Carboxy-functional dimer fatty acid-based reaction products and aqueous basecoat materials comprising said products

1. A pigmented aqueous basecoat material, comprising:

a carboxy-functional dimer fatty acid-based reaction product which is produced by reaction of

(a) at least on dimer fatty acid with

(b) at least one compound of the general structural formula (I):

wherein:

R is a C 3 to C 6 alkylene radical;

n is selected such that the compound (b) possesses a number-average molecular weight of 120 to 6000 g/mol;

components (a) and (b) are used in a molar ratio of at least 1/1; and

the reaction product possesses a number-average molecular weight of 1000 to 20 000 g/mol and an acid number of 10 to 120 mg KOH/g.

2. The basecoat material as claimed in claim 1 , wherein the dimer fatty acid comprises at least 90 wt % of dimeric molecules, less than 5 wt % of trimeric molecules, and less than 5 wt % of monomeric molecules.

3. The basecoat material as claimed in claim 1 , wherein the compound (b) possesses a number-average molecular weight of 180 to 2500 g/mol.

4. The basecoat material as claimed in claim 1 , wherein the group R in the general structural formula (I) comprises tetramethylene radicals.

5. The basecoat material as claimed in claim 1 , wherein components (a) and (b) are used in a molar ratio of 1.1/1 to 3/1.

6. The basecoat material as claimed in claim 1 , wherein the reaction product possesses a number-average molecular weight of 2500 to 10 000 g/mol.

7. The basecoat material as claimed in claim 1 , wherein the reaction product possesses an acid number of 12 to 80 mg KOH/g.

8. The basecoat material as claimed in claim 1 , wherein the components (a) and (b) are used in a molar ratio of 1.2/1 to 2/1.

9. The pigmented aqueous basecoat material as claimed in claim 1 , wherein the sum total of the weight-percentage fractions, based on the total weight of the pigmented aqueous basecoat material, of all the dimer fatty acid-based reaction products is 0.1 to 30 wt %.

10. The pigmented aqueous basecoat material as claimed in claim 1 , further comprising a polyurethane resin that is grafted by olefinically unsaturated monomers and comprises hydroxyl groups, and a melamine resin.

11. A carboxy-functional dimer fatty acid-based reaction product which is produced by reaction of

(a) at least one dimer fatty acids with

(b) at least one compound of the general structural formula (I):

wherein:

R is a C 3 to C 6 alkylene radical;

n is selected accordingly such that the polyether (b) possesses a number-average molecular weight of 120 to 6000 g/mol;

components (a) and (b) are used in a molar ratio of at least 1/1; and

the resulting reaction product possesses a number-average molecular weight of 1000 to 20 000 g/mol and an acid number of 10 to 120 mg KOH/g.

12. A pigmented aqueous basecoat material, comprising:

the reaction product of claim 11 ,

wherein the pigmented aqueous basecoat material is adapted to function as a basecoat material for improving the stability with respect to optical defects in paint systems.

13. A method for producing a multicoat paint system, the method comprising:

(1) applying the pigmented aqueous basecoat material of claim 1 to a substrate,

(2) forming a polymer film from the basecoat material applied in stage (1),

(3) applying a clearcoat material to the polymer film, and then

(4) curing the polymer film together with the clearcoat film.

14. The method as claimed in claim 13 , wherein the substrate is a metallic substrate coated with a cured electrocoat film, and all of the films applied to the electrocoat film are cured jointly.

15. A multicoat paint system produced by the method of claim 13 .

16. A method for improving stability with respect to optical defects in a paint system, the method comprising:

applying a pigmented aqueous basecoat material comprising the reaction product of claim 11 to a surface to form a basecoat; and

painting a surface of the basecoat.