Method for producing water-absorbent polymer particles with a higher permeability by polymerizing droplets of a monomer solution

Abstract

A process for preparing water-absorbing polymer beads with high permeability by polymerizing droplets of a monomer solution in a gas phase surrounding the droplets, wherein a water-insoluble inorganic salt is suspended in the monomer solution 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,   b) at least one crosslinker,   c) at least one initiator, and   d) water,   
       in a gas phase surrounding the droplets, wherein a water-insoluble inorganic salt is suspended in the monomer solution and the polymer beads have a mean diameter of at least 150 μm. 
     
     
         2 . The process according to  claim 1 , wherein the monomer a) has at least one acid group. 
     
     
         3 . The process according to  claim 2 , wherein the acid groups of the monomer a) are at least partly neutralized. 
     
     
         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  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 - 21 . (canceled) 
     
     
         22 . A hygiene article comprising polymer beads prepared according to the process of  claim 1 .