooling of the
suspension; rinsing the microcapsules with deionized water and air-drying for
about 48 hours.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows the SEM morphology of microcapsules
Figure 2 - shows the DSC curve of Microcapsules
Figure 3 - shows the TG/DTA curve of microcapsules
Figure 4 - shows the FTIR graph of microcapsule in different
environment
Figure 4(a) FTIR spectra of microcapsule and core chemical
Figure 4(b) FTIR spectra of microcapsule before and after
grinding.
DETAIL DESCRIPTION OF THE INVENTION
A preferred embodiment of the present invention provides a corrosion-resistant
self-healing coating composition and a process for preparation of micro capsules
providing self-healing properties in coating composition. According to the
invention, microcapsules in the form of microscopic spheres with a diameter of
100-800nm are synthesized. The synthesized microcapsules are fabricated with
different inhibitors or active reagents to provide the self healing properties. The
fabricated microcapsules are incorporated in different polymer matrix for the
preparation of corrosion resistance self healing coatings. When this self healing
coated steel is mechanically ruptured such as may occur upon damage by impact
or abrasion, the active ingredients or inhibitor present inside the capsule flow
into the damage areas forming thin films of corrosion protection.
EXAMPLE
Microcapsules were prepared by in-situ polymerization in an oil-in water
emulsion. At room temperature, 200ml of deionised water and 0.5-15ml of 5
wt% polyvinyl alcohol (PVA) were mixed in a container under continuous
mechanical stirring (rpm-400). 0.5-15g urea and 0.1-5g ammonium chloride and
0.1 - 5g resorcinol were dissolved in the solution. Then, 1.0-5g of core chemical
(modified isocyanides/phenolphthalein/methyl methacrylate etc.) was added to
the above solution. The pH was maintained in between 2.0 to 4.0 by drop wise
addition of IN NaOH. A tapered 3.2 mm tip sonicator horn of a 750W ultrasonic
homoniser was placed in the solution for 3m at 40% intensity with continuous
mixing at 800 rpm in room temperature. This sonication step changes the
emulsion from slightly cloudy to opaque white 12.67g formalin (37%
formaldehyde) was then added, to obtain a 1:1.9 molar ratio of formaldehyde to
urea. The emulsion was covered and heated at a rate of l°C/m up to 55°C. After
4 h of continuous agitation at 800-2000rpm, the mixture and hotplate were
switched off. Once cooled, to ambient temperature, the suspension of
microcapsules was separated under vacuum. The microcapsules were rinsed with
deionised water and air dried for about 48h.
According to this invention, there is further provided a corrosion-resistant self
healing thin organic coating composition applicable on steel substrate. This
composition consists of:
a self healing coating formulation prepared from an emulsion of methyl hydrogen
seilicon; a microcapsule; a flash rust inhibitor; dispersing agent; and a nano
pigment. The detail formulation is given below :-
EXAMPLE
The methyl hydrogen silicon resin emulsion is used for preparing corrosion
resistant self healing thin organic coatings.
The adhesion promoter is selected from compounds such as silicon modified
acrylic resin and/or silicon modified derivative.
The flash rust inhibitors are selected from compounds such as sodium nitrite,
benzotriazole, a mixture of several inhibitors, whose composition is as follows :
110-25% of C12-C14 (2-benzothiazolythio) succinic acid tert 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 nenzoate
The nano pigment is selected from zinc oxide, silica, alumina, cerium oxide of
any combination thereof and water used for all these processes is deminaralised
water.
Titanium precursor is selected from titanium isopropoxide and ethylene glycol
monoethyl ether.
The coupling agents are selected from [2-(3,4-epoxycyclohexyl) ethyl trimethoxy
Silane] and [N-Phenyl-3 aminopropyl trimethoxy Silane], 3-
mercaptopropyltrimthoxy silane and Methylhydrogenpolysiloxane
In applying the corrosion resistant self healing thin organic coatings
compositions of the invention to substrates, any of well-known coating methods
such as dipping, spraying, roll coating and brush coating may be employed.
Although the coating weight of the composition is not particularly limited, it is
usually coated so as to give a coating thickness of 2 to 1,00 micron, in particular
1 to 50 micron after drying.
A series of Charecterisation tests were carried out on the capsule prior to
embedding in the polymer matrix to access capsule morphology, physical
properties and stability. Shell wall integrity, aggregation and micro capsule size
were observed by scanning electron microscope (SEM).
CAPSULE SIZE ANALYSIS
Capsule size was analysed by SEM. The micro capsule size is in a wide range of
20 - 250 micrometer5 with out the application of ultrsonicator. By application of
ultrasonicator particle size of 3 mm, the microcapsule decreases extensively and
it is in the range of 200-800 nm. The reason for this is that the fluid flow away
from the stirrer blades, many larger microeddis exist, and many smaller micro
eddies exist in the vicinity of the blades, all of which result in a wide length scale.
The microcapsule size can be controlled by adjusting the agitation rate. A
2000rpm with 3mint ultrasonicator, the average diameter of the prepared
microcapsule has been found to be 200nm.
MICROCAPSULE SURFACE MORPHOLOGY
Figure l(a-d) shows the SEM morphology of microcapsule. The shape of
microcapsule is spherical and the surface of the microcapsule is rough and
scraggly. The protuberant nanoparticles can increase the surface area of the
microcapsules and enhance surface adhesion.
THERMAL RESISTANCE OF MICROCAPSULES
The thermal stability of microcapsules plays an important rote in their application
in self healing composite. Figure 2 shows a DSC diagram of microcapsule. One
endothermic peaks and two exothermic peaks appear in the DSC curve of
microcapsule. The endothermic peak at around 90°C is due to the evaporation of
water and free formaldehyde. As respect to the two exothermic peaks the first
one at about 213°C is due to the polymerization of core material, which is
triggered by urea-derivatives and gaseous products such as ammonium,
nanomethyamine and trimethylamine yielde by PUF shell material and self
condensation of core material. The second exothermic peak at around 260° may
be due to the continuous polymerization reaction of core material.
Figure 3 shows a TGA diagram of microcapsule with UF wall shell, weight loss
near 100°C is mainly due to the removal of entrapped residual water and the
elimination of free formaldehyde and the weight loss at temperature between
200-300°C is mainly due to the decomposition of the PUF shell wall. The residual
undergoes extensive fragmentation near 400°C/ basically the microcapsule are
chemically stable below 200°C, indication that the prepared microcapsules have a
good thermal stability.
CHARECTERISATIOM OF MICROCAPSULE BY FTIR
It can be seen from figure 4 (a-c), the FTIR spectra of Urea-Formaldehyde
coated microcapsule, core chemical of the microcapsule and r5upture
microcapsule with water that all are matching at characteristic peaks of a N-H
stretching vibration at 1571cm-1 a C=O stretching vibration at 1650 cm-1 and C-H
stretching vibration at 1460 cm-1, C-N stretching vibrations are shown at 1286
and 1142 cm-1. This spectrum confirms that the shell material is made of urea-
formaldehyde polymer.
When the broken capsules are allowed to react with water it shows the sharp
absorption peaks at 1694 and 1562 cm-1 which represent for the presence of
urethane linkage only, which means core materials are active enough and are
reacting with water to form a urethane linkage.
SELF HEALING ABILITY
After successful preparation, the nano/micro capsule must be embedded in a
suitable polymer matrix for achieving self healing ability. In the present study we
have prepared different types of inorganic and polymeric capsules and all the
capsules are incorporated at different concentration in to the water based
emulsion and solvent based sol-gel polymer matrix. After the proper aging
coated panels scribed with the cut line are investigate for self healing ability.
Under this investigation, initial photograph of the cut line is store in digital
camera, a SEM and stereo microscope, and the sample are exposed in 3.5%
NaCI solution, after 24th of interval the sample are removed from the solution
and photograph of the cut panels are recorded in digital camera, SEM and stereo
microscope. From the different study, it has been observed that following
microcapsules are showing good self healing ability at 1-2% loading in polymer
matrix.
1. Polymeric capsule containing desmodure isocyanides
Derivative as core chemicals.
2. Polymeric capsule containing methyl methaacrylate as core
Chemical.
EFFECT OF HEAT ON SELF HEAING ABILITY
In order to investigate the effect of temperature on the performance of self
healing ability, the sample coated with self healing polymers are allowed to cured
and after seven days of curing the coated sample are heated at 200°C for three
hour and after normal cooling, panel are subjected for corrosion resistance and
self healing ability test. From the digital camera, SEM and stereo microscope
photograph it has been observed that coated sample retain their self healing
ability even after three hour of exposure at 200°C. But after the heat treatment,
all the samples show poor corrosion resistance properties.
CORROSION RESISTANCE STUDY
Coating performance: SST was carried out to see its corrosion resistance
properties. It was found that coated steel is giving 300-400 hrs. SST resistance
as compared to 2 hrs in case of bare steel.
WE CLAIM :
1. A process for preparing at least one microcapsule to provide self-healing
properties to corrosion-resistant coating compositions, comprising the
steps of:
- mixing in a container deionized water and polyvinyl alcohol of 5 wt% at
room temperature under continuous mechanical stirring mode;
- dissolving in said mixture urea, ammonium chloride, and resorcinol;
- adding core chemical to the solution including drop-wise addition of 1N
NaoH to maintain pH value between 2.0 to 4.0.
- applying an ultrasonic homoniser to the solution under continuous mixing
mode at room temperature at specified intensity;
- obtaining a 1:1.9 molar ratio of formaldehyde to urea by adding
formaline;
- heating the obtained emulsion at a rate of l°C/m upto about 55°C;
- switching off the stirrer and the heater after about 4-hours of continuous
agitation at 800-2000 rpm;
- separating under vacuum the suspension of microcapsules after ambient
cooling of the suspension;
- rinsing the microcapsules with deionized water and air-drying for about 48
hours.
2. The process as claimed in claim 1, wherein when the deiorized water is taken
about 200 ml, the polyvinyl alcohol, urea, ammonium chloride, and resorcinol
is used respectively at an amount of 0.5-15 ml, 0.5-15g, and 0.1-5g.
3. The process as claimed in claim 1, wherein the core chemical is selected from
a group consisting of modified isocyanides, phinolphtalein, and methyl
methacrylate.
4. The process as claimed in claim 1, wherein the formalin added in the solution
constitutes 37% formaldehyde at an amount of 12.67g.
5. The process as claimed in claim 1, wherein the outer is layer of the
microcapsule is covered with urea formaldehyde layer.
6. The process as claimed in claim 1, wherein; the inner layer of the
microcapsule is selected from the group consisting of aliphatic iso-cyanide or
it derivative, aromatic iso-cyanide or it derivative, acrylic acid, methyl
methacrylate, recorsenol and vegetable oil or it derivative.
7. A self healing microcapsule produced in a process as claimed in claims 1 to 4.
8. A process for the preparation of a self healing thin organic coating applicable
on steel substrate, comprising :-
- providing emulsion of methyl hydrogen silicon: 95-97% by weight;
- providing Mano pigment: 0.5-2% by weight;
- providing flash rust inhibitor 0.5-2% by weight;
- mixing adhesion Promoter: 0.5-2% by weight;
- adding nano capsule: 0.5-2% by weight; and
- continuously mixing at room temperature by a stirrer for a period
corresponding to selected quantity of the ingradients.
9. The process as claimed in claim 8, comprising adding :
Titania-precursor: 60-63% by weight;
Coupling agent-methyl hydrogen silocone : 36-39% by weight; and
Nanocapsule, capsule : 0.5-20% by weight.
10. The coating composition as claimed in claim 8, wherein said flash rust
inhibitor is selected from products like sodium nitrite, benzotriazole, a
mixture of several inhibitors, its composition being :
10-25% of C12-C14 (2-benzothiazolylthio) succinic acid tert 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; and
10-25% morpholine nenzoate.
11. The coating composition as claimed in claim 8, wherein said adhesion
promoter is selected from silicon modified acrylic resin and/or silicon
modified derivative.
12. The process as claimed in claim 9, wherein the said titanium precursor is
selected from titanium is opropoxide and ethylene glycol monoethyl either
13. The process as claimed in claim 9, wherein the said catalyst is acetic acid
to help stabilize the sol in presence of coupling agents like [2-(3,4-
epoxycyclohexyl) ethyl trimethoxy Silane] and [N-Phenyl-3 aminopropyl
trimethoxy Silane], 3-mercaptopropyltrimthoxy silane and
Methylhydrogenpolysiloxane.
14. A process for coating a substrate with coasting composition as claimed in
claim 8 or 9, comprising applying the coating composition on a substrate,
and drying the coated substrate at 100 to 200°C for 20 min to 2 hours.
15. The process as claimed in claim 14, wherein coating is applied by methods
such as dipping spraying , roll coating and brush coating.
16. The process as claimed in claim 14, wherein the substrate is coated to
give a coating thickness of 2 to 100 micron, and 1 to 50 micron after
drying.

The invention relates to a process for preparing at least one microcapsule to provide
self-healing properties to corrosion-resistant coating compositions, comprising the steps
of mixing in a container deionized water and polyvinyl alcohol of 5 wt% at room
temperature under continuous mechanical stirring mode; dissolving in said
mixture urea, ammonium chloride, and resorcinol; adding core chemical to the
solution including drop-wise addition of 1N NaoH to maintain pH value between
2.0 to 4.0. applying an ultrasonic homoniser to the solution under continuous
mixing mode at room temperature at specified intensity; obtaining a 1:1.9 molar
ratio of formaldehyde to urea by adding formaline; heating the obtained
emulsion at a rate of l°C/m upto about 55°C; switching off the stirrer and the
heater after about 4-hours of continuous agitation at 800-2000 rpm; separating
under vacuum the suspension of microcapsules after ambient cooling of the
suspension; rinsing the microcapsules with deionized water and air-drying for
about 48 hours.