Method for producing hydrophilic, aliphatic polyurethane foams having a low bulk density

1. A method for producing hydrophilic aliphatic polyurethane foam which comprises

I) preparing a mixture of an isocyanate-functional prepolymer A) and a low molecular weight aliphatic diisocyanate A1), wherein the low molecular weight aliphatic diisocyanate A1) has a molar mass of 140 to 278 g/mol

by reacting

the low molecular weight aliphatic diisocyanate A1) with

a di- to hexafunctional polyalkylene oxide A2) having an OH number of 22.5 to 112 mg KOH/g and an ethylene oxide fraction of 50 to 100 mol %, based on the total amount of oxyalkylene groups present,

the ratio of the low molecular weight aliphatic diisocyanate A1) to the di- to hexafunctional polyalkylene oxide A2) being set such that the free low molecular weight aliphatic diisocyanate A1) content in the mixture of the isocyanate-functional prepolymer A) and the low molecular weight aliphatic diisocyanate A1) is 2 to 15 weight %,

II) mixing the mixture of the isocyanate-functional prepolymer A) and the low molecular weight aliphatic diisocyanate A1) with C8- to C22-monocarboxylic acid or their ammonium or alkali metal salt or C12- to C44-dicarboxylic acid or their ammonium or alkali metal salt B) and water C), to prepare a mixture of step II) and

III) foaming and curing the mixture of step II).

2. The method of claim 1 , wherein in step I) the ratio of the low molecular weight aliphatic diisocyanate A1) to the di- to hexafunctional polyalkylene oxide A2) is set such that the free low molecular weight aliphatic diisocyanate A1) content in the resulting mixture of step I) is 2 to 10 weight %.

3. The method of claim 1 , wherein in step I) the ratio of the low molecular weight aliphatic diisocyanate A1) to the di- to hexafunctional polyalkylene oxide A2) is set such that the free low molecular weight aliphatic diisocyanate A1) content in the resulting mixture of step I) is 2 to 8 weight %.

4. The method of claim 1 , wherein the NCO content, determined to DIN-EN ISO 11909, of the mixture of isocyanate-functional prepolymer A) and low molecular weight aliphatic diisocyanate A1) after complete reaction of the OH groups of A2) is 4 to 10 weight %.

5. The method of claim 1 , wherein the low molecular weight aliphatic diisocyanate A1) is hexamethylene diisocyanate, isophorone diisocyanate or a mixture thereof.

6. The method of claim 1 , wherein the di- to hexafunctional polyalkylene oxide A2) is a copolymer of ethylene oxide and propylene oxide having an ethylene oxide content, based on the total amount of oxyalkylene groups present, of 60 to 85 mol %.

7. The method of claim 1 , wherein the di- to hexafunctional polyalkylene oxide A2) has a number-average molecular weight of 3000 to 8500 g/mol.

8. The method of claim 1 , wherein the di- to hexafunctional polyalkylene oxide A2) has a OH functionality of 3 to 4.

9. The method of claim 1 , wherein the mixture of step II) contains a catalyst D), a surfactant E), an alcohol F) and/or a blowing agent G) other than water.

10. The method of claim 9 , wherein

100 parts by weight of the mixture of the isocyanate-functional prepolymer A) and the low molecular weight aliphatic diisocyanate A1),

0.1 to 5 parts by weight of C8- to C22-monocarboxylic acid or their ammonium or alkali metal salt or C12- to C44-dicarboxylic acid or their ammonium or alkali metal salt B),

1 to 200 parts by weight of water C),

0 to 1 part by weight of catalyst D),

0 to 10 parts by weight of surfactant E), and

0 to 20 parts by weight of alcohol F), are provided.

11. The method of claim 1 , wherein the hydrophilic aliphatic polyurethane foam on completion of foaming is heated to speed curing.

12. The method of claim 11 , wherein the hydrophilic aliphatic polyurethane foam on completion of foaming is heated to a temperature of 40 to 140° C.

13. The method of claim 11 , wherein the hydrophilic aliphatic polyurethane foam on completion of foaming is heated to a temperature of 60 to 110° C.

14. A hydrophilic aliphatic polyurethane foam obtained by the method of claim 1 .

15. The hydrophilic aliphatic polyurethane foam of claim 14 , wherein the foam is a wound dressing, an incontinence product or a cosmetic article.

16. A method of preparing a composition for treating wounds comprising utilizing the hydrophilic aliphatic polyurethane foam of claim 14 .

17. The method of claim 1 , wherein the hydrophilic aliphatic polyurethane foam has a bulk density of less than 100 g/l.