Claims:WE CLAIM:
1. A single component coating composition, said composition comprising:
• an epoxy component in an amount in the range of 10 wt.% to 30 wt.% with respect to the total weight of the composition, wherein epoxy equivalent weight (EEW) of said epoxy component is in the range of 180 g/epoxy to 450 g/epoxy;
• an aminosilane component in an amount in the range of 10 wt.% to 40 wt.% with respect to the total weight of the composition, wherein the aminosilane component is at least one compound selected from the group of compounds consisting of aminosilane and aminosiloxane;
• an organosilane component in an amount in the range of 1 wt.% to 20 wt.% with respect to the total weight of the composition, wherein the organosilane component is at least one compound selected from the group consisting of trialkoxy, alkyltrialkoxy, phenyltrialkoxy, alkenyltrialkoxy, dialkyldialkoxy, dialkenyldialkoxy, alkyl-alkenyldialkoxy, fluorinated alkoxysilanes and tetraalkoxy compounds; and
• a mercaptosilane component in an amount in the range of 1 wt.% to 10 wt.% with respect to the total weight of the composition, wherein the mercaptosilane component is at least one compound selected from the group of compounds consisting of mercaptosilane and mercaptosiloxane; and
• an organic fluid comprising a first organic fluid and optionally a second organic fluid fully miscible in all proportions with said first organic fluid, wherein the first organic fluid is at least one selected from the group consisting of alcohols, polyols, glycols and glycol monoethers and the second organic fluid is at least one selected from the group consisting of solvents, esters, ketones, glycol polyethers, and ethers, wherein said organic fluid is present in an amount in the range of 40 wt.% to 70 wt.% with respect to the total weight of the composition and said second organic fluid is present in an amount up to 50% of the total organic fluid;
wherein said composition has an amine value in the range of 50 mgKOH/g to 300 mgKOH/g and viscosity in the range of 20 cps to 400 cps.

2. The composition as claimed in claim 1, wherein said first organic fluid is selected from the group consisting of isopropyl alcohol, methanol, ethanol, n-butanol, isobutanol, ethylene glycol, propylene glycol, propylene glycol methyl ether and propylene glycol propyl ether.
3. The composition as claimed in claim 1, wherein said epoxy component is at least compound selected from the group of compounds consisting of monoepoxy, polyepoxy, epoxysilane, epoxysiloxane and oligomers thereof.
4. The composition as claimed in claim 3, wherein said epoxy component is at least one monoepoxy compound selected from the group consisting of phenyl glycidyl ether, glycidyl ester of versatic acid and glycidyl neodecanoate.
5. The composition as claimed in any of claims 1 or 3, wherein said epoxy component is at least one polyepoxy compound selected from the group consisting of epoxy-novolac resin, high molecular weight epoxy solvent cut resin, liquid epoxy resin based on bisphenol-A, bisphenol F type epoxy resin, hydrogenated bisphenol A based epoxy resin and bisphenol A/F epoxy resin with monofunctional reactive diluent.
6. The composition as claimed in any of claims 1 or 3, wherein said epoxy component is at least one epoxysilane compound selected from the group consisting of glycidoxyalkyl trialkoxysilanes, glycidoxyphenyl trialkoxysilanes, glycidoxyalkyl dialkoxyalkylsilanes, glycidoxyphenyl dialkoxyalkylsilanes, glycidoxyalkyl dialkoxyphenylsilanes, glycidoxyphenyl dialkoxyphenylsilanes and glycidoxyphenyl dialkoxyalkylsilanes.
7. The composition as claimed in any of claims 1 or 3, wherein said epoxy component is at least one epoxysiloxane compound, wherein the epoxysiloxane compound is oligomer/s of at least one epoxysilane compound selected from the group consisting of glycidoxyalkyl trialkoxysilanes, glycidoxyphenyl trialkoxysilanes, glycidoxyalkyl dialkoxyalkylsilanes, glycidoxyphenyl dialkoxyalkylsilanes, glycidoxyalkyl dialkoxyphenylsilanes, glycidoxyphenyl dialkoxyphenylsilanes and glycidoxyphenyl dialkoxyalkylsilanesepoxysilanes.
8. The composition as claimed in claim 1, wherein said organosilane component is at least one compound selected from the group of compounds consisting of methyl trimethoxysilane, vinyltrimethoxysilane, 3-methacryloxypropyl trimethoxysilane, octyltriethoxysilane and trifluoropropyl triethoxysilane.
9. The composition as claimed in claim 1, wherein said organosilane component is at least one one tetraalkoxy compound selected from the group consisting of tetraethyl orthosilicate, tetramethyl orthosilicate and oligomers thereof.
10. The composition as claimed in claim 1, wherein said aminosilane component is at least one aminosilane compound selected from group consisting of 3-aminoethyltriethoxysilane, 3-aminopropyltriethoxysilane, n-pheylaminopropyltrimethoxysilane, trimethoxysilylpropyldiethylene triamine, 3-(3-aminophenoxy)propyltrimethoxysilane, aminoethylaminomethylphenyl trimethoxy silane, 2-aminoethyl-3-aminopropyl-tris-2-ethylhexoxysilane, n-amino-hexyl-amino propyltrimethoxysilane and tris-aminopropyltrimethoxyethoxysilane.
11. The composition as claimed in claim 1, wherein said aminosilane component is at least one aminosiloxane compound, wherein the aminosiloxane compound is oligomer/s of at least one aminosilane compound selected from the group consisting of 3-aminoethyltriethoxysilane, 3-aminopropyltriethoxysilane, n-pheylaminopropyltrimethoxysilane, trimethoxysilylpropyldiethylene triamine, 3-(3-aminophenoxy) propyltrimethoxysilane, aminoethylaminomethylphenyl trimethoxy silane, 2-aminoethyl-3-aminopropyl-tris-2-ethylhexoxysilane, n-amino-hexyl-amino propyltrimethoxysilane and tris-aminopropyltrimethoxyethoxysilane.
12. The composition as claimed in claim 1, wherein said mercaptosilane component is at least one mercaptosilane compound selected from group consisting of mercaptopropyltrimethoxysilane, mercapto propylmethyl dimethoxysilane, mercaptopropyltriethoxysilane and mercaptopropylmethyldiethoxysilane.
13. The composition as claimed in claim 1, wherein said mercaptosilane component is at least one mercaptosiloxane compound, wherein the mercaptosiloxane compound is oligomer/s of at least one mercaptosilane compound selected from the group consisting of mercaptopropyltrimethoxysilane, mercapto propylmethyl dimethoxysilane, mercaptopropyltriethoxysilane and mercaptopropylmethyldiethoxysilane.
14. The composition as claimed in claim 1, wherein said viscosity of said composition is stable and increases by a maximum of 15% by accelerated stability test.
15. The composition as claimed in claim 1, wherein said viscosity of said composition is stable and increases by 10% by accelerated stability test.
16. A process for preparing the coating composition as claimed in any of the claims 1 to 15, wherein said composition has amine value in the range of 50 mgKOH/g to 300 mgKOH/g and viscosity in the range of 20 cps to 400 cps, said process comprising step of reacting at least one epoxy component with at least one aminosilane component, at least one organosilane component and at least one mercaptosilane component, at a temperature in the range of 25 °C to 35 °C for a time period in the range of 2 to 6 hours.
17. The process as claimed in claim 16, wherein said process further comprises adding at least one organic fluid to the components..
, Description:FIELD
The present disclosure relates to a single component coating composition and a process for preparation thereof.
DEFINITIONS:
As used in the present disclosure, the following words and phrases are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
The expression “amine value” refers to a convenient way of measuring the amino content of a sample. It is analogous to acid value and is defined as the number of milligrams of KOH equivalent to the basicity in one gram of sample.
The expression “Dry film thickness (DFT)” refers to the thickness of a cured coating (having single or multiple layers) which is measured above the substrate.
The expression “Epoxy equivalent weight (EEW)” refers to the weight of the epoxy resin in grams that contains one equivalent of epoxy.
BACKGROUND
Two component coating compositions are commonly used for achieving a high crosslinking density for improving adhesion of such coatings onto a substrate. However, such two component systems are unstable and have limited pot life. Moreover, such systems need mixing of the components in appropriate ratios prior to use.
On the other hand, single component coating compositions are relatively easy to use and can be directly applied. However, single component systems also have stability limitations wherein the viscosity of the composition tends to increase drastically after some days of storage. Further, the composition requires incorporating additives or reagents for obtaining improved coating properties such as better adhesion, anti-static nature, easy cleaning, self-cleaning and anti-graffiti characteristics.
There is, therefore, felt a need to provide a single component coating composition that overcomes the above mentioned drawbacks.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a single component coating composition.
Another object of the present disclosure is to provide a single component coating composition with improved storage stability.
Still another object of the present disclosure is to provide a single component coating composition with improved adhesion on substrates such as metal or glass.
Yet another object of the present disclosure is to obtain a coating on a substrate with improved properties while minimizing the use of fillers or additives.
Yet another object of the present disclosure is to provide a process for preparing a single component coating composition.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY
The present disclosure provides a single component coating composition. The composition comprises an epoxy component, an aminosilane component, an organosilane component, a mercaptosilane component and an organic fluid. The composition has an amine value in the range of 50 mgKOH/g to 300 mgKOH/g and viscosity in the range of 20 cps to 400 cps.
The epoxy component is at least compound selected from the group of compounds consisting of monoepoxy, polyepoxy, epoxysilane, epoxysiloxane and oligomers thereof, wherein epoxy equivalent weight (EEW) of the epoxy component is in the range of 180 g/epoxy to 450 g/epoxy. The aminosilane component is at least one compound selected from the group of compounds consisting of aminosilane and aminosiloxane. The mercaptosilane component is at least one compound selected from the group of compounds consisting of mercaptosilane and mercaptosiloxane.
The organosilane component is at least one compound selected from the group consisting of trialkoxy, alkyltrialkoxy, phenyltrialkoxy, alkenyltrialkoxy, dialkyldialkoxy, dialkenyldialkoxy, alkyl-alkenyldialkoxy, fluorinated alkoxysilanes and tetraalkoxy compounds.
The organosilane component is at least one tetraalkoxy compound selected from the group consisting of tetraethyl orthosilicate, tetramethyl orthosilicate and oligomers thereof.
The organic fluid comprises a first organic fluid and optionally a second organic fluid fully miscible in all proportions with the first organic fluid. The first organic fluid is at least one selected from the group consisting of alcohols, polyols, glycols and glycol monoethers and the second organic fluid is at least one selected from the group consisting of solvents, esters, ketones, glycol polyethers, and ethers.
The amount of the epoxy component is in the range of 10 wt.% to 30 wt.% with respect to the total weight of the composition. The amount of the aminosilane component is in the range of 10 wt.% to 40 wt.% with respect to the total weight of the composition. The amount of the organosilane component is in the range of 1 wt.% to 20 wt.% with respect to the total weight of the composition. The amount of the mercaptosilane component is in the range of 1 wt.% to 10 wt.% with respect to the total weight of the composition. The organic fluid is present in an amount in the range of 40 wt.% to 70 wt.% with respect to the total weight of the composition and the second organic fluid is present in an amount up to 50% of the total organic fluid. The viscosity of the composition is stable and increases by a maximum of 15% by accelerated stability test.
The present disclosure provides a process for preparing the coating composition wherein the process comprises step of reacting at least one epoxy component with at least one aminosilane component, at least one organosilane component and at least one mercaptosilane component, at a temperature in the range of 25 °C to 35 °C for a time period in the range of 2 to 6 hours. The process further comprises adding at least one organic fluid to the components, for the preparation of the coating composition.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The coating composition of the present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates the graph representing the transmission data for hybrid coating obtained by using coating composition, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
Conventional two component based coating compositions combine a hardener with a base paint to obtain a hard and durable coating. However, such coatings need instant and vigorous mixing of these components in correct ratios to obtain the required quality of coating. Such systems also have a very short pot life.
Single component coating compositions are preferred alternatives over two component based systems mainly due to no requirement of hardener and avoidance of mixing ratios each time before use.
However, single component systems, especially based on epoxy/blocked amines such as ketimine of aminosilane have limited storage stability as the viscosity of the composition tends to change drastically on storage. Moreover, same composition may not show suitable adhesion on different substrates. Further, additives may be required in the composition for obtaining the final coating layer/s with desired characteristics. As an example, conventionally, anti-static agents such as long-chain alkyl phenols, ethoxylated amines and glycerol esters are incorporated in the conventional coating composition for imparting anti-static properties to the final coated layer/s for minimizing dust collection. Such additives could further add to the cost and also affect the stability of the composition.
In one aspect, the present disclosure envisages a single component coating composition that is storage stable and imparts improved characteristics to the final coating. The coating composition comprises an epoxy component, an aminosilane component comprising at least one compound selected from the group of compounds consisting of aminosilane and aminosiloxane, an organosilane component, and a mercaptosilane component comprising at least one compound selected from the group of compounds consisting of mercaptosilane and mercaptosiloxane and an organic fluid, wherein epoxy equivalent weight (EEW) of the epoxy component is in the range of 180 g/epoxy to 450 g/epoxy. Typically, the coating composition of the present disclosure, has an amine value in the range of 50 mgKOH/g to 300 mgKOH/g.
In accordance with the present disclosure, the organosilane component is at least one compound selected from the group consisting of trialkoxy, alkyltrialkoxy, phenyltrialkoxy, alkenyltrialkoxy, dialkyldialkoxy, dialkenyldialkoxy, alkyl-alkenyldialkoxy, fluorinated alkoxysilanes and tetraalkoxy compounds.
The organic fluid comprises a first organic fluid and optionally a second organic fluid fully miscible in all proportions with the first organic fluid. The first organic fluid is at least one selected from the group consisting of alcohols, polyols, glycols and glycol monoethers. In one embodiment, the organic fluid is isopropyl alcohol. The second organic fluid is at least one selected from the group consisting of solvents, esters, ketones, glycol polyethers, and ethers.
The organic fluid is present in the composition in an amount in the range of 40 wt.% to 70 wt.% with respect to the total weight of the composition. The second organic fluid is present in an amount up to 50% of the total organic fluid.
Typically, the first organic fluid is selected from the group consisting of isopropyl alcohol, methanol, ethanol, n-butanol, isobutanol, ethylene glycol, propylene glycol, propylene glycol methyl ether and propylene glycol propyl ether. In one embodiment, the first organic fluid is isopropyl alcohol.
The epoxy component comprises at least compound selected from the group of compounds consisting of monoepoxy, polyepoxy, epoxysilane, epoxysiloxane and oligomers thereof. The amount of the epoxy component is in the range of 10 wt.% to 30 wt.% with respect to the total weight of the composition.
Epoxy equivalent weight (EEW) is the weight of the epoxy resin in grams that contains one equivalent of epoxy. The value of epoxy equivalent weight (EEW) increases with the molecular weight of the epoxy resin.
The present disclosure uses an epoxy component having epoxy equivalent weight (EEW) in the range of 180 g/epoxy to 450 g/epoxy. In an embodiment, the epoxy component has epoxy equivalent weight (EEW) value of 220 g/epoxy.
The epoxy component having EEW value higher than the mentioned range leads to processing problems with the organic solvents used in the composition. Further, as the EEW value goes higher, the coating tends to have higher thermoplasticity, thereby reducing the chemical resistance of the coating thus formed. Furthermore, aminosilane component tends to reduce when epoxy component with higher EEW is used, thereby altering the overall proportion of aminosilane component and organosilane component which leads to undesirable change in properties such as reduction in gloss, transmittance and the like.
In one embodiment, the epoxy component is at least one monoepoxy compound selected from the group consisting of phenyl glycidyl ether, glycidyl ester of versatic acid and glycidyl neodecanoate.
In another embodiment, the epoxy component is at least one polyepoxy compound selected from the group consisting of epoxy-novolac resin, high molecular weight epoxy solvent cut resin, liquid epoxy resin based on bisphenol-A, bisphenol F type epoxy resin, hydrogenated bisphenol A based epoxy resin and bisphenol A/F epoxy resin with monofunctional reactive diluent. In one embodiment, the epoxy component is hydrogenated bisphenol A based epoxy resin.
In another embodiment, the epoxy component is at least one epoxysilane compound selected from the group consisting of glycidoxyalkyl trialkoxysilanes, glycidoxyphenyl trialkoxysilanes, glycidoxyalkyl dialkoxyalkylsilanes, glycidoxyphenyl dialkoxyalkylsilanes, glycidoxyalkyl dialkoxyphenylsilanes, glycidoxyphenyl dialkoxyphenylsilanes and glycidoxyphenyl dialkoxyalkylsilanes.
In another embodiment, the epoxy component is at least one epoxysiloxane compound, wherein the epoxysiloxane compound is oligomer/s of at least one epoxysilane compound selected from the group consisting of glycidoxyalkyl trialkoxysilanes, glycidoxyphenyl trialkoxysilanes, glycidoxyalkyl dialkoxyalkylsilanes, glycidoxyphenyl dialkoxyalkylsilanes, glycidoxyalkyl dialkoxyphenylsilanes, glycidoxyphenyl dialkoxyphenylsilanes and glycidoxyphenyl dialkoxyalkylsilanesepoxysilanes.
In one embodiment, the organosilane component is at least one compound selected from the group consisting of methyl trimethoxysilane, vinyltrimethoxysilane, 3-methacryloxypropyl trimethoxysilane, octyltriethoxysilane and trifluoropropyl triethoxysilane.
In another embodiment, the organosilane component is at least one tetraalkoxy compound selected from the group consisting of tetraethyl orthosilicate, tetramethyl orthosilicate and oligomers thereof. In an exemplary embodiment, the organosilane component is oligomer of tetraethyl orthosilicate.
Typically, the aminosilane component is at least one aminosilane compound selected from the group consisting of 3-aminoethyltriethoxysilane, 3-aminopropyltriethoxysilane, n-pheylaminopropyltrimethoxysilane, trimethoxysilylpropyldiethylene triamine, 3-(3-aminophenoxy) propyltrimethoxysilane, aminoethylaminomethylphenyl trimethoxy silane, 2-aminoethyl-3-aminopropyl-tris-2-ethylhexoxysilane, n-amino-hexyl-amino propyltrimethoxysilane and tris-aminopropyltrimethoxyethoxysilane. In one embodiment, the aminosilane component is 3-aminoethyltriethoxysilane.
Typically, the aminosilane component is at least one aminosiloxane compound, wherein the aminosiloxane compound is oligomer/s of at least one aminosilane compound selected from the group consisting of 3-aminoethyltriethoxysilane, 3-aminopropyltriethoxysilane, n-pheylaminopropyltrimethoxysilane, trimethoxysilylpropyldiethylene triamine, 3-(3-aminophenoxy) propyltrimethoxysilane, aminoethylaminomethylphenyl trimethoxy silane, 2-aminoethyl-3-aminopropyl-tris-2-ethylhexoxysilane, n-amino-hexyl-amino propyltrimethoxysilane and tris-aminopropyltrimethoxyethoxysilane.
Typically, the mercaptosilane component is at least one mercaptosilane compound selected from the group consisting of mercaptopropyltrimethoxysilane, mercapto propylmethyl dimethoxysilane, mercaptopropyltriethoxysilane, and mercaptopropylmethyldiethoxysilane.
Typically, the mercaptosilane component is at least one mercaptosiloxane compound, wherein the mercaptosiloxane compound is oligomer/s of at least one mercaptosilane compound selected from the group consisting of mercaptopropyltrimethoxysilane, mercapto propylmethyl dimethoxysilane, mercaptopropyltriethoxysilane and mercaptopropylmethyldiethoxysilane.
The amount of aminosilane component is in the range of 10 wt.% to 40 wt.% with respect to the total weight of the composition. The amount of organosilane component is in the range of 1 wt.% to 20 wt.% with respect to the total weight of the composition. The amount of mercaptosilane component is in the range of 1 wt.% to 10 wt.% with respect to the total weight of the composition.
The coating composition of the present disclosure is storage stable. The viscosity of the coating composition does not change much even on storage. In one embodiment, the viscosity is checked after storage of 30 days at 55 °C.
In one embodiment, the viscosity of the composition is stable and increases by a maximum of 15% by accelerated stability test. In another embodiment, the viscosity of the composition is stable and increases by 10% by accelerated stability test.
In second aspect, the present disclosure provides a process for preparing the coating composition having amine value in the range of 50 mgKOH/g to 300 mgKOH/g, wherein the process comprises reacting at least one epoxy component with at least one aminosilane component, at least one organosilane component and at least one mercaptosilane component, at a temperature in the range of 25 °C to 35 °C for a time period in the range of 2 to 6 hours.
In an embodiment, the temperature is 30 °C and the time period is 3 hours.
The process further comprises adding to the components, at least one organic fluid.
The organic fluid comprises a first organic fluid and optionally a second organic fluid fully miscible in all proportions with the first organic fluid, wherein the first organic fluid is at least one selected from the group consisting of alcohols, polyols, glycols and glycol monoethers. Typically, the second organic fluid is at least one selected from the group consisting of solvents, esters, ketones, glycol polyethers, and ethers. The solid content of the coating composition is in the range 1 wt.% to 90 wt.%. In one embodiment, the solid content of the coating composition is in the range of range 20 wt.% to 60 wt.%. In another embodiment, the solid content of the coating composition is in the range of range 30 wt.% to 40 wt.%. The amount of solid content in the composition depends on the application requirements such as dry film thickness (DFT), stability of the composition and cost factors.
The process further comprises adding at least one moisture scavenging agent in the preparation of the coating composition. In one embodiment, the moisture scavenging agent is triethyl orthoformate.
The coating composition of the present disclosure is suitable for substrates such as glass or metal. The coating thus formed on such substrates, has good adhesion retention and does not delaminate easily even on exposure to the natural environment for a period of several days.
The coating composition of the present disclosure is applied onto substrates by using conventional techniques such as spraying, brush coating, dip coating and the like. The applied coatings are self-catalyzed and have ability to cure with moisture to form a hard coating layer/s under ambient conditions at a temperature range of 25 °C to 45 °C. In one embodiment, the hard coating layer/s have value of Dry Film Thickness (DFT) in the range of 1µm to 30 µm. The hard coating layer/s are clear and transparent in nature with good mechanical properties including scratch hardness, taber abrasion, nail hardness and pencil hardness.
The hard coating layer/s also exhibit inherent anti-static properties without the need for adding any anti-static agents. In an embodiment, the coatings of the present disclosure have surface resistivity value in the range of 106 ?/sq to 1010 ?/sq.
The present disclosure provides a single component coating composition with high storage stability, which on application onto a substrate results in hard coating layer/s or a hybrid coating. The hybrid coating thus obtained has good mechanical properties and advantageous characteristics such as good self-cleaning, easy cleaning, inherent anti-static properties and anti-graffiti properties.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
Experiment 1:
Coating composition in accordance with the present disclosure comprising epoxy resin, aminosilane, mercaptosilane oligomer and oligomeric ethyl silicate:
Cycloaliphatic epoxy resin YDH 3000 having epoxy equivalent weight (EEW) value of 220 g/epoxy (Diglycidyl ether of hydrogenated bisphenol-A) (26 g) and isopropanol (IPA) (20 g) were weighed in and mixed uniformly to obtain a mixture. To this mixture, Metasil 40 (oligomeric ethyl silicate) (20 g) was added in a controlled manner and mixed thoroughly to obtain a homogenous mixture. After homogenization, 3-aminopropyl triethoxysilane (AMEO) (40 g) was added in a dropwise manner for a period of about 15 to 20 minutes, followed by addition of Coatosil T cure (oligomer of mercaptosilane) (2 g) and triethyl orthoformate (moisture scavenger) (0.5g). The obtained mixture was stirred at 250 rpm for 3 hours under ambient conditions (30 ?C) to obtain the coating composition A.
Experiment 2:
Application of coating composition onto substrates:
The coating composition A as prepared in Experiment 1, was applied onto metal and glass substrates. The application was done using spraying technique wherein the viscosity was adjusted using isopropyl alcohol (IPA) as the thinning solvent. The applied coatings were allowed for ambient curing for 48 hours to obtain hard coating layer/s on the substrates (hybrid coating). The hybrid coating is subjected to measurement of mechanical properties such as pencil hardness, scratch hardness, pendulum hardness and taber abrasion. Other properties such as surface resistivity, adhesion retention, dirt pickup resistance (DPUR) and anti-graffiti property have also been measured. Dry film thickness (DFT) was measured using a DFT meter (Positector 6000 (by deflesco). Scratch hardness was measured on a Sheen automatic scratch hardness tester. Taber abrasion was measured on a Teledyne Taber abrasion instrument (Model 503) using CS 10 wheels for 1000 cycles and a 1 kg load. Crosscut adhesion was evaluated as per ASTM D 3359. The pendulum hardness of the panels was tested by using Pendulum hardness tester, from Braive Instruments (Persoz unit). The pencil hardness of the clearcoats was measured using Mitsubishi pencils from 3B to 3H.
Table 1: Coating property measurements for coating composition A applied on a substrate
Sr. No. Property Substrate Value
1. Dry Film Thickness (DFT) MS panel
30 µm
2. Scratch Hardness 2100 g
3. Taber Abrasion (CS 10-1000C) 4.2 mg
4. Surface resistivity 106 ?/sq
5. Pencil Hardness Glass panel
7H
6. Adhesion (glass panel) 5B
7. Pendulum Hardness 208
The coating shows excellent (5B) adhesion to glass. It is mechanically strong as indicated in the results obtained for pencil hardness (7H) and pendulum hardness (208).
For metal substrate, the coating shows good mechanical strength (2100 g scratch hardness) and good abrasion resistance (4.2 mg loss after 10000 cycles, CS-10 wheels).
Experiment 2a: Comparative measurement data for surface resistivity
The coating composition A as obtained in experiment 1 was applied as DTM (direct to metal). The hybrid coating thus obtained was measured for surface resistivity. Surface resistivity was measured using a surface resistivity meter (Trek 152-1). The results were compared with other organic coatings on the same substrate obtained by applying acrylic polyurethane (PU) composition and acrylic melamine formaldehyde (MF) composition. The acrylic polyurethane (PU) coating composition was prepared from acrylic polyol (OH value = 140 mg KOH/g) having glass transition temperature (Tg) of 20 °C and 60% solids in o-xylene is cured using the isocyanate Desmodur N3600 (1:1.1, OH: NCO ratio). The acrylic melamine formaldehyde (MF) resin used for curing the acrylic polyol was Resimine 5901 (74:26 ratio) at 140 °C/30 minutes.
Table 2: Comparative measurement data for surface resistivity
Coating used DTM (direct to metal) application
Coating composition A (experiment 1) 106 ohm
Acrylic PU coating 109 – 1010 ohm
Acrylic MF coating 1010 – 1011 ohm
As shown in Table 2, the hybrid coating obtained by using the coating composition of the present disclosure (coating composition A) gives a surface resistivity value of 106 ohm indicating it is displaying ESD (electrostatic dissipative properties). Thus, it has an inbuilt anti-static property without the need to add any anti-static additives. The acrylic polyurethane and acrylic MF coating show high values of surface resistivity (109 to 1011) indicating they are having insulation characteristics.
Experiment 2b: Comparative measurement data for adhesion retention
The coating composition A as obtained in experiment 1 was applied on glass. The hybrid coating thus obtained was measured for adhesion retention. The results were compared with other coatings (acrylic PU composition as used in Experiment 2a). The adhesion was also measured after exposure to the natural environment for a period of 60 days, including monsoon exposure. The results are summarized in Table 3.
Table 3: Comparative measurement data for adhesion retention
Coating type Adhesion on glass (cross cut) Adhesion after 60 days natural exposure (including rains)
Coating composition A (experiment 1) 5B Pass
Acrylic PU coating Fails Fails (delamination)
It was observed that the adhesion of the synthesized coatings to glass is excellent (5B) (As checked by cross cut adhesion tape test after 24 hours curing).
It was also observed that there was no delamination of the coating and there is good adhesion retention of the hybrid coating (obtained using coating composition A) whereas the acrylic PU coating had lost adhesion on glass and also delaminated.
Experiment 2c: Comparative measurement data for dirt pickup resistance (DPUR):
The hybrid coating obtained by using the coating composition A was measured for dirt pickup resistance test. The coating was cast on a white Laneta paper followed by curing for 7 days. The paper was cut into white rectangular strips of appropriate size that could fit in a rectangular DPUR box. Charcoal/Terrace dust (1g) was taken in the DPUR box. The box was shaken in forward and backward motion for 40 cycles. The strip was removed from the box and the loose dust was removed by gently tapping behind the strip. A comparative visual rating is given in Table 4.
The results were compared to other coatings (acrylic PU composition as used in Experiment 2a). The visual Rating was given on a scale of 1 to 10 where 1 indicates the lowest and 10 indicates the highest.
Table 4: Comparative measurement data for dirt pickup resistance (DPUR) using charcoal and terrace dust
Coating type Charcoal test Dirt pickup after 60 days natural exposure (including rains)
Hybrid coating (experiment A) 6/10 8/10
Acrylic PU coating 1/10 5/10
After DPUR testing, it was observed that the hybrid coating showed a better dirt pickup resistance (DPUR) compared to the acrylic PU coating. The hybrid coatings were visually less soiled as compared to the acrylic PU coating. The ratings on a scale of 1 to 10 are given in Table 4.
Experiment 2d: Comparative measurement data for Anti-graffiti characteristics:
The hybrid coating as obtained in experiment 2 (by using composition A), was studied for anti-graffiti properties by using different stains such as permanent marker, sketch pens, white board marker and water based paint. The stains applied were allowed to dry for 4 hours and then attempted for cleaning using dry cloth wiping. All stains were easily removed by using dry cloth showing the easy cleaning property of the hybrid coating.
Experiment 2e: Comparative measurement data for transmission property:
The hybrid coating (obtained by using composition A) was studied for transmission data as shown in Figure 1. It can be observed from Figure 1 that the light transmission of the hybrid coating overlaps with the blank glass slide over the given range of wavelength. The acrylic polyurethane coating is provided for comparison.
TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a single component coating composition that:
- is storage stable;
- has better adhesion to substrates like glass or metal than conventional coating compositions; and
- imparts improved properties to the coating layer/s while minimizing the use of fillers or additives.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.