Description:FIELD OF THE INVENTION
[001] The present invention relates to a coating composition for metal sheets or containers, more particularly to a quick drying hydrophile organic coating composition for aluminum or tin containers. The present invention also relates to a process of preparing the coating composition and method of coating the same.

BACKGROUND OF THE INVENTION
[002] Aluminum has various applications due to its light weight, soft and malleable nature. Aluminum being infinitely recyclable material is important material of construction for various application. Aluminum is non-toxic, has a high thermal conductivity, has excellent corrosion resistance, and can be easily cast, machined, and formed. It is also non-magnetic and non-sparking. It is the second most malleable metal and the sixth most ductile.
[003] Aluminum finds its 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. It is often used as an alloy because aluminum itself is not particularly strong. Alloys with copper, manganese, magnesium, and silicon are lightweight but strong.
[004] Aluminum sheets as heat exchanging media is one of the important applications. Aluminum sheets in very thin gauges being used in heat exchanges and they are very closely spaced to improve the efficiency. These heat exchangers are being used in various environmental conditions like salty, humid, dry etc. Bare aluminum or its alloys in such severe condition can undergoes corrosion. Once corrosion started in aluminum heat exchanger can be corrected as fins are very closely spaced. This results in the reduction of the usable life of heat exchanger & associated equipment.
[005] To improve the usable life of heat exchanger corrosion resistance coating is being used. However, these coated heat exchangers can’t be used at lower temperatures where the humidity is significant. Water from air gets condensed on these heat exchanger fins and air flow between the fins gets hampered.
[006] Hence, to improve the wettability of corrosion protection coatings additional hydrophile coating is being used. Hydrophile coating improves the wettability and helps water quickly condense and disperse and resist the droplet formation.
[007] Regular coatings available in market does not provide adequate wettability, required quick drying time and surface finish.
[008] Owing to the foregoing problems, various coating compositions have been formulated which address the issues of coatings known in the art. Particularly, these compositions address the issues regarding the adequate wettability, required quick dry time and surface finish. It is therefore an object of the invention to develop a quick drying organic hydrophile coating, a process to prepare the coating and its application on aluminum for use on aluminum sheets, preferably for heat exchanger application.

SUMMARY OF THE INVENTION
[009] One aspect of the present invention provides an organic hydrophile coating composition comprising Component A selected from NCT composite based on nanocrystalline cellulose (NCC) and nano-TiO2 (NT) which is grafted with 3-aminopropyltrimethoxy silane (APTMS), Component B selected from a resin polymer and Component C selected from a solvent.
[010] Another aspect of the present invention relates to a process for preparing the organic hydrophile coating composition for metal sheet or container. The process for preparing the coating composition comprising the steps: a) adsorption of NT on NCC with ultrasonication at room temperature, followed by simultaneous cycles of magnetic stirring and sonication with at a predetermined time interval to achieve a solution of NCT composite, b) centrifugation of the solution of NCT composite to recover solvent and solid NCT composite, c) drying the solid NCT composite, d) modification of solid NCT composite by grafting with APTMS in an aqueous alcohol solution and acid catalyst to provide a NCT suspension, e) continuous stirring of the NCT suspension at a predetermined pH to provide grafted NCT composite, f) blending predetermined amounts of the grafted NCT composite, resin polymer and a solvent to provide the hydrophile coating.
[011] Another aspect of the present invention relates to a method of coating metal sheet with the organic hydrophile coating composition of the present invention. The method of coating metal sheet, comprising the steps: a) degreasing of a metal sheet with water and drying to remove the residual oil and smut on the sheet; b) coating the degreased metal sheet with a corrosion protection coating composition using three roller applicator mechanism of appropriate thickness; c) drying the coated metal sheet in oven for less than 15 sec; d) cooling the coated metal sheet to room temperature with chilled rolls; e) coating the sheet obtained in step (d) with the coating composition of the present invention with three roller applicator mechanism of appropriate thickness followed by drying to get final dried film coating on the metal sheet.
[012] Another aspect of the present invention relates to the use of the organic hydrophile coating composition for metal sheets or container, preferably on aluminum sheets for heat exchanger application.

BRIEF DESCRIPTION OF THE DRAWINGS
[010] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 shows graphical representation of ssynthesis of NCT Composite.
Figure 2 shows Contact Angle (Picture) of droplet after dipping in water for 160 Hr. for the coating comprising 2% component ‘A’.
Figure 3 shows Contact Angle (Picture) of droplet after dipping in water for 160 Hr. for the coating comprising 5% component ‘A’.
DETAILED DESCRIPTION OF THE INVENTION
[001] The present invention discloses a hydrophile coating composition comprising component ‘A’ selected from NCT composite based on nanocrystalline cellulose (NCC) and nano-TiO2 (NT) which is grafted with 3-aminopropyltrimethoxy silane (APTMS), component ‘B’ selected from a resin polymer and component ‘C’ selected from a solvent.
[002] As used herein, the term “composition” refers to those formulations which function are prepared as mixture, amalgam or blend for coating a metal surface. The composition includes a homogenous or heterogeneous solution and similar formulations known to a person skilled in the art.
[003] As used herein, NCT composite is based on nanocrystalline cellulose (NCC) and nano-TiO2 (NT) which is grafted with 3-aminopropyltrimethoxy silane (APTMS).
[004] The NCT composite is prepared by the adsorption of NT on NCC under the ultrasonication process at room temperature. The synthesized NCT composite was further modified by grafting with APTMS.
[005] In a preferred embodiment, hydrophile coating composition comprises 1 to 5 parts by weight of component A, 75 to 90 parts by weight of component Band 10 to 20 parts by weight of component C based on the total weight of the composition.
[006] In a preferred embodiment, the nanocrystalline cellulose (NCC) is preferably selected from spray dried powder with bulk density 04-06 g/cm3 and moisture =<6 %, preferably from 0 to 6%.
[007] In a preferred embodiment, the nanocrystalline cellulose (NCC) is preferably based on particle size range 1-50 µm.
[008] In a preferred embodiment, the nano-TiO2 (NT) is preferably selected from the powder particle size range 10-40 nm and specific surface area (SSA) 160+/-30 m2/gram.
[009] As used herein, the term “resin polymer” refers to acrylic resin or acrylate resins, preferably based on commercial acrylic resin preferably selected from PIDICRYL 3539, PRIMAL™ AC-2337, REVACRYL AE6030.
[010] In a preferred embodiment, the solvent is selected from water.
[011] In another aspect, the present invention discloses a process for preparing the coating composition. The process comprising the following steps:
a. adsorption of NT on NCC with ultrasonication at room temperature, followed by simultaneous cycles of magnetic stirring and sonication with the same time interval to achieve a solution of NCT composite,
b. centrifugation of the solution of NCT composite to recover the solvent and solid NCT composite,
c. drying the solid NCT composite,
d. modification of solid NCT composite by grafting with APTMS in an aqueous alcohol solution and acid catalyst to provide a NCT suspension,
e. continuous stirring of NCT suspension at a predetermined pH to provide grafted NCT composite,
f. blending predetermined amounts of grafted NCT composite, commercial acrylic resin polymer and solvent to provide the hydrophile coating.
[012] In a preferred embodiment, the ratio of NCC to NT and APTMS was taken as 1:1.5 (i.e., NCC: NT and APTMS).
[013] In a preferred embodiment, the acid catalyst is selected from acetic acid.
[014] In a preferred embodiment, the predetermined pH is in the range of 4 to 5, preferably 4 to 4.5.
[015] In a preferred embodiment, drying of the solid NCT composite is done at 55 to 65 oC, preferably at 60 oC.
[016] In another aspect, the present invention discloses a method of coating metal sheet or container with the organic hydrophile coating composition of the present invention. Typically, the method of coating comprises the following steps:
a) degreasing of metal sheet with water and drying to remove the residual oil and smut on sheet;
b) coating the metal sheet with corrosion protection coating composition using three roller applicator mechanism of appropriate thickness;
c) drying the coated metal sheet in oven for less than 15 sec;
d) cooling the coated metal sheet to room temperature with chilled rolls;
e) coating the sheet obtained in step (d) with the coating composition claimed in claims 1 to 6 with three roller applicator mechanism of appropriate thickness followed by drying to get final dried film coating on the metal sheet.
[017] In a preferred embodiment, the the metal sheet or container is selected from aluminum or tin.
[018] In a preferred embodiment, the final dried film coating has a thickness of .2 to 0.8 GSM.
[019] In a preferred embodiment, the drying in oven is between 200 to 300 oC, preferably between 225 to 265 oC.
[020] As used herein the degreasing and drying of metal sheet is preferably done in 4% sulfuric acid solution at 45 oC. Metal sheet is then preferably rinsed with demineralized water, and preferably dried in air drying oven from 125 to150 oC.
[021] As used herein “three roller applicator” refers to three roll semi reverse and three roll full reverse applicators.
[022] As used herein “chilled rolls” refer to hollow rolls through which refringent is passed. Chilled rolls act as heat exchanger and reduce the coated metal sheet temperature to ambient conditions before coiling.
[023] Advantageously, the coating composition of the present invention when applied on aluminum sheet provides wettability (Water contact angle < 15o). This helps in dissipation of condensed water on heat exchangers at low temperatures and open passage for air flow between the fins. This helps in improving the heat exchanger efficiency as well. Accordingly, the coating compositions are particularly useful on aluminum sheets for heat exchanger application.
EXAMPLE
[024] The following examples are illustrative of the invention but not limitative of the scope thereof.
[025] Materials and Methods
[026] Materials: Pidilite P 3539 (Acrylic Emulsion), Acetone LR Grade, Absolute Alcohol LR Grade, Acetic Acid LR Grade, Nano Titanium Dioxide rutile NT, Nanocrystalline Cellulose and 3-APTMS 97% LR Grade.
[027] Synthesis of NCT composite: The adsorption of NT on NCC was achieved with the ultrasonication process at room temperature, and the composite was synthesized. The ratio of NCC to NT and APTMS was taken as 1:1.5 (i.e., NCC: NT and APTMS). About 500 mL of acetone was added into a beaker of 1000 mL and loaded with 15 g of NCC. 16.875 g of NT was poured into the same beaker, and stirred with a magnetic stirrer for 10 min, followed by the sonication for 30 min in an ultrasonic bath. Further, simultaneous cycles of magnetic stirring and sonication were employed with the same time interval for the complete exfoliation of the NCC sheet in acetone, as shown in the Figure 1. After sonication, the solution of NCT was centrifuged to recover acetone for the next batch, and the solid NCT was oven-dried at 60 °C for 2 h and stored in a capped container.
[028] Modification of NCT by grafting with APTMS: The synthesized NCT composite was further modified by grafting with APTMS. For the modification, 5.625g of APTMS was taken and diluted in an aqueous alcohol solution of ethanol with a ratio of 95% ethanol and 5% water in a three-necked round bottom flask equipped with a mechanical stirrer, water condenser, and adding funnel in the water bath with temperature control. The pH of the mixture was adjusted to 4–4.5 by adding a few drops of acetic acid as a catalyst under continuous stirring for 1 h at room temperature. The pH of the mixture was maintained at 4 for a complete 1 h; simultaneously, suspension of NCT was prepared. Then, NCT suspension was added continuously in the flask, mixed with the solution by a mechanical stirrer, and refluxed for the next 3 h at 60 °C by the gradual increase in the water bath temperature. After 3 h, the heating was turned off, and the mixture was continuously stirred overnight. The NCT-APTMS solution was then centrifuged to remove the excess APTMS, which did not graft on NCT. The samples (grafted NCT Composite) were freeze-dried for 6 h and stored in a capped container.
[029] Preparation of Hydrophilic coating: 75-90 parts of resin polymer (commercial acrylic resin) was taken in a vessel and stirred with homogeniser. 10-20 parts of solvent was added to the vessel and stirred for 10 min. Then 1-5 parts of grafted NCT composite was added to mixture slowly and mixed further for 30 min to get final product. The composition of the hydrophilic coating is provided in Table 1 as follows:
[030] Table 1
Sr.No. Material Details Ex-1
(parts by weight) Ex-2
(parts by weight) Ex-3
(parts by weight) Ex-4
(parts by weight) Ex-5
(parts by weight)
1 Component A '(NCT Composite) 1.00 2.00 5.00 0.50 10.00
2 Component B (Resin) 89.00 88.00 85.00 89.00 70.00
3 Component C (Solvent) 10.00 10.00 10.00 10.50 20.00

[013] The properties of the hydrophilic coating composition prepared according to present invention was evaluated for wettability, required quick dry time and surface finish and the results are shown in Table 2 as follows:
[014] Table 2
Sr. No. Test Ex-1 Ex-2 Ex-3 Ex-4 Ex-5
1 Appearance whitish coating whitish coating whitish coating whitish coating whitish
coating
2 MEK Rub (with Epoxy base coat) >100 >100 >100 >100 >100
3 Bend Test Pass Pass Pass Pass Pass
4 Cross hatch test Pass Pass Pass Pass Pass
5 Coating surface strains in Erichsen cupping tests >6 Pass >6 Pass >6 Pass >6 Pass >6 Pass
6 Impact Test Pass Pass Pass Pass Pass
7 Accelerated CuSO4 Corrosion Pass Pass Pass Pass Pass
8 Anti Corrosion test (Salt Spay test) (with Epoxy base coat) Pass 1000 Hrs Pass 1000 Hrs Pass 1000 Hrs Pass 1000 Hrs Pass 1000 Hrs
10 Wettability =<10 =<10 =<10 =<50 =<10
12 Wettability after 160 Hr running water 52 48 38 >100 20 (Delamination observed)

[031] As demonstrated above, the hydrophilic coating compositions according to present invention provides the adequate wettability along with the required quick dry time and surface finish. The hydrophilic coating compositions are useful for application on aluminum sheets, preferably for heat exchanger application.
[032] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims. , Claims:We Claim:
1. A coating composition comprising:
- component A selected from NCT composite based on nanocrystalline cellulose (NCC) and nano-TiO2 (NT) which is grafted with 3-aminopropyltrimethoxy silane (APTMS);
- component B selected from a resin polymer; and
- component C selected from a solvent.
2. The coating composition as claimed in claim 1, comprising 1 to 5 parts of component A, 75 to 90 parts of component B and 10 to 20 parts of component C.
3. The coating composition as claimed in claim 1, wherein the nanocrystalline cellulose (NCC) is a spray dried powder with bulk density 04-06 g/cm3 and moisture =<6 %.
4. The coating composition as claimed in claim 1, wherein the nano-TiO2 (NT) has the particle size range 10-40 nm and specific surface area (SSA) 160+/- 30 m2/gram.
5. The coating composition as claimed in claim 1, wherein the resin polymer is an acrylic resin polymer selected from Pidicryl 3539, PRIMAL™ AC-2337 or REVACRYL AE6030.
6. The coating composition as claimed in claim 1, wherein the solvent is selected from water.
7. A process for preparing the coating composition as claimed in claims 1 to 6, comprising the following steps:
a. adsorption of NT on NCC with ultrasonication at room temperature, followed by simultaneous cycles of magnetic stirring and sonication with at a predetermined time interval to achieve a solution of NCT composite,
b. centrifugation of the solution of NCT composite to recover solvent and solid NCT composite,
c. drying the solid NCT composite,
d. modification of solid NCT composite by grafting with APTMS in an aqueous alcohol solution and acid catalyst to provide a NCT suspension,
e. continuous stirring of the NCT suspension at a predetermined pH to provide grafted NCT composite,
f. blending predetermined amounts of the grafted NCT composite, resin polymer and a solvent to provide the hydrophile coating.
8. The process as claimed in claim 7, wherein the ratio of NCC to NT and APTMS was taken as 1:1.5 (NCC: NT and APTMS).
9. The process as claimed in claim 7, wherein the acid catalyst is selected from acetic acid.
10. The process as claimed in claim 7, wherein the predetermined pH is in the range of 4 to 5, preferably 4 to 4.5.
11. A method of coating metal sheet, comprising the following steps:
a) degreasing of a metal sheet with water and drying to remove the residual oil and smut on the sheet;
b) coating the degreased metal sheet with a corrosion protection coating composition using three roller applicator mechanism of appropriate thickness;
c) drying the coated metal sheet in oven for less than 15 sec;
d) cooling the coated metal sheet to room temperature with chilled rolls;
e) coating the sheet obtained in step (d) with the coating composition claimed in claims 1 to 6 with three roller applicator mechanism of appropriate thickness followed by drying to get final dried film coating on the metal sheet.
12. The method as claimed in claim 11, wherein the metal sheet is selected from aluminum or tin.
13. The method as claimed in claim 11, wherein the final dried film coating has a thickness of 0.2 to 0.8 GSM.
14. The method as claimed in claim 11, wherein the drying in oven is between 225 to 265 oC.
15. Use of the coating composition for metal sheets or container, preferably as a hydrophilic organic coating on aluminum sheets for heat exchanger application.
Dated 02nd of February 2024
Hindalco Industries Limited
By their Agent & Attorney

(Nisha Austine)
of Khaitan & Co
Reg No IN/PA-1390