Method for Producing Water-Absorbent Polymer Particles with a Higher Permeability by Polymerising Droplets of a Monomer Solution

Abstract

A process for preparing water-absorbing polymer beads with high permeability by polymerizing droplets of a monomer solution, comprising monomers bearing acid groups, in a gas phase surrounding the droplets, wherein the monomer solution comprises polyvalent cations and the polymer beads have a mean diameter of at least 150 μm.

1 . A process for preparing water-absorbing polymer beads comprising polymerizing droplets of a monomer solution comprising
 a) at least one ethylenically unsaturated monomer bearing acid groups,   b) at least one crosslinker,   c) at least one initiator, and   d) water,   
       in a gas phase surrounding the droplets, wherein the monomer solution comprises polyvalent cations and the polymer beads have a mean diameter of at least 150 μm. 
     
     
         2 . The process according to  claim 1 , wherein the monomer solution comprises from 0.001 to 0.25% by weight of polyvalent cations, based on monomer a). 
     
     
         3 . The process according to  claim 1 , wherein the polyvalent cation is at least trivalent. 
     
     
         4 . The process according to  claim 1 , wherein monomer a) is acrylic acid to an extent of at least 50 mol %. 
     
     
         5 . The process according to  claim 1 , wherein the polymer beads have a mean diameter of at least 200 μm. 
     
     
         6 . The process according to  claim 1 , wherein at least 90% by weight of the polymer beads have a diameter of from 100 to 800 μm. 
     
     
         7 . The process according to  claim 1 , wherein a carrier gas flows through a reaction chamber. 
     
     
         8 . The process according to  claim 7 , wherein the carrier gas leaving the reaction chamber is recycled at least partly after one pass. 
     
     
         9 . The process according to any of  claim 7 , wherein an oxygen content of the carrier gas is from 0.001 to 0.15% by volume. 
     
     
         10 . The process according to  claim 1 , wherein the polymer beads are dried and/or postcrosslinked in at least one further process step. 
     
     
         11 . Water-absorbing polymer beads prepared according to the process of  claim 1 . 
     
     
         12 . 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, and a permeability of at least 5×10−7 cm 3  s/g. 
     
     
         13 . Polymer beads according to  claim 12 , having a centrifuge retention capacity of at least 10 g/g. 
     
     
         14 . Polymer beads according to  claim 12 , having a mean diameter of at least 200 μm. 
     
     
         15 . Polymer beads according to  claim 12 , wherein at least 90%, by weights of the polymer beads have a diameter of from 100 to 800 μm. 
     
     
         16 . Polymer beads according to  claim 12 , comprising at least partly of polymerized ethylenically unsaturated acid-bearing monomers. 
     
     
         17 . Polymer beads according to  claim 16 , wherein the acid groups of the polymerized ethylenically unsaturated monomer are at least partly neutralized. 
     
     
         18 . Polymer beads according to  claim 16 , wherein the ethylenically unsaturated monomer is acrylic acid to an extent of at least 50 mol %. 
     
     
         19 . Polymer beads according to  claim 12 , which comprise polyvalent cations. 
     
     
         20 . (canceled) 
     
     
         21 . A hygiene article comprising polymer beads according to  claim 12 . 
     
     
         22 . A hygiene article comprising polymer beads prepared according to the process of  claim 1 .