Aqueous coating composition

1. Aqueous coating composition comprising:

a cross-linkable binder resin and a liquid carrier, wherein said cross-linkable binder resin comprises a copolymer A) comprising:

5 to 64% by weight of a reaction product of at least one fatty acid having at least one ethylenic double bond and one hydroxyl group in the molecule with a polyalcohol having a hydroxyl functionality of 2 to 8, wherein the % by weight are relative to the binder solids of copolymer A) and wherein the fatty acid in the reaction product of at least one fatty acid having at least one ethylenic double bond and one hydroxyl group in the molecule with a polyalcohol having a hydroxyl functionality is ricinoleic acid.

2. Aqueous coating composition of claim 1 , wherein the copolymer A) comprises 10 to 50% by weight of the reaction product of at least one fatty acid having at least one ethylenic double bond and one hydroxyl group in the molecule with a polyalcohol having a hydroxyl functionality of 2 to 8, wherein the % by weight are relative to the binder solids of copolymer A).

3. Aqueous coating composition of claim 1 or 2 , wherein copolymer A) has an acid number of at least 10 mg KOH/g solids.

4. Aqueous coating composition of claim 3 , wherein copolymer A) has an acid number of 15 to 80 mg KOH/g solids.

5. Aqueous coating composition of claim 1 , wherein copolymer A) has a hydroxyl number of 50 to 250 mg KOH/g solids and a number average molecular weight Mn of 800 to 8000.

6. Aqueous coating composition of claim 1 , wherein copolymer A) comprises

a) 5 to 64% by weight of the reaction product of ricinoleic acid with a polyalcohol having a hydroxyl functionality of 2 to 8 and

b) 36 to 95% by weight of unsaturated monomers comprising:

b1) at least one hydroxyl-functional unsaturated monomer,

b2) at least one acid-functional unsaturated monomer and

b3) optionally at least one other polymerizable unsaturated monomer different from monomers b1) and b2), wherein the % by weight of a) and b) are adding up to 100%.

7. Aqueous coating composition of claim 1 , wherein copolymer A) comprises

a) 5 to 64% by weight of the reaction product of ricinoleic acid with a polyalcohol having a hydroxyl functionality of 2 to 8,

b1) 0 to 60% by weight of at least one hydroxyalkyl ester with at least one primary or secondary hydroxyl group derived from alpha, beta-ethylenically unsaturated monocarboxylic acids,

b2) 2 to 40% by weight of at least one unsaturated acid functional monomer,

b3.1) 0 to 50% by weight of at least one ester of (meth)acrylic acid with aliphatic monohydric branched or linear as well as cyclic alcohols with 1 to 20 C atoms and

b3.2) 0 to 50% by weight of at least one unsaturated vinyl aromatic monomer, wherein the % by weight of reaction product a) and monomers b1) to b3.2) are adding up to 100%.

8. Aqueous coating composition of claim 1 , wherein the reaction product of at least one fatty acid having at least one ethylenic double bond and one hydroxyl group in the molecule with a polyalcohol having a hydroxyl functionality of 2 to 8 is the triglyceride of ricinoleic acid.

9. Aqueous coating composition of claim 1 , wherein the reaction product of at least one fatty acid having at least one ethylenic double bond and one hydroxyl group in the molecule with a polyalcohol having a hydroxyl functionality of 2 to 8 is castor oil.

10. Aqueous coating composition of claim 1 , wherein the copolymer A) is prepared by polymerizing monomers b1) to b3) in the presence of at least 20% by weight of the total amount of the reaction product of ricinoleic acid with a polyalcohol having a hydroxyl functionality of 2 to 8.

11. Aqueous coating composition of claim 6 , wherein the copolymer A) is a graft copolymer comprising:

8-92% by weight of the graft copolymer of a polymeric backbone of polymerized reaction product a) and monomers b) and further comprising 92-8% by weight of the graft copolymer, of a macromonomer c) attached to said polymeric backbone at a single terminal point of said macromonomer, wherein the % by weight are adding up to 100%, said macromonomer having a number average molecular weight Mn of 500-8000 and comprising 10 to 100% by weight of the macromonomer of ethylenically unsaturated acid-functional and/or amine-functional monomers.

12. Aqueous coating composition of claim 11 , wherein the copolymer A) is prepared by polymerizing monomers b1) to b3) in presence of a mixture of 20 to 80% by weight of the reaction product a) of at least one fatty acid having at least one ethylenic double bond and one hydroxyl group in the molecule with a polyol having a hydroxyl functionality of 2 to 8 and 20 to 80% by weight of macromonomer c), wherein the % by weight are adding up to 100%.

13. Aqueous coating composition of claim 1 , further comprising a cross-linking agent.

14. A process for the preparation of a coating layer, comprising the successive steps:

1) applying a coating layer from a coating composition of claim 1 to a substrate,

2) optionally, flashing off the applied coating layer to remove volatile compounds, and

3) curing the coating layer.

15. The process of claim 14 , wherein the coating layer is selected from the group consisting of a single-layer coating and a coating layer within a multilayer coating.

16. The process of claim 14 or 15 , wherein the coating layer is selected from a group consisting of a clear top coat layer and a pigmented single-stage top coat layer.