Water-absorbing polymer structures produced using polymer dispersions

摘要

The present invention relates to a process for the production of water-absorbing polymer structures, comprising the process steps of providing of an aqueous monomer solution comprising a polymerizable, monoethylenically unsaturated monomer (α1) carrying acid groups or a salt thereof; free-radical polymerization of the aqueous monomer solution to give a polymer gel, drying of the optionally comminuted polymer gel to give water-absorbing polymer structures, and surface post-crosslinking of the optionally ground and sieved water-absorbing polymer structures, wherein a thermoplastic polymer is added to the aqueous monomer solution before process step ii) or during process step ii), preferably before process step ii), or II) the polymer gel after process step ii) and before process step iv) or during process step iv), preferably before process step iv), or III) the water-absorbing polymer structure after process step iv).

主权项

1. A process for producing water-absorbing polymer structures, comprising the process steps of:
i) providing an aqueous monomer solution comprising
from 70 to 98.79 wt % of a polymerizable, monoethylenically unsaturated monomer (α1) bearing acid groups, or a salt thereof,from 0.01 to 2.5 wt % of a crosslinker (α3), andadding from 0.05 to 5 wt % based on the total weight of the monomer solution of a thermoplastic polymer dispersion having a Brookfield viscosity in a range of from 5 to 3,000 mPa·sec, determined at 20° C., to the aqueous monomer solution and wherein the thermoplastic polymer dispersion is a mixture of the thermoplastic polymer and a dispersion agent wherein these two components do not dissolve in one another, ii) free-radically polymerizing the aqueous monomer solution to obtain a polymer gel, iii) comminuting the polymer gel to form comminuted polymer gel, iv) drying the comminuted polymer gel of step iii) to obtain water-absorbing polymer structures, v) grinding and sieving the water-absorbing polymer structures, and vi) surface postcrosslinking the ground and sieved water-absorbing polymer structures of step v), wherein the thermoplastic polymer dispersion is added to the aqueous monomer solution before process step ii) or during process step ii) and wherein the water-absorbing polymer structures do not contain a silicon oxide compound and wherein the water-absorbing polymer structures have the following properties: (β1) a dust content determined by the test method described herein for the entire particle fraction of not more than 1.0% (β2) a flow value determined by the test method described herein for the entire particle fraction of at most about 15; (β3) a retention, as determined according to ERT 441.2-02, of from about 25 g/g to about 35 g/g; (β4) a Gel Bed Permeability, as determined by the test method described herein, of from about 30 darcy to about 150 darcy wherein the value of the Gel Bed Permeability increases from 74.8 darcy to 113.3 darcy when the amount of thermoplastic polymer dispersion is increased from 0.5 wt % to 1.5 wt %; and (β5) at least 50 wt. % based on the total weight of the post crosslinked water-absorbing polymer structures having a particle size in a range of from 300 to 600 μm.