Method for producing post-cured water-absorbent polymer particles with a higher absorption by polymerising droplets of a monomer solution
A process for preparing postcrosslinked water-absorbing polymer beads with high absorption by polymerizing droplets of a monomer solution in a gas phase surrounding the droplets, wherein the solids content of the monomer solution is at least 35% by weight and the polymer beads have a mean diameter of at least 150 μm.
1. Water-absorbing polymer beads having a mean sphericity of at least 0.84, a content of hydrophobic solvents of less than 0.005%, by weight, a centrifuge retention capacity (CRC) of at least 20 g/g, and a free swell rate (FSR), which fulfill a condition that
FSR>−0.00082 CRC 2 +0.07 CRC−0.95.
2. Polymer beads according to claim, 1 having a permeability of at least 2×10 −7 cm 3 s/g.
3. Polymer beads according to claim 1 , having a mean diameter of at least 200 μm.
4. Polymer beads according to claim 1 , wherein at least 90%, by weight, of the polymer beads have a diameter of from 100 to 800 μm.
5. Polymer beads according to claim 1 , comprising at least partly of polymerized ethylenically unsaturated acid-bearing monomers.
6. Polymer beads according to claim 5 , wherein the acid groups of the polymerized ethylenically unsaturated monomer have been at least partly neutralized.
7. Polymer beads according to claim 6 , wherein the ethylenically unsaturated monomer is at least 50 mol % acrylic acid.