Aqueous dispersions

1. An aqueous dispersion obtained by a process comprising the steps of:

(a) preparing an acidic copolymer (A) having an acid value when contacted with water of at least 140 mg KOH/g by radical copolymerization of monomers comprising:

(a1) at least one unsaturated fatty acid,

(a2) at least one ethylenically unsaturated monomer containing at least one acid group or group capable of forming an acid group when contacted with water, and

(a3) at least one other ethylenically unsaturated monomer different from (a1) and (a2), wherein the at least one unsaturated fatty acid (a1) is incorporated in the polymeric backbone of the acid copolymer (A) via carbon-carbon bonds,

(b) neutralizing totally or partially the acid groups of copolymer (A) and dissolving it in water to form a totally or partially neutralized copolymer (A), and

(c) copolymerizing in the solution obtained at step (b) at least one monomer mixture different from the monomer mixture of step (a) to form a copolymer (B).

2. The aqueous dispersion according to claim 1 , wherein copolymer (A) is obtained from:

5 to 50 wt % of unsaturated fatty acid (a1),

5 to 90 wt % of ethylenically unsaturated monomer (a2),

5 to 80 wt % of ethylenically unsaturated monomer (a3),

based on the sum of (a1), (a2) and (a3).

3. The aqueous dispersion according to claim 1 , wherein the at least one unsaturated fatty acid (a1) is selected from the group consisting of soybean oil fatty acids, linseed oil fatty acids, tall oil fatty acids and mixtures thereof.

4. The aqueous dispersion according to claim 1 , wherein the at least one ethylenically unsaturated monomer (a2) is selected from the group consisting of (meth)acrylic acid, crotonic acid and mixtures thereof.

5. The aqueous dispersion according to claim 1 , wherein at least one ethylenically unsaturated monomer (a3) used in step (a) has a glass transition temperature of its homopolymerisate of higher than 50° C.

6. The aqueous dispersion according to claim 1 , wherein the at least one ethylenically unsaturated monomer (a3) used in step (a) is selected from the group consisting of styrene, alpha-methylstyrene, (meth)acrylamide, diacetone (meth)acrylamide, isobornyl (meth)acrylate, methyl methacrylate, and mixtures thereof.

7. The aqueous dispersion according to claim 1 , wherein the totally or partially neutralized copolymer (A) has a degree of neutralization of at least 30% based on the total number of acid groups present in copolymer (A) when contacted with water and/or wherein the copolymer (A) is neutralized with at least one neutralizing agent selected from the group consisting of ammonia, amines and inorganic hydroxides.

8. The aqueous dispersion according to claim 1 , wherein the copolymer (B) is obtained from monomers selected from the group consisting of styrene, vinyltoluene, alpha-methyl styrene, ethyl styrene, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, glycidyl (meth)acrylate, diacetone (meth)acrylamide, acetoacetoxyethyl(meth)acrylate, ureido(meth)acrylate and mixtures thereof.

9. The aqueous dispersion according to claim 1 , wherein the copolymer (B) has at least two glass transition temperatures.

10. The aqueous dispersion according to claim 1 comprising:

from 10 wt % to 40 wt % of copolymer (A),

from 60 wt % to 90 wt % of copolymer (B),

based on the sum of (A) and (B).

11. The aqueous dispersion according to claim 1 subject to crosslinking reactions due to the presence of binding sites present in copolymer (A) and/or copolymer (B) and in external compounds.

12. A process for the preparation of the aqueous dispersion according to claim 1 , the process comprising the steps of:

(a) preparing an acidic copolymer (A) having an acid value when contacted with water of at least 140 mg KOH/g by radical copolymerization of monomers comprising:

(a1) at least one unsaturated fatty acid,

(a2) at least one ethylenically unsaturated monomer containing at least one acid group or group capable of forming an acid group when contacted with water, and

(a3) at least one other ethylenically unsaturated monomer different from (a1) and (a2), wherein the at least one unsaturated fatty acid (a1) is incorporated in the polymeric backbone of the acid copolymer (A) via carbon-carbon bonds,

(b) neutralizing totally or partially the acid groups of copolymer (A) and dissolving it in water to form a totally or partially neutralized copolymer (A), and

(c) copolymerizing in the solution obtained at step (b) at least one monomer mixture different from the monomer mixture of step (a) to form a copolymer (B).

13. A blend comprising the aqueous dispersion according to claim 1 and at least one further binder composition.

14. The blend according to claim 13 , wherein the at least one further binder composition is an alkyd resin or a polyurethane dispersion.

15. The blend according to claim 13 wherein the at least one further binder comprises an oxidatively drying alkyd resin and wherein the amount of said alkyd resin is from 60 to 95 wt % based on the total amount of copolymer (A), copolymer (B) and said alkyd resin.

16. The blend according to claim 15 wherein the alkyd resin is selected from the group consisting of acrylic modified alkyd resins, urethane modified alkyd resins and alkyd-polyurethanes hydrids comprising moieties from acrylic modified alkyd resins.

17. The blend according to claim 15 containing less than 1 wt % of siccative.

18. A process for preparing a coated substrate or article, comprising a step of coating at least part of a surface of the substrate or article with the aqueous dispersion according to claim 11 .

19. A process for preparing a coated substrate or article, comprising a step of coating at least part of a surface of the substrate or article with the blend according to claim 13 .