Description:FIELD OF INVENTION
The invention relates to a hydrophilic coating composition, its process for preparation and a process for coating the composition, particularly a process for coating the composition on aluminium and its alloys for heat exchanger.

BACKGROUND OF THE INVENTION
Aluminum is the second most malleable and the sixth most ductile metal. Aluminum finds application in a huge variety of products including cans, foils, kitchen utensils, window frames, beer kegs, gas cylinders, and aero-plane parts, automotive parts etc.

Aluminum being an infinitely recyclable material is an important material of construction for various applications. Aluminum is non-toxic and has a high thermal conductivity.

One of the application of aluminum is as heat exchanging media. Aluminum sheets in very thin gauges have been used in heat exchangers and fins of aluminium are very closely spaced to improve efficiency. These heat exchangers are being used in various environmental conditions like salty, humid, dry etc. Aluminum or its alloys in such severe condition undergoes corrosion (Figure 1). Once the aluminium in heat exchanger starts to corrode it cannot be reversed as fins are very closely spaced. This results in reduced life of heat exchanger and its associated equipment.

To protect aluminium from corrosion, it is coated with a corrosion protection coating before use in heat exchangers. However, these corrosion protection coatings are hydrophobic in nature. Heat exchanger made with aluminium coated with a hydrophobic coating cannot be used at lower temperature with high humidity as the water from air gets condensed on the heat exchanger fins which resists air flow and hampers the air flow between the fins. This results in a decrease in efficiency of heat exchanger.

Hence, a corrosion resistant coating which has an improved wettability is required which will quickly condenses water and disperses it avoiding droplet formation.

SUMMARY OF THE INVENTION
In an aspect, the present invention relates to a hydrophilic coating composition comprising 4.0-6.5% wt. of ethenol polymer, 3.5-5.5% wt. of poly (1-carboxyethylene), 1.5-2.5% wt. of 2, 2’, 2’’- Nitrilotri(ethan-1-ol), 0.1-0.6% wt. of at least one wetting agent and water up to 100% wt. of the composition.

In another aspect, the invention relates to a process for preparation of a hydrophilic coating composition. The process comprises forming a mixture of 4.0-6.5% wt. of ethenol polymer with 22-36% wt. of water. The ethenol polymer is dissolved by heating the mixture to temperature in a range from 80-90°C. The mixture is then cooled to 50°C and stirred to form a polymer solution. Then, 3.5-5.5% wt. of poly (1-carboxyethylene), 1.5-2.5% wt. of 2, 2’, 2’’- Nitrilotri(ethan-1-ol), and 0.1-0.6% wt. of at least one wetting agent to the polymer solution are added to the polymer solution. Later, water is added to make up 100% wt. of the composition.

BRIEF DESCRIPTION OF DRAWINGS
Figure 1: Image of bare aluminium sheet after salt spray for 200 hours
Figure 2: Tube Fin Heat Exchange

DETAILED DESCRIPTION OF THE INVENTION
The term “coating” as used herein refers to covering that is applied to the surface of an object, usually referred to as the substrate to prevent direct environmental contact. The term “Heat exchanger” as used herein refers to a Tube Fin Heat Exchanger (Figure 2) a system used to transfer heat between a source and a working fluid consisting of tubes that pass through a dense fin stack that is mechanically supported by a mounting frame. The term “fin” (Figure -2) as used herein refers to a heat exchanger surface that extend from an object to increase the rate of heat transfer to or from the environment by increasing convection.

In an aspect, the invention relates to a hydrophilic coating composition.

The hydrophilic coating composition comprises 4.0-6.5% wt. of ethenol polymer, 3.5-5.5% wt. of poly (1-carboxyethylene), 1.5-2.5% wt. of 2, 2’, 2’’- Nitrilotri(ethan-1-ol), 0.1-0.6% wt. of at least one wetting agent and water up to 100% wt. of the composition.

The wetting agent is selected from ethylene oxide/ propylene oxide copolymer, polysorbate 80, ethoxylated surfactants, sorbitan monooleate, and methylated melamine or a combination thereof.

The wetting agents improved the wetting of the surface of aluminium or its alloy to be coated.

Examples of ethylene oxide/ propylene oxide copolymer include but are not limited to Synpronics LF30, Synpronics LF26 LQ. Example of ethoxylated surfactant include but is not limited to Synpronics A7. Other Examples of wetting agents include ATSURF G19-LQ and Cresemer SC 168-LQ.

The ethenol polymer is a water-soluble synthetic polymer and represented by the formula [CH2CH(OH)]n. The polymer is colourless and odourless. The ethenol polymer provides the building block for the polymer by cross linking reaction.

In an embodiment, the ethenol polymer has a hydrolysis value of minimum 98%, and viscosity of a 4% wt. solution in water at 20°C is in range of 5-6 mpa.S. The ethenol polymer contains a maximum of 2.5% of sodium acetate.

Poly(1-carboxyethylene) is a derivative of acrylic acid and is represented by the formula (CH2-CH-COOH)n. Poly (1-carboxyethylene) acts as a crosslinker to form three-dimensional network by chemical reaction during curing (heating).

In an embodiment, poly(1-carboxyethylene) preferably has a molecular weight in a range from 50,000-8,00,000.Viscosity of poly(1-carboxyethylene) is preferably 20,000~40,000 (mPa s) at a temperature of 25 °C.

2, 2’, 2’’- Nitrilotri(ethan-1-ol) is a viscous organic compound having a tertiary amine group and a triol group. It acts as an adhesion promoter improving the adhesion of the coating to the surface of aluminium or its alloy.

Water is used a media to dissolve the polymers and is preferably used in an amount of 85-90% wt. of the composition. Water used in the composition has a conductivity of less than 5 mS/m.

The hydrophilic coating composition addresses of the present invention the problem with the known coatings compositions for aluminium heat exchanger. The hydrophilic coating composition provides a coating having a contact angle of less than 15° on fins comprising aluminium or its alloys. This helps dissipation of condensed water on heat exchanger at low temperature and opens passage for air flow between the fins thereby improving the efficiency of heat exchanger.

The coating composition also dries quickly thereby increasing the productivity of fins, good surface finish to the fins and formability.

In another aspect, the invention relates to a process for preparation of a hydrophilic coating composition. The process comprises forming a mixture of 4.0-6.5% wt. of ethenol polymer with 22-36% wt. of water. The ethenol polymer is dissolved by heating the mixture to temperature in a range from 80-90°C. The mixture is then cooled to 50°C and stirred to form a polymer solution. Then, 3.5-5.5% wt. of poly (1-carboxyethylene), 1.5-2.5% wt. of 2, 2’, 2’’- Nitrilotri(ethan-1-ol), and 0.1-0.6% wt. of at least one wetting agent to the polymer solution are added to the polymer solution. Later, water is added to make up 100% wt. of the composition.

In an embodiment, the mixture of ethenol polymer and water is heated to temperature in a range from 80-90°C for a duration in a range from 2 to 3 hours.

The addition of poly (1-carboxyethylene), 2, 2’, 2’’- Nitrilotri(ethan-1-ol), the wetting agent and water in the polymer solution is carried out at ambient temperature (temperature range of 25-35 °C), and preferably after addition of each component, the polymer solution is mixed for 10 minutes.

In another aspect, the invention provides a process for coating a surface of an aluminium sheet. The process comprises applying the hydrophilic coating composition on the surface of the aluminium sheet. Then, the coated aluminium sheet is heated at a temperature in a range from 225-265°C and subsequently cooled.

The composition is applied to the aluminium sheet with a three roller applicator mechanism to get a dried film coating thickness in range of 0.2-1.5 GSM

The coated sheet is heated in an oven at a temperature in the range from 225-265°C for 12-30 seconds, preferably at a temperature in a range from 225-255°C.

The heated coated aluminium sheets are cooled to room temperature by passing through air or water quench rolls.

In an embodiment, the aluminium sheet comprises aluminium, its alloys or a combination thereof.

In a preferred embodiment, before applying the composition the aluminium sheet is cleaned with acid degreasing solution and subjected to pre-treatment to improve corrosion protection. Pretreatment is carried out by coating the aluminium sheet with Gardobond X4650/3 (BASF), Permatreat 1700 (BASF), Bondrite M-CR- 6207 (Henkel), Bondrite M-NT- 802 (Henkel), or Bondrite M-NT-1456 (Henkel).

In an embodiment, at least two coats of the composition are applied on the aluminium sheet.

EXAMPLES
Example 1: Hydrophilic coating composition of the present invention.
Table 1 below describes the hydrophilic coating composition of the present invention.

Table 1
Sr. No. Material % wt.
F33 F34 F40
1 Ethenol polymer
(Hydrolysis value > 98%) 6.3 4.7 4.4
2 Poly(1-carboxyethylene)
Mol. Wt.- 8,00,000 5.0 3.8 4.5
3 2,2',2''-Nitrilotri (ethan-1-ol) 2.3 1.8 1.7
4 Wetting agent (ethylene oxide/propylene oxide copolymer) 0.2 0.6 0.6
5 Water
86.2 89.2 88.8

Process for preparation: Ethenol polymer was mixed with 25%wt. of water and the mixture was heated to a temperature in a range from 80-90°C for a duration of 2-3 hours. The mixture was stirred continuously at high speed until ethenol polymer was completely dissolved resulting in a polymer solution. The polymer solution was then cooled to 50°C. Poly(1-carboxyethylene), 2,2',2''-Nitrilotri (ethan-1-ol) and the wetting agent were added to the polymer solution at ambient temperature (temperature range of 25-35°C) and mixed for 10 minutes after addition of each of the component. Then, water was added to the mixture to make the weight up to 100% and mixed for 10 minutes to form the hydrophilic coating composition.

Comparative Examples
A series of coating compositions were prepared having components out the range defined for the composition of the present invention and with different crosslinkers, adhesion promoters, wetting agent and solvents as described in Tables 2-6 below,

Table 2
Sr. No. Material % wt.
F44 F45 F46 F47
1 Ethenol polymer
(Hydrolysis value > 98%) 6.3 0 6.3 6.3
2 Poly(1-carboxyethylene)
Mol. Wt.- 8,00,000 0 5 5.0 5.0
3 2,2',2''-Nitrilotri (ethan-1-ol) 0 0 0 2.3
4 Wetting agent (ethylene oxide/propylene oxide copolymer) 0 0 0 0
5 Water
93.7 95 88.7 86.4

Table 3
% wt.
F1 F2 F3 F4 F5 F6 F7 F8 F9 F10
Component A: (Ethenol) 4.4 4.4 4.4 10.6 10.5 10.3 10.0 8.4 12.6 11.7
Crosslinker
Component B-1: Poly(1-carboxyethylene) Avg. Mol wt. 50000 0.0 0.0 0.0 11.7 10.9 11.5 9.8 8.6 6.5 8.8
Component B-2: Poly(1-carboxyethylene) Avg. Mol wt. 80000 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component B-3: SHELLPOL 940 (CARBOMER) 0.0 2.7 0.0 0 0 0 0 0 0 0
Component B-4: SHELLPOL 971 (CARBOMER) 0.0 0.0 4.4 0 0 0 0 0 0 0
Component B-5: SHELLPOL 934 (CARBOMER) 3.4 0.0 0.0 0 0 0 0 0 0 0
Component B-6: PEG-1500 (10% in water) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component B-7: PEG-6000 (10% in water) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.1 0.0 0.0
Adhesion promoter
Component C-1: 2,2',2''-Nitrilotri (ethan-1-ol) 0.0 0.0 0.0 0.0 0.0 2.6 2.5 2.0 0.0 0.0
Component C-2: Lithium hydroxide (10% in water) 1.3 1.3 1.3 0.0 2.8 0.0 0.0 0.0 0.0 0.0
Component C-3: Zirconium acetate 0.0 0.0 0.0 0.0 0.0 0.0 6.1 0.0 0.0 0.0
Component C-4: Colloidal Silica 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Wetting Agent
Component D-1: Tween 80 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component D-2: Synpronics A7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component D-3: ethylene oxide/propylene oxide copolymer 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component D-4: Span 80 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component D-5: Cymel 303 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component D-6: ATSURF G19-LQ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component D-7: Synpronics LF26 LQ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component D-8: Cresemer SC 168 -LQ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Solvent
Component E-1: Water 88.2 88.8 87.2 77.7 75.8 75.6 71.6 79.0 81.0 79.5
Component E-2: n-Butanol 2.7 2.7 2.7 0 0 0 0 0
Total 100.0 100.0 100.0 100.0 100.0 100.00 100.00 100.00 100.00 100.00

Table 4
% wt.
F11 F12 F13 F14 F15 F16 F17 F18 F19 F20
Component A (Ethenol) 10.0 9.9 8.8 10.0 6.8 6.6 6.8 6.1 6.7 6.7
Component B-1 Crosslinker 10.0 9.8 9.0 10.2 6.8 6.5 6.9 9.3 6.9 6.9
Component B-2 Crosslinker 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component B-3 Crosslinker 0 0 0 0 0 0 0 0 0 0
Component B-4 Crosslinker 0 0 0 0 0 0 0 0 0 0
Component B-5 Crosslinker 0 0 0 0 0 0 0 0 0 0
Component B-6 Crosslinker 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component B-7 Crosslinker 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component C-1 Adhesion Promotor 2.7 3.9 2.2 4.3 1.8 1.8 2.5 2.3 2.5 2.5
Component C-2 Adhesion Promotor 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component C-3 Adhesion Promotor 5.2 5.2 4.7 2.7 0.0 3.5 0.0 0.0 0.0 0.0
Component C-4 Adhesion Promotor 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component D-1 Wetting Agent 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0
Component D-2 Wetting Agent 0.5 0.5 0.9 0.0 0.9 0.8 0.8 0.8 1.26 1.67
Component D-3 Wetting Agent 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.00 0.00
Component D-4 Wetting Agent 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.00 0.00
Component D-5 Wetting Agent 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.00 0.00
Component D-6 Wetting Agent 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.00 0.00
Component D-7 Wetting Agent 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.00 0.00
Component D-8 Wetting Agent 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.00 0.00
Component E-1 Solvent (Water) 71.6 70.7 74.4 71.8 83.7 80.9 82.9 81.5 82.6 82.2
Component E-2 Solvent (n-Butanol) 0 0 0 0 0 0 0 0 0 0
100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

Table 5
%wt.
F21 F22 F23 F24 F25 F26 F27 F28 F29 F30
Component A (Ethenol) 6.7 6.9 7.3 6.7 6.7 6.5 7.0 7.2 6.8 6.9
Component B-1 Crosslinker 6.8 5.3 3.8 6.9 6.8 6.7 5.4 5.6 5.2 5.3
Component B-2 Crosslinker 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component B-3 Crosslinker 0 0 0 0 0 0 0 0 0 0
Component B-4 Crosslinker 0 0 0 0 0 0 0 0 0 0
Component B-5 Crosslinker 0 0 0 0 0 0 0 0 0 0
Component B-6 Crosslinker 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component B-7 Crosslinker 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component C-1 Adhesion Promotor 3.3 2.7 2.9 2.8 2.8 4.9 2.7 0.0 2.6 2.7
Component C-2 Adhesion Promotor 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component C-3 Adhesion Promotor 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component C-4 Adhesion Promotor 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 3.5 0.0
Component D-1 Wetting Agent 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component D-2 Wetting Agent 1.25 0.87 0.92 0.00 0.83 0.81 0.00 0.00 0.00 0.00
Component D-3 Wetting Agent 0.00 0.00 0.00 0.00 0.00 0.00 0.90 0.93 0.87 0.88
Component D-4 Wetting Agent 0.00 0.00 0.00 0.83 0.83 0.81 0.00 0.00 0.00 0.00
Component D-5 Wetting Agent 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.77
Component D-6 Wetting Agent 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Component D-7 Wetting Agent 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Component D-8 Wetting Agent 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Component E-1 Solvent (Water) 81.9 84.3 85.1 82.8 82.1 80.3 84.0 86.3 81.0 82.5
Component E-2 Solvent (n-Butanol) 0 0 0 0 0 0 0 0 0 0
100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

Table 6
%wt.
F31 F32 F35 F36 F37 F38 F39 F41 F42 F43
Component A (Ethenol) 6.8 8.0 6.7 6.2 5.7 6.4 4.7 4.7 4.6 4.7
Component B-1 Crosslinker 5.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component B-2 Crosslinker 0.0 0.0 3.4 4.8 5.9 5.1 3.7 3.6 3.6 3.6
Component B-3 Crosslinker 0 0 0 0 0 0 0 0 0 0
Component B-4 Crosslinker 0 0 0 0 0 0 0 0 0 0
Component B-5 Crosslinker 0 0 0 0 0 0 0 0 0 0
Component B-6 Crosslinker 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component B-7 Crosslinker 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component C-1 Adhesion Promotor 2.6 3.1 2.6 2.4 2.2 0.0 1.8 1.8 1.8 1.8
Component C-2 Adhesion Promotor 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component C-3 Adhesion Promotor 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component C-4 Adhesion Promotor 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component D-1 Wetting Agent 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Component D-2 Wetting Agent 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Component D-3 Wetting Agent 1.75 1.02 0.86 0.79 0.74 0.00 1.17 0.00 0.00 0.00
Component D-4 Wetting Agent 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Component D-5 Wetting Agent 1.75 2.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Component D-6 Wetting Agent 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.20 2.37 0.00
Component D-7 Wetting Agent 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.60
Component D-8 Wetting Agent 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Component E-1 Solvent (Water) 81.8 85.9 86.4 85.9 85.4 88.5 88.6 88.7 87.7 89.3
Component E-2 Solvent (n-Butanol) 0 0 0 0 0 0 0 0 0 0
100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

The components B-1 to B-7, C-1 to C-4 and D-1 to D-8 mentioned in Tables 4-6 are specified in Table 3. The compositions described in Tables 2-6 were prepared as per the process described in Example 1.

Example 2:
Coating an aluminium sheet with the coating composition
Aluminium sheets were cleaned with an acid degreasing solution and dried. The cleaned aluminium sheets were pre-treated for providing corrosion resistance. The pre-treated sheets were then coated with the coating composition of the example and comparative examples with a three roller applicator. The coated sheets were heated in a preheated oven at a temperature of 245°C for 12-30 seconds and then cooled to room temperature in an air or water quench roll. The procedure was repeated on the coating sheets such that at the aluminium were coated twice.

Characterisation
The coatings obtained in Example 2 was tested for the properties described in Table 7 below,

Table 7
Properties Standard Method Details Remarks
Dry film thickness [DFT] (GSM) Gravimetry Higher Coating GSM affects the drying time of coating. Lesser Coating GSM hampers anti-corrosive property and wettability/contact angle. Coating thickness (GSM) should in a range of 0.3-0.7 GSM such a that optimum hydrophilic property can be achieved with drying time < 20 Sec.
Peak metal temperature [PMT] (12-20 Sec) (°C) Over Temperature with calibrated thermometer Lesser PMT results in uncured coating hence, poor anti corrosive property. Higher PMT results in change of coating colour and thus undesirable surface finish. Hence it should be in range of 225-255°C.
MEK Rub ASTM D4752 Lesser MEK Rubs is due to of insufficient crosslinking, hence poor anti corrosive property. Higher MEK Rubs results into high anti-corrosive property. MEK rubs more than 50 are desirable.
Bend Test – Tape Adhesion ASTM D4145

Failure of test shows insufficient adhesion.

Cross hatch test – Tape Adhesion ASTM D3359
Ericsson Cupping- Tape adhesion ISO 20482
Impact Test - Tape adhesion ASTM E23
Copper Accelerated Acetic Acid salt Spray (CASS) Test ASTM B117 Failure of test shows poor anti-corrosion property.
Salt Spray Test ASTM D1193 Lesser Salt Spray Test Hours shows poor anti-corrosion property.
Contact angle (1- Poor & 5-Best)
Surface contact angle measurement

Lesser Rating shows poor Wettability/Hydrophilicity
Contact angle after 1 hr water running test (1- Poor & 5-Best)

Results
The results of the tests for the coatings obtained from the composition of the present invention described in Table 1 and the comparative Examples in Table 2 is tabulated in Table 8 below,

Table 8
Examples of present invention Comparative Examples
Property F33 F34 F40 F44 F45 F46 F47
Appearance Clear, Even Coating Clear, Even Coating Clear, Even Coating Clear, Even Coating Clear, Even Coating Clear, Even Coating Clear, Even Coating
DFT (GSM) 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3-0.7 0.3-0.7 0.3-0.7 0.3-0.7
PMT (°C) 225-255 225-255 225-255 225-255 225-255 225-255 225-255
MEK Rub >50 >50 >50 < 05 < 05 >50 >50
Bend Test – Tape Adhesion Pass Pass Pass ND ND Fail Pass
Cross hatch test – Tape Adhesion Pass Pass Pass ND ND Fail Pass
Ericsson Cupping- Tape adhesion Pass Pass Pass ND ND Fail Pass
Impact Test - Tape adhesion Pass Pass Pass ND ND Fail Pass
Accelerated CuSO4 Corrosion Pass Pass Pass ND ND ND Pass
Salt Spray Test > 2000 Hrs. >2000 Hrs. >2000 Hrs. ND ND ND ND.
Contact angle (1- Poor & 5-Best) 3 5 5 ND ND ND 2
Contact angle after 1 hr water running test (1- Poor & 5-Best) 3 3 4 ND ND ND 1
*ND=Not Determined

As seen from the tables above, The results for coatings of examples as per the present invention (F33, F34 and F40) provided optimum thickness and PMT suggesting a quick drying time, high anti-corrosive properties and a desirable surface finish. The high anti-corrosive property of the coating was also confirmed by higher rubs of MEK, passing of the accelerated copper sulphate (CuSO4) corrosion test and more than 2000 hours in salt spray test. The coatings also had higher rating of contact angle initially and after being subjected to water test indicating improvement of wettability of the aluminium surface suggesting that the efficiency of heat exchanger having such coated aluminium fins would be improved. Further, the coatings also passed all the adhesion tests suggesting that the coatings maintained its adhesive properties during formation of fin from the aluminium sheets.

Whereas comparative composition F44 containing only ethenol polymer and water and F45 containing only poly(1-carboxyethylene) and water had poor result of MEK rub test indicating poor anti-corrosive properties than that for composition F33 of the present invention. Further, the coating of comparative compositions F44 and F45 was not suitable MEK rub < 50 and therefore the adhesion, contact angle and resistance to corrosion by copper sulphate and salt spray not determined.

Coating of comparative composition F46 not containing the adhesion promoter and wetting agent provided acceptable results for dry film thickness, PMT and MEK rub suggesting improvement in anti-corrosive properties and wettability over coatings of comparative compositions F44 and F45. However, the coating of F46 failed the adhesion tests and thereby were not suitable and therefore, contact angle and corrosion resistance could not be determined.

Coating of comparative composition F47 did not contain the wetting agent and thereby had a poor rating of contact angle in comparison to coating of composition F33 as per the present invention having same composition as F47 and including 0.2% wt. of a wetting agent.

Further, coating of comparative composition F28 not containing adhesion promoter had average rating for contact angle but resulted in uneven coating (See results in Table 11 below) and therefore adhesion and corrosion resistance could not be determined.

The results show that all the components 4.0-6.5% wt. of ethenol polymer, 3.5-5.5% wt. of poly (1-carboxyethylene), 1.5-2.5% wt. of 2, 2’, 2’’- Nitrilotri(ethan-1-ol), 0.1-0.6% wt. of at least one wetting agent and water up to 100% wt. of the composition were required to provide a coating having desired properties of quick drying, anti-corrosion, wettability, adhesion, and surface finish.

The results of coatings obtained from the comparative Examples described in Tables 3-6 is tabulated in Tables 9-12.
Table 9
F1 F2 F3 F4 F5 F6 F7 F8 F9 F10
Appearance Clear, Even Coating Clear, Even Coating Clear, Even Coating Clear, even Coating Slight whitish even Coating Dull, Rough, Whitish Clear, even Coating Slight whitish uneven Coating Clear slight yellow, even Coating Clear, even Coating
DFT (GSM) 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7
PMT (12-20 Sec) (°C) 225-255 225-255 225-255 225-255 225-255 225-255 225-255 225-255 225-255 225-255
MEK Rub <10 <10 <10 ND ND ND ND ND ND ND
Bend Test – Tape Adhesion ND ND ND ND ND ND ND ND ND ND
Cross hatch test – Tape Adhesion ND ND ND ND ND ND ND ND ND ND
Ericsson Cupping- Tape adhesion ND ND ND ND ND ND ND ND ND ND
Impact Test - Tape adhesion ND ND ND ND ND ND ND ND ND ND
Accelerated CuSO4 Corrosion ND ND ND ND ND ND ND ND ND ND
Salt Spray Test ND ND ND ND ND ND ND ND ND ND
Contact angle 1 1 1 2 3 3 4 4 2 2
Adhesion 1 1 1 5 4 5 5 4 4 5
Appearance after 1 hr running water test Dull, Rough, Whitish Dull, Rough, Whitish Dull, Rough, Whitish Clear, even Coating Dull, Rough, Whitish Clear, even Coating Clear, even Coating Slight whitish uneven Coating Clear slight yellow, even Coating Clear, even Coating
Contact angle after 1 hr water running test 1 1 1 2 3 2 3 3 1 1
Adhesion after 1 hr water running test 1 1 1 5 3 3 5 2 4 5
*ND= not determined
Table 10
F11 F12 F13 F14 F15 F16 F17 F18 F19 F20
Appearance Dull, slight Rough, slight Whitish Dull, Rough, Whitish Dull, Rough, Whitish Slight white, even coating Clear, even Coating Slight Whitish uneven coating Clear, even Coating Clear, even Coating Slight Whitish, even coating Slight Whitish, even coating
DFT (GSM) 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7
PMT (12-20 Sec) (°C) 225-255 225-255 225-255 225-255 225-255 225-255 225-255 225-255 225-255 225-255
MEK Rub ND ND ND ND ND ND ND ND ND ND
Bend Test – Tape Adhesion ND ND ND ND ND ND ND ND ND ND
Cross hatch test – Tape Adhesion ND ND ND ND ND ND ND ND ND ND
Ericsson Cupping- Tape adhesion ND ND ND ND ND ND ND ND ND ND
Impact Test - Tape adhesion ND ND ND ND ND ND ND ND ND ND
Accelerated CuSO4 Corrosion ND ND ND ND ND ND ND ND ND ND
Salt Spray Test ND ND ND ND ND ND ND ND ND ND
Contact angle 5 5 5 5 5 5 5 4 5 5
Adhesion 5 5 4 5 5 5 5 5 5 5
Appearance after 1 hr running water test Dull, slight Rough, slight Whitish Dull, Rough, Whitish Dull, Rough, Whitish Slight white, even coating Clear, even Coating Whitish uneven coating clear slight white, coating clear slight white, coating Slight Whitish, even coating Slight Whitish, even coating
Contact angle after 1 hr water running test 3 4 3 2 3 3 3 2 2 3
Adhesion after 1 hr water running test 5 5 3 5 5 5 5 5 1 2
*ND= not determined
Table 11
F21 F22 F23 F24 F25 F26 F27 F28 F29 F30
Appearance Slight Whitish, even coating Clear, even Coating Slight Whitish, even coating Clear, uneven Coating Clear, uneven Coating Whitish, uneven Coating Slight Whitish, even coating Clear, uneven Coating Slight Whitish, even coating Clear, uneven Coating
DFT (GSM) 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7
PMT (12-20 Sec) (°C) 225-255 225-255 225-255 225-255 225-255 225-255 225-255 225-255 225-255 225-255
MEK Rub ND ND ND ND ND ND ND ND ND ND
Bend Test – Tape Adhesion ND ND ND ND ND ND ND ND ND ND
Cross hatch test – Tape Adhesion ND ND ND ND ND ND ND ND ND ND
Ericsson Cupping- Tape adhesion ND ND ND ND ND ND ND ND ND ND
Impact Test - Tape adhesion ND ND ND ND ND ND ND ND ND ND
Accelerated CuSO4 Corrosion ND ND ND ND ND ND ND ND ND ND
Salt Spray Test ND ND ND ND ND ND ND ND ND ND
Contact angle 2 3.5 3 2 3 3 3 2 4 3
Adhesion 3 5 5 4 4 4 5 5 5 5
Appearance after 1 hr running water test ND Slight Whitish, even coating Slight Whitish, even coating ND ND ND Slight Whitish, even coating ND Slight Whitish, even coating Slight Whitish, even coating
Contact angle after 1 hr water running test ND 3 2 ND ND ND 3 ND 3 2
Adhesion after 1 hr water running test ND 5 5 ND ND ND 5 ND 5 2
*ND= not determined

Table 12
F31 F32 F35 F36 F37 F38 F39 F41 F42 F43
Appearance Clear, uneven Coating Clear, even Coating Clear, even Coating Clear, even Coating Clear, even Coating Clear, even Coating Clear, even Coating Clear, even Coating Clear, even Coating Uneven coating wettability issue during coating
DFT (GSM) 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7 0.3 - 0.7
PMT (12-20 Sec) (°C) 225-255 225-255 225-255 225-255 225-255 225-255 225-255 225-255 225-255 225-255
MEK Rub ND ND ND ND ND ND ND ND ND ND
Bend Test – Tape Adhesion ND ND ND ND ND ND ND ND ND ND
Cross hatch test – Tape Adhesion ND ND ND ND ND ND ND ND ND ND
Ericsson Cupping- Tape adhesion ND ND ND ND ND ND ND ND ND ND
Impact Test - Tape adhesion ND ND ND ND ND ND ND ND ND ND
Accelerated CuSO4 Corrosion ND ND ND ND ND ND ND ND ND ND
Salt Spray Test ND ND ND ND ND ND ND ND ND ND
Contact angle 3 5 5 5 5 1 5 3 3 2
Adhesion 5 1 5 5 5 5 5 5 5 5
Appearance after 1 hr running water test Slight Whitish, even coating Clear, even Coating Clear, even Coating Clear, even Coating Clear, even Coating Clear, even Coating Clear, even Coating Clear, even Coating Clear, even Coating ND
Contact angle after 1 hr water running test 1 2 5 5 5 1 2 2 2 ND
Adhesion after 1 hr water running test 5 1 2 2 2 3 5 5 5 ND
*ND= not determined

Whereas, the Comparative Examples provided a coating having poor ratings for contact angle suggesting poor wettability of the surface of aluminium sheet with the coating. As the coatings of the Comparative Examples failed the adhesion test, they were not suitable and therefore corrosion resistance could not be determined.

The foregoing description of the disclosure has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to a person skilled in the art, the invention should be construed to include everything within the scope of the disclosure.
, Claims:
1. A hydrophilic coating composition comprising:
4.0-6.5% wt. of ethenol polymer;
3.5-5.5% wt. of poly (1-carboxyethylene);
1.5-2.5% wt. of 2, 2’, 2’’- Nitrilotri(ethan-1-ol);
0.1-0.6% wt. of at least one wetting agent; and
water up to 100% wt. of the composition.

2. The composition as claimed in claim 1, wherein the wetting agent is selected from ethylene oxide/ propylene oxide copolymer, polysorbate 80, ethoxylated surfactants, and sorbitan monooleate, or a combination thereof.

3. The composition as claimed in claim 1 or 2 wherein,
ethenol polymer has a hydrolysis value of minimum 98% and viscosity of a 4% wt. solution in water at 20°C is in range of 5-6 mpa.S; and
poly (1-carboxyethylene) has a molecular weight in a range from 50000-80000.

4. A process for preparation of a hydrophilic coating composition, the process comprising:
forming a mixture of 4.0-6.5% wt. of ethenol polymer with 22-36% wt. of water;
dissolving ethenol polymer in water by heating the mixture to a temperature in a range from 80-90°C;
cooling the mixture to 50°C;
stirring the mixture to form a polymer solution;
adding 3.5-5.5% wt. of poly (1-carboxyethylene), 1.5-2.5% wt. of 2, 2’, 2’’- Nitrilotri(ethan-1-ol), and 0.1-0.6% wt. of at least one wetting agent to the polymer solution; and
adding water to make up the weight to make up 100 % wt.

5. The process as claimed in claim 4, wherein mixture of ethenol polymer and water is heated for a duration in a range from 2 to 3 hours.

6. The process as claimed in claim 4 wherein poly (1-carboxyethylene), 2, 2’, 2’’- Nitrilotri(ethan-1-ol), the wetting agent and water are added in the polymer solution at ambient temperature.

7. A process for coating a surface of an aluminium sheet, the process comprising:
applying the composition as claimed in any one of claim 1-3 on the surface of the aluminium sheet;
heating the coated aluminium sheet at a temperature in a range from 225-265°C; and
cooling the heated aluminium sheet.

8. The process as claimed in claim 7, wherein the composition is applied on the aluminium sheet with a three roller applicator.

9. The process as claimed in claim 7, wherein heating of the coated aluminium sheet is carried out for a duration of 12-30 seconds.

10. The process as claimed in claim 7, wherein cooling of the heated aluminium sheet is carried out by air or water quench rolls.

11. The process as claimed in claim 7, wherein the aluminium sheet is cleaned with acid degreasing solution and subjected to pre-treatment before applying the composition onto the aluminium sheet.

12. The process as claimed in any one of claims 7-10, wherein at least two coats of the composition are applied on the aluminium sheet.