FORM 2
THE PATENTS ACT, 1970
(Act 39 of 70)
AND
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section10)
TITLE - DEVELOPMENT OF FAST CURE UNDERWATER EPOXV COATING
APPLICANT(S):
Name INDIAN INSTITUTE OF TECHNOLOGY_BOMBAY
Nationality: INDIAN
Address: Indian Institute of Technology Bombay, Powai
Mumbai - 400 076 Maharashtra, India.
The following specification particularly describes the invention and the manner in which it is to be performed.

Title:
Development of Fast Cure underwater Epoxy Coating
Field of Invention:
This invention relates to a fast cure underwater epoxy coating system which uses a unique combination of epoxy resins in combination with cycloaliphatic amine hardener and tertiary amine accelerator giving surface dry time of 2 hours with a thickness of about 300 microns with excellent hydrophobicity, flexibility, strength and corrosion resistance properties.
Background and Prior Art:
The present invention relates to a fast cure underwater epoxy coating composition which provides protection as well aesthetic appeal for repair and maintenance of piers, swimming pools, and contaminated tanks, wherein the surfaces to be coated are submerged under water most of the time. The coating can also be applied to other structures like loading docks, marine vessels and sweating pipes which are not inundated with water but acquire moisture due to their locations and functions.
Epoxy resin type paint for corrosion resistance have been coated on various steel structures such as drum gates or water gates, stakes, bridge piers which are constructed at sea shores, rivers, lakes or the like and which are located in water or which are in wet condition , for their protection or for aesthetic appearance. For example, JP-A-1-129054, JP-A-1-129070, JP-A-2-255879, JP-A-2-29479 and JP-A-4-320827 disclose underwater curable epoxy resin type coating material.
US006037435A, mentions the use of two component epoxy coating system for underwater application wherein the epoxy resin component is an epoxy resin mixture comprising a hydrophobic epoxy resin and a self-emulsifiable epoxy resin both of which are liquid at room temperature, and the curing agent is

composed partly or solely of a ketimine compound. However, the drawback of using such system is that the entire system as a whole is susceptible to water attack since the self-emulsifiable epoxy resin has hydrophilic groups which do not provide sufficient hydrophobic nature to the system which is a desired characteristic for underwater coatings.
In addition to the above drawback, the system also incorporates ketimine which decomposes into an amine and a carbonyl compound upon reaction with water. The amine group further functions as a curing agent and the carbonyl compound remains in the system and acts as a solvent for the system, thus delaying the curing time. The carbonyl compound can later be leached out of the system into the water and thus adds to the volatile organic content (VOC), a feature which is not desirable from the environmental point of view.
Object of Invention:
The present invention does not use any harmful solvents in the formulation however it uses a unique combination of cycloaliphatic amine hardener and tertiary amine accelerator along with the combination of epoxy resins to give a coating which cures underwater having improved properties.
Detail description of the invention:
The present invention does not use ketimine to enhance the curing reaction, whereas it uses tertiary amine accelerator tris (dimethylaminomethyl) phenol to enhance the curing mechanism along with cycloaliphatic diamine-Phenol adduct as a hardener thus reducing the hard dry time to about 1.5 to 2 hours of about 300 microns. The cycloaliphatic diamine used in this case is Isophorone Diamine which is commercially available. The properties like good hydrophobicity, adhesion and excellent chemical resistance for underwater application are achieved by making use of a unique combination of epoxy resins having equivalent weights of 180 and 650. Further to the above mentioned properties, good flexibility is achieved by making a unique combination of glass flakes and

glass fibers in the present system. A very high flexibility of the order of 170-180 degrees on cylindrical mandrel is achieved by making use of the said unique combination of glass flakes and glass fibers. A very good consistency of the coating system is obtained by making use of additional fibrous fillers, dispersing, wetting and defoaming additives available commercially.
A typical process of development of fast-cure underwater epoxy coating comprises development of two parts; development of resin (part A) and Hardener (part B) and then mixing the two and applying it on the substrate under water with the help of a power brush to form the coating. Development of resin which is part A is carried out in the method mentioned as follows:
Development of resin (part A): Calculated amount of the epoxy resins, silica and titania are added into a disperser along with wetting and dispersing, defomer, surface modifier and rheology modifier additive and dispersed for high speed for about 2 hours to obtain a homogeneous paste. After that glass flakes are added into the system and further dispersed for about 30 min. At last glass fibres are added along with the surface tension reducer additive (added at the last, as it does not require high shear) and are further dispersed only for 10-15 minutes (if dispersed for more time then fibres will break and will not help in flexibility of the coating) and is kept in a can.
Development of Hardener (part B): Hardener and the accelerator are mixed in a separate can according to their proportion as per the composition.
Later Part A is mixed with part B to form a uniform paste which is applied with the help of a power brush onto the substrate underwater to form a uniform thickness coating.
The present invention makes use of power brush for application of the coating under water. To the coating composition of the present invention, various additives, for example, a filler pigment such as silica, mica or glass flakes, a hiding pigment such as titanium oxide, glass fibers, and other additives such as a

dispersant agent, a defoaming agent, and a flow-controlling agent, may further be incorporated, as the case requires.
The total amount of such various pigments and aggregate is usually at the most 50 weight %, preferable from 30 to 50 weight %, in the coating material.
Now, the present invention will be described in further detail with reference to example/s. However, it should be understood that the present invention is by no means restricted to such specific example/s. In the example/s "parts" means "parts by weight".



Performance test:
a) Cross hatch tape adhesion test: It follows ASTM D3359. These test methods cover procedures for assessing the adhesion of coating films to metallic substrates by applying and removing pressure-sensitive tape over cuts made in the film.
b) Pull off adhesion test: It follows ASTM 4541. This test method covers a procedure for evaluating the pull-off strength (commonly referred to as adhesion) of a coating system from metal substrates. Failure will occur along the weakest plane within the system comprised of the test fixture, adhesive, coating system, and substrate, and will be exposed by the fracture surface.
c) Impact test: It follows ASTM D2247. This test method covers a procedure for rapidly deforming by impact a coating film and its substrate and for evaluating the effect of such deformation.

d) Flexibility test: It follows ASTM D522. Cylindrical Mandrel Bend Tester is used to determine the elasticity, adhesion and elongation of coatings on sheet metal. The specimen is clamped against a conical mandrel and is bent around the mandrel by a roller mounted on a hand operated lever. The diameter of the mandrel at the point where the coating starts to crack can be determined from a scale marked on the specimen clamp.
e) Shore D hardness test (ASTM D2240): Shore hardness is a measure of the resistance of material to indentation by 3 spring-loaded indenters. The higher the number, the greater the resistance. If the indenter completely penetrates the sample, a reading of 0 is obtained, and if no penetration occurs, a reading of 100 results. The reading is dimensionless. The Shore hardness is measured with an apparatus known as a Durometer and consequently is also known as 'Durometer hardness'. The hardness value is determined by the penetration of the Durometer indenter foot into the sample. The results obtained from this test are a useful measure of relative resistance to indentation of various grades of coating and polymers.
The above mentioned tests were carried out and the corresponding data tabulated in Table 2 &3.

From Table 1, 2 & 3 it is evident that just using IPD as a hardener in the coating composition takes a considerable amount of time to get touch/surface, hard and full dry, whereas in comparison to composition 3 and finial composition 4 it is observed that by using a (IPD+ Phenol+ benzyl alcohol) in combination with

accelerator Hardener the touch/surface, hard and full dry time was reduced drastically in comparison to earlier compositions which did not use these ingredients. Composition 4 contains IPD in combination with accelerator Hardener and the touch/surface, hard and full dry time was further reduced in comparison with the composition which used (IPD+ Phenol+ benzyl alcohol) as a Hardener. Thus, using IPD and accelerator Hardener proved much efficient in reducing the touch/surface, hard and full dry time of the final coating.
From Table 1, 2 & 3 it is evident that using glass flakes and Micacious Iron Oxide (MIO) as a standalone ingredient in respective compositions increases flexibility and hardness to some extent, however when glass flake is used in combination with glass fibers which is optimised in the coating system the flexibility and hardness of the coating system is increased manifolds.
From Table 1, 2 & 3 it is also evident that by using an optimised combination of epoxy, Hardener and accelerator Hardener a higher pull off adhesion and Shore D Hardness of almost 4.2 MPa and 90 D are obtained.

What is claimed is:
1. A fast-cure underwater epoxy coating composition which is free from any volatile organic components (VOC), the composition comprising:
a) two epoxy resin components (A and B) of different equivalent weights, the component A being liquid at room temperature and the component B being semi-solid at room temperature;
b) a cycloaliphatic amine-phenol adduct hardener in combination with a tertiary amine accelerator;
c) a combination of glass fibers and glass flakes;
d) hiding pigment and extender pigment; and
e) additives,
wherein the underwater epoxy coating gives enhanced quick surface dry time of utmost 2 hours, high flexibility and high adhesion at a thickness of 300um per coat when cured under water.
2. The fast-cure underwater epoxy coating composition according to claim 1, wherein the epoxy resin component A has an equivalent weight of 180 and the epoxy resin component B has an equivalent weight of 650.
3. The fast-cure underwater epoxy coating composition according to claim 1, wherein the cycloaliphatic amine hardener is Isophorone Diamine-phenol adduct.
4. The fast-cure underwater epoxy coating composition according to claim 1, wherein the tertiary amine accelerator is technically tris-(dimethylaminomethyl) phenol.
5. The fast-cure underwater epoxy coating composition according to claim 1, wherein the combination ratio of glass fibers to glass flakes is in a

range of 0.3 to 0.5, giving a very high flexibility of 170-180 degrees on cylindrical manderel.
6. The fast-cure underwater epoxy coating composition according to claim 1, wherein the hiding pigment used is titanium dioxide and the extender pigment used is silica.
7. The fast-cure underwater epoxy coating composition according to claim 1, wherein an adhesion of 4 to 6 MPa is achieved when cured under water.
8. The rast-cure underwater epoxy coating composition according to claim 1, wherein a coating thickness of 300μm per coat is achieved when cured under water.
9. A method of manufacturing of fast cure underwater epoxy coating composition, comprising the steps of:

a) dispensing two epoxy resin components (A and B) of different equivalent weights along with hiding pigment, extender pigment, wetting & dispersing, defomer, surface modifier and rheology modifier additives for 120 minutes on a high speed disperser to form a homogeneous paste;
b) adding and dispersing glass flakes to the homogeneous paste formed in step (a) for 30 minutes;
c) adding and dispersing in the homogeneous paste formed in step (b), glass fibers along with surface tension reducer additive and dispersing it for 10-15 minutes to form part I;
d) separately mixing a cycloaliphatic amine hardener and a tertiary amine accelerator to form part II; and
e) mixing the part I and part II to form the fast cure underwater epoxy coating composition.

10. The method according to claim 9, wherein the epoxy resin component A has an equivalent weight of 180 and the epoxy resin component B has an equivalent weight of 650.
11. The method according to claim 9, wherein the cycloaliphatic amine hardener is Isophorone Diamine-phenol adduct.
12. The method according to claim 9, wherein the tertiary amine accelerator is technically tris-(dimethylaminomethyl) phenol.
13. The method according to claim 9, wherein the combination ratio of glass fibers to glass flakes is in a range of 0.3 to 0.5, giving a very high flexibility of 170-180 degrees on cylindrical manderel.
14. The method according to claim 9, wherein the hiding pigment used is titania and the extender pigment used is silica.