Method for producing a prefabricated building material

1. An aqueous alkyl ketene dimer dispersion comprising

(a) an alkyl ketene dimer of the formula (I)

and/or of the formula (II)

in which

R 1 and R 2 are identical or different hydrocarbon radicals comprising 10 to 24 carbon atoms;

(b) at least one emulsifier having a nitrogen content in the range from 0.05 to 1% by weight and a Brookfield viscosity (20° C.; spindle 61 or 62; 12 rpm) in the range from about 10 to about 500 mPas in a 10% w/w aqueous solution, the emulsifier being selected from the group consisting of a starch, cellulose, starch derivative and cellulose derivative;

(c) a condensation product of phenol sulfonic acid and formaldehyde, naphthalene sulfonic acid and formaldehyde or naphthalene sulfonic acid, phenol, formaldehyde and urea wherein sulfonic acid groups of the phenol sulfonic acid and the naphthalene sulfonic acid may optionally be present in protonated or deprotonated or partly in protonated and partly in deprotonated form;

wherein the dispersion has a charge density in the range from −5 to −150 μeq/g.

2. The dispersion of claim 1 having a charge density in the range from −10 to −120 μeq/g.

3. The dispersion of claim 1 , wherein the at least one emulsifier has a nitrogen content in the range from 0.2 to 0.8% by weight.

4. The dispersion of claim 1 , which additionally comprises at least one fatty alcohol alkoxylate, fatty amine alkoxylate or fatty acid alkoxylate.

5. The dispersion of claim 4 , wherein the fatty alcohol alkoxylate is a C 8 -C 18 alkanol ethoxylate with 10 to 30 ethylene oxide groups.

6. The dispersion of claim 1 , which additionally comprises a wax.

7. The dispersion of claim 1 , in the form of a gypsum composition which dispersion additionally comprises gypsum hemihydrate or anhydrite or a mixture thereof.

8. The dispersion of claim 7 , wherein the gypsum hemihydrate or anhydrite is selected from α-hemihydrate, α/β-hemihydrate, β-hemihydrate, natural anhydrite, synthetic anhydrite, anhydrite obtained from flue gas desulfurization, and/or mixtures of two or more thereof.

9. The dispersion of claim 7 , which additionally comprises an aqueous foam.

10. The dispersion of claim 9 , wherein a foam having a density from about 50 to 300 g/l is used.

11. The dispersion of claim 10 , wherein the foam is obtained from 0.01 to 2 g surfactant per kg gypsum hemihydrate or anhydrite.

12. A method for producing a gypsum-containing foamed prefabricated building material comprising the steps of

(a) providing the dispersion in the form of a gypsum composition additionally comprising an aqueous foam as defined in claim 9 ; and

(b) forming, optionally curing and drying the gypsum composition to obtain the foamed prefabricated building material.

13. The method of claim 12 , wherein the gypsum composition is obtained by adding the alkylketene dimer of the formula (I) or (II) to components (b) and (c) of the dispersion and then adding the foam.

14. The method of claim 13 , wherein the alkyl ketene dimer is employed in the form of an aqueous dispersion.

15. The method of claim 14 , wherein the aqueous alkyl ketene dispersion comprises 1 to 60 wt % of ketene dimer, based on the total weight of the dispersion.

16. The method of claim 12 , wherein 0.02 to 8.0 wt %, of the alkyl ketene dimer, based on the weight of the gypsum hemihydrate or anhydrite, is used.

17. A prefabricated construction chemical building material comprising a gypsum body hydrophobized with the dispersion of claim 7 .

18. A gypsum-containing prefabricated building material obtained from the dispersion according to claim 7 .

19. The building material of claim 17 wherein the gypsum body has a core density of 0.4 to 1.1 kg/dm 3 .

20. The building material of claim 17 selected from gypsum plasterboard panels, gypsum fiberboard panels, gypsum-containing wallboarding panels, and gypsum-containing moldings.

21. A gypsum-containing foamed prefabricated building material, comprising a gypsum body hydrophobized with the dispersion of claim 9 .