Aqueous crosslinkable coating composition

1. A one-pack aqueous coating composition comprising dispersed particles of carbonyl functional vinyl polymer(s), wherein the coating composition further comprises carbodihydrazide, whereby

(i) the equivalent molar ratio of hydrazide groups to carbonyl groups is from 0.1 to 0.95,

(ii) the ratio of number-average molecular weight of the carbonyl functional vinyl polymer(s) to acid value of the carbonyl functional vinyl polymer(s) is higher than 400, and

(iii) the acid value of the carbonyl functional vinyl polymer(s) is from 2 to 100 mg KOH/gram carbonyl functional vinyl polymer.

2. The coating composition according to claim 1 , wherein the equivalent molar ratio of hydrazide groups to carbonyl groups is from 0.2 to 0.95.

3. The coating composition according to claim 1 , wherein the ratio of number-average molecular weight of the carbonyl functional vinyl polymer(s) to acid value of the carbonyl functional vinyl polymer(s) is higher than 600.

4. The coating composition according to claim 1 , wherein the coating composition comprises carbodihydrazide in an amount of less than 3 wt. % and higher than 0.5 wt. %, relative to the total amount of monomers charged for the preparation of the carbonyl functional vinyl polymer(s).

5. The coating composition according to claim 1 , wherein the redox potential of the aqueous colloidal dispersion of the carbonyl functional vinyl polymer(s) prior to the addition of the carbodihydrazide is <+90 mV at pH 7.

6. The coating composition according to claim 1 , wherein the redox potential of the coating composition after addition of the carbodihydrazide is <+32.5 mV at pH 7.

7. The coating composition according to claim 1 , wherein the particles of carbonyl functional vinyl polymer(s) are obtained by emulsion polymerisation.

8. The coating composition according to claim 1 , wherein the particles of carbonyl functional vinyl polymer(s) are obtained by emulsion polymerisation of a monomer mixture comprising carbonyl functional olefinically unsaturated monomer(s), carboxylic acid functional olefinically unsaturated monomer(s) and other olefinically unsaturated monomer(s) to form a copolymer, optionally neutralizing the copolymer with base, and adjusting the pH to a value of at least 6.8.

9. The coating composition according to claim 1 , wherein the pH of the coating composition is above 7.

10. The coating composition according to claim 1 , wherein the particles of carbonyl functional vinyl polymer(s) are ketone functional vinyl polymer particles.

11. The coating composition according to claim 8 , wherein the carbonyl group containing olefinically unsaturated monomers is diacetone acrylamide.

12. The coating composition according to claim 8 , wherein the carboxylic acid functional olefinically unsaturated monomer(s) is methacrylic acid and/or acrylic acid.

13. The coating composition according to claim 1 , wherein the carbonyl functional vinyl polymer is a copolymerization reaction product of a monomer mixture comprising from 70 to 98 weight % of styrene, acrylonitrile and/or alkyl(meth)acrylate monomers where the alkyl has a chain length of 1-11 carbons, based on the total amount of monomers used to prepare the carbonyl functional vinyl polymer.

14. The coating composition according to claim 1 , wherein the carbonyl functional vinyl polymer is a copolymerization reaction product of a monomer mixture consisting of (i) diacetone acrylamide, (ii) (meth)acrylic acid and/or betacarboxyethylacrylate, (iii) styrene, acrylonitrile and/or alkyl(meth)acrylate monomers where the alkyl has a chain length of 1-11 carbons and (iv) optionally other monomers, where the total amount of other monomers is less than 5 weight %, based on the total amount of monomers used to prepare the carbonyl functional vinyl polymer.

15. The coating composition according to claim 1 , wherein the carbonyl functional vinyl polymer(s) have an average glass transition temperature which is in a range of from 5 to 60° C.

16. The coating composition according to claim 1 , wherein the coating composition comprises from 0.1 to 8 wt. % of a surfactant based on total amount of monomers charged for the preparation of the carbonyl functional vinyl polymer(s).

17. A method for preparing the one-pack aqueous coating composition according to claim 1 , the method comprising mixing the carbodihydrazide and the aqueous colloidal polymeric dispersion, to thereby obtain the one-pack aqueous coating composition having an equivalent molar ratio of hydrazide groups to carbonyl groups from 0.1 to 0.95, the ratio of number-average molecular weight of the carbonyl functional vinyl polymer(s) to acid value of the carbonyl functional vinyl polymer(s) of higher than 400, and the acid value of the carbonyl functional vinyl polymer(s) from 2 to 100 mg KOH/gram carbonyl functional vinyl polymer.

18. A method of coating a substrate, wherein the which method comprises:

(i) applying the one-pack aqueous coating composition according to claim 1 to a substrate to form a coating thereof on the substrate,

(ii) causing or allowing an aqueous carrier medium of the composition to be removed, and

(iii) developing crosslinking of the coating applied to the substrate.

19. The method according to claim 18 , wherein step (i) comprises applying the one-pack aqueous coating composition by printing.

20. A crosslinked coating obtained by:

(i) applying the one-pack aqueous coating composition according to claim 1 to a substrate to form a coating thereof on the substrate,

(ii) causing or allowing an aqueous carrier medium of the composition to be removed, and

(iii) forming the cross-linked coating by developing crosslinking of the coating applied to the substrate.

21. The cross-linked coating according to claim 20 , wherein the substrate is selected from the group consisting of:

a) plastic films selected from polypropylene, polyethylene, polyester, polyamide, PVC, polycarbonate, polystyrene, polyurethane, PET, biaxially oriented polypropylene and biaxially oriented PET plastic films,

b) leather, artificial leather, woven and non-woven fabrics of natural or synthetic materials, such as cotton, wool and rayon,

c) metal substrates,

d) wood,

e) paper, and

g) a combination of a), b), c), d) and/or e).

22. The cross-linked coating according to claim 20 , wherein the coating is an overprint varnish or an ink.