Superabsorbent polymers with rapid absorption properties and process for producing same

1. A process for producing a water-absorbing polymer composition, comprising process steps of

(i) mixing to form an aqueous monomer solution,

(α1) 0.1 to 99.999% by weight of polymerizable, ethylenically unsaturated monomers containing acid groups; salts of polymerizable, ethylenically unsaturated monomers containing acid groups; salts of polymerizable, ethylenically unsaturated monomers comprising a protonated nitrogen; polymerizable, ethylenically unsaturated monomers comprising a quaternized nitrogen; or mixtures thereof,

(α2) 0 to 70% by weight of polymerizable, ethylenically unsaturated monomers copolymerizable with the monomers provided in (α1),

(α3) 0.001 to 10% by weight of one or more crosslinkers,

(α4) 0 to 30% by weight of water-soluble polymers, and

(α5) 0 to 20% by weight of one or more assistants, where and wherein the sum of the weights of the compounds recited in (α1) to (α5) is 100% by weight,

(ii) adding an initiator and then free-radical polymerizing with crosslinking of the compounds recited in (α1) to (α4) to form a water-insoluble, aqueous untreated hydrogel polymer,

(iii) drying the water-insoluble, aqueous untreated hydrogel polymer to form a dried hydrogel polymer,

(iv) grinding and sieving the dried hydrogel polymer to form a ground and sieved hydrogel polymer,

(v) surface postcrosslinking the ground and sieved hydrogel polymer to provide a water-absorbing polymer and

(vi) drying the water-absorbing polymer, wherein prior to addition of the initiator and the commencement of free-radical polymerization, the aqueous monomer solution is admixed with 0.07 to 1% by weight, based on the weight of the water-absorbing polymer formed from the aqueous monomer solution, of a blowing agent having a particle size of 10 μm to 900 μm, and 0.07 to 1% by weight, based on the weight of the water-absorbing polymer formed from the aqueous monomer solution, of at least one surfactant which is a nonionic unsaturated polyether copolymer comprising at least one terminal functionality which is a methallyl ether group having the following formula:

in which the alkylene glycol units C 2 H 4 O and C q H 2q O are arranged randomly, in blocks or as a gradient, R 1 is —CH 3 , R 2 is a carbonyl group C═O and R 3 is —H or a linear or branched C 1− to C 7 -alkyl, C 6 - to C 9 -alkylaryl or C 1- to C 7 -acyl radical, q is a number from 3 to 4, and n and m are each a number from 1 to 20, or

in which the alkylene glycol units C 2 H 4 O and C q H 2q O are arranged randomly or as a gradient, R 1 is —CH 3 , R 2 is an alkylene group from the group of methylene or ethylene, and R 3 is —H or a linear or branched C 1- to C 7 -alkyl, C 6 - to C 9 -alkylaryl or C 1- to C 7 -acyl radical, q is a number from 3 to 4, and n and m are each a number from 1 to 20.

2. The process according to claim 1 , wherein at least one surfactant and the blowing agent are added together to the aqueous monomer solution.

3. The process according to claim 1 , wherein the blowing agent consists of a powder of inorganic particles.

4. The process according to claim 1 , wherein the blowing agent consists of sodium carbonate particles.

5. The process according to claim 1 , wherein more than 35% by weight of the blowing agent has a particle size of 100-300 μm.

6. The process according to claim 1 , wherein a water-absorbing polymer prepared therefrom has a free swell rate within the range from 0.30 to 0.70.

7. The process according to claim 1 , wherein a water-absorbing polymer prepared therefrom has a surface tension (ST) is in the range above 50 mN/m.

8. The process according to claim 1 , wherein a water-absorbing polymer having a starting weight of 1.5 grams prepared therefrom has a permeability as determined by the measurement of saline flow conductivity is in the range from 30 to 200.

9. A water-absorbing polymer obtainable according to claim 1 .

10. A composite including a water-absorbing polymer according to claim 9 .

11. A process for producing a composite, wherein a water-absorbing polymer according to claim 9 and an assistant are contacted with one another.

12. A composite obtainable by a process according to claim 11 .

13. A process for producing a hydrogel polymer, comprising process steps of

(i) mixing to form an aqueous monomer solution,

(α1) 0.1 to 99.999% by weight of polymerizable, ethylenically unsaturated monomers containing acid groups; salts thereof of polymerizable, ethylenically unsaturated monomers containing acid groups; salts of polymerizable, ethylenically unsaturated monomers comprising a protonated nitrogen; or polymerizable, ethylenically unsaturated monomers including comprising a quaternized nitrogen; or mixtures thereof,

(α2) 0 to 70% by weight of polymerizable, ethylenically unsaturated monomers copolymerizable with the monomers provided in (α1)

(α3) 0.001 to 10% by weight of one or more crosslinkers,

(α4) 0 to 30% by weight of water-soluble polymers,

(α5) 0 to 20% by weight of one or more assistants, and wherein the sum of the weights of the compounds recited in (α1) to (α5) is 100% by weight,

(ii)adding an initiator and then free-radical polymerizing with crosslinking of the compounds recited in (α1) to (α4) to form a water-insoluble, aqueous untreated hydrogel polymer,

(iii) drying the water-insoluble, aqueous untreated hydrogel polymer to form a dried hydrogel polymer,

(iv) grinding and sieving the dried hydrogel polymer to form a ground and sieved hydrogel polymer, wherein

the aqueous monomer solution, prior to addition of the initiator and the commencement of free-radical polymerization, is admixed with 0.07 to 1% by weight based on the weight of the ground and sieved hydrogel polymer formed from the aqueous monomer solution of at least one surfactant which is a nonionic unsaturated polyether copolymer comprising at least one terminal functionality which is a methallyl ether group and 0.07 to 1% by weight, based on the weight of the ground and sieved hydrogel polymer formed from the aqueous monomer solution, of a blowing agent having a particle size of 10 μm to 900 μm.