Latex having a high solids content and a low viscosity and exhibiting a bimodal distribution

1. A process for the preparation of a latex by the emulsion polymerization at a temperature of between 30 and 90 C. of at least one ethylenically unsaturated monomer in the presence of at least one surfactant and of a seed of polymer particles with a diameter of between 200 and 450 nm representing from 5 to 25% by weight of the total weight of monomer and seed polymerization being initiated by a mixed water-soluble/fat-soluble system.

2. The process as claimed in claim 1 , characterized in that the seed is introduced before the beginning of the polymerization.

3. The process as claimed in claim 1 , characterized in that the seed is introduced after the beginning of the polymerization and before achieving 80% conversion of the monomers to be polymerized.

4. The process as claimed in claim 1 , characterized in that the seed is introduced in the form of a latex.

5. The process as claimed in claim 1 , characterized in that the seed is introduced in the form of a redispersible powder.

6. The process as claimed in claim 1 , characterized in that the seed is prepared in situ by emulsion polymerization.

7. The process as claimed in claim 1 , characterized in that the seed is composed essentially of (meth)acrylic polymers.

8. The process as claimed in claim 1 , characterized in that the surfactant is chosen from anionic surfactants, selected from alkylaryl ether sulfate or alkyl ether sulfates, or nonionic surfactants.

9. The process as claimed in claim 1 , characterized in that the mixed system is composed of a molar ratio of the water-soluble initiator to the fat-soluble initiator of between 0.01/1 and 1/0.01.

10. The process as claimed in claim 1 , characterized in that the water-soluble initiator is chosen from sodium, potassium and ammonium persulfates, or water-soluble azo derivatives.

11. The process as claimed in claim 1 , characterized in that the fat-soluble initiator is chosen from peroxides and hydroperoxides which are insoluble in water, peroxyesters, peroxydicarbonates or fat-soluble azo derivatives.

12. The process of claim 10 wherein the water-soluble azoderivatives are 4,4′-azobis(4-cyanovaleric acid) or 2,2′-azobis(2-amidinopropane)dihydrochloride.

13. The process of claim 10 further comprising a reducing agent.

14. The process of claim 13 wherein the reducing agent is selected from sodium formaldehydesulfoxylate, sodium metabisulfite or ascorbic acid.

15. The process of claim 10 further comprising an oxidizing agent.

16. The process of claim 15 wherein the oxidizing agent is a hydroperoxide selected from the group consisting of aqueous hydrogen peroxide solution, tert-butyl hydroperoxide, tert-amyl hydroperoxide, cumyl hydroperoxide or the sodium salt of the mixture of n- and p-diisopropylbenzene dihydroperoxide.

17. The process of claim 10 further comprising an activating agent.

18. The process of claim 10 wherein the activating agent is a metal salt selected from iron sulfate, copper sulfate or cobalt acetate.

19. The process of claim 11 wherein the azo derivatives are selected from azobisisobutyronitrile, azobiisobutyrodimethyl ester or azobiisobutyrodienthyl ester.

20. The process of claim 8 wherein the anionic surfactant is selected from alkylaryl ether sulfate or alkyl ether sulfates.

21. The process of claim 8 wherein the nonionic surfactant is selected from ethoxylated alkylphenol or ethoxylated fatty alcohols.

22. A latex obtained by the process as defined in claim 1 .

23. A latex obtained by the process as defined in claim 1 , for use in adhesive applications.

24. A latex according to claim 23 , wherein said adhesive applications comprise: pressure-sensitive adhesives used to stick on labels or floor covering adhesives.