Method for the wet drawing of steel cables for reinforcing tires

1. A process for the wet drawing of a steel wire intended for reinforcing a pneumatic tire, said process comprising the steps of:

starting from a steel wire having a diameter greater than 0.6 mm; and

drawing said wire through a series of dies of decreasing diameter, in the presence of a lubricant composition that is in the form of an aqueous dispersion, down to a predetermined final diameter of less than 0.5 mm,

wherein said aqueous dispersion comprises solid particles of an ester of a fatty acid comprising from 5 to 40 carbon atoms,

wherein the fatty acid ester corresponds to the formula:

[R—COO—] x —A—[OH] y   (I)

in which R is a linear or branched, saturated or unsaturated hydrocarbon group, A is a hydrocarbon group, optionally interrupted by one or more heteroatoms, of valency x+y, x is an average number from 1 to 5, y is an average number from 0 to 5, and x+y varies from 1 to 10;

wherein the ester is a diester corresponding to the formula:

R 1 —CO—O—A—O—CO—R 2   (II)

in which R 1 and R 2 , which are identical or different, are linear or branched, saturated or unsaturated hydrocarbon groups comprising from 4 to 39 carbon atoms; and

wherein R 1 and R 2 comprise from 13 to 21 carbon atoms.

2. The process according to claim 1 , wherein the fatty acid comprises from 6 to 24 carbon atoms,

3. The process according to claim 2 , wherein the fatty acid comprises from 14 to 22 carbon atoms.

4. The process according to claim 1 , wherein the fatty acid ester derives from a diol or from a polyol.

5. The process according to claim 1 , wherein R 1 and R 2 comprise from 15 to 21 carbon atoms.

6. The process according to claim 1 , wherein the divalent group A corresponds to the formula:

—(CH 2 ) z —[EO] m —[PO] m —(CH 2 ) z′ —

in which:

z and z′, which are identical or different, are integers from 1 to 10;

EO is an optional ethylene oxide group;

PO is an optional propylene oxide group;

m and m′, which are identical or different, are average numbers within a range from 0 to 100.

7. The process according to claim 1 , wherein the diester corresponds to the formula:

R 1 —CO—O—(CH 2 ) z″ —O—CO—R 2   (III)

in which z″ is an integer from 1 to 10.

8. The process according to claim 1 , wherein the diester corresponds to the formula:

H 3 C—(CH 2 ) n —CO—O—(CH 2 ) z″ —O—CO—(CH 2 ) n′ —CH 3   (IV)

in which:

z″ is an integer from 1 to 4;

n and n′, which are identical or different, are integers from 14 to 20.

9. The process according to claim 1 , wherein A is an alkylene chosen from the group formed by methylene, ethylene, propylene and butylene groups and mixtures of these groups.

10. The process according to claim 8 , wherein the diester is the ethylene glycol distearate of formula:

H 3 C—(CH 2 ) 16 —CO—O—(CH 2 ) 2 —O—CO—(CH 2 ) 16 —CH 3   (V).

11. The process according to claim 1 , wherein the aqueous dispersion comprises between 0.05 and 6% of ester particles (% by weight).

12. The process according to claim 1 , wherein the ester particles have a particle size distribution with at least 90 wt % of the particles having a size between 0.1 and 50 μm.

13. The process according to claim 1 , wherein the aqueous dispersion further comprises an amphiphilic compound.

14. The process according to claim 13 , wherein the amphiphilic compound is a surfactant.

15. The process according to claim 14 , wherein the surfactant is chosen from the group formed by anionic, cationic, amphoteric, zwitterionic and non-ionic surfactants and mixtures of such surfactants.

16. The process according to claim 15 , wherein the surfactant is a non-ionic surfactant.

17. The process according to claim 16 , wherein the non-ionic surfactant is chosen from the group formed by polyalkoxylated phenols, optionally polyalkoxylated C 6 -C 22 fatty acids or alcohols, polyalkoxylated sorbitan esters, polyoxyalkylenated block polymers and mixtures of such compounds.

18. The process according to claim 17 , wherein the surfactant is chosen from the group formed by ethylene oxide/C 3 -C 10 alkylene oxide block copolymers, ethoxylated or propoxylated di- or tri-styrylphenols, fatty amines and mixtures of such compounds.

19. The process according to claim 18 , wherein the surfactant is an ethylene oxide/C 3 -C 10 alkylene oxide block copolymer.

20. The process according to claim 19 , wherein the surfactant is a polyoxyethylene/polyoxypropylene block copolymer.

21. The process according to claim 20 , wherein the block copolymer is a copolymer of structure [EO] p —[PO] p″ —[EO] p′ , where:

EO is an ethylene oxide group; p and p′, which are identical or different, are average numbers within a range from 2 to 1000; and

PO is an optional propylene oxide group; p″ is an average number within a range from 2 to 1000.

22. The process according to claim 13 , wherein the weight ratio of the amphiphilic compound to the ester particles is between 1/100 and 10/100.

23. The process according to claim 1 , wherein the aqueous dispersion further comprises an extreme pressure additive.

24. The process according to claim 23 , wherein the extreme pressure additiveis chosen from the group formed by phosphate esters, phosphonates, sulphates, (poly)sulphides and mixtures of these compounds.

25. The process according to claim 24 , wherein the extreme pressure additive is a phosphate ester.

26. The process according to claim 23 , wherein the aqueous dispersion comprises between 0.01% and 5% of the extreme pressure additive (% by weight).