Anti-stick processing aids and use thereof in the production of water-absorbing particles

1. A process for producing a water-absorbing polymer in an apparatus, comprising the steps of

(i) mixing

(α1) from 0.1 to 99.999% by weight of polymerizable, ethylenically unsaturated monomers containing acid groups, or salts thereof,

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

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

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

(α5) from 0 to 80% by weight of water, and

(α6) from 0 to 20% by weight of one or more assistants, where the sum of the weights of (α1) to (α5) is 100% by weight,

(ii) free-radical polymerization with crosslinking to form an untreated water-absorbing polymer,

(iii) drying the untreated water-absorbing polymer,

(iv) grinding and sieving the untreated water-absorbing polymer to size,

(v) surface postcrosslinking the ground and sieved untreated water-absorbing polymer and

(vi) finishing the water-absorbing polymer,

wherein an anti-stick processing aid is added either alone or in mixtures before and/or during the drying of the untreated water-absorbing polymer in step (iii) such that the anti-stick processing aid is added before step (iii) to the apparatus used subsequent to step (ii);

wherein the anti-stick processing aid is applied by spraying, jetting, painting, brushing or coating onto drying plates, belts, trays or other receptacles coming into contact with a hydrogel polymer; wherein said drying plates, belts, trays or other receptacles are made of metal and have a metallic surface; wherein the anti-stick processing aid is a non-permanent anti-stick processing aid;

wherein the surface tension of the resulting water-absorbing polymer is between 69.9 and 80 mN/m and, wherein the Centrifuge Retention Capacity (CRC) determined by EDANA test method No. WSP 241.3 of the resulting water-absorbing polymer is between 27.1 g/g and 30.5 g/g and wherein the Absorption against a pressure of 0.7 psi (AAP) determined in accordance with EDANA Method No. WSP242.3 of the resulting water-absorbing polymer is between 23.0 and 25.1 g/g, wherein the anti-stick processing aid is a cationic surfactant, and that less than 10% of the water-absorbing polymer resulting in process step (iii) stick to the apparatus used subsequent to step (ii); and

wherein less than 10% of the water-absorbing polymer resulting from process step (iii) stick to the dryer plate section, 5 seconds after a 180° turn according to the determination of water-absorbing polymer gel stickiness as defined herein.

2. A process for producing a water-absorbing polymer in an apparatus, comprising the steps of (i) mixing

(α1) from 0.1 to 99.999% by weight of polymerizable, ethylenically unsaturated monomers containing acid groups, or salts thereof,

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

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

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

(α5) from 0 to 80% by weight of water, and

(α6) from 0 to 20% by weight of one or more assistants, where the sum of the weights of (α1) to (α5) is 100% by weight,

(ii) free-radical polymerization with crosslinking to form a water-absorbing polymer,

(iii) drying the water-absorbing polymer,

(iv) grinding and sieving the water-absorbing polymer to size,

(v) surface post-crosslinking the ground and sieved water-absorbing polymer and

(vi) drying and finishing the water-absorbing polymer, wherein an anti-stick processing aid is added before and/or in steps (iii) such that the anti-stick processing aid is added before step (iii) to the apparatus used subsequent to step (ii) and the degree of neutralization of component (α1) is at most 70 mol %; and wherein the anti-stick processing aid is applied by spraying, jetting, painting, brushing or coating onto drying plates, belts, trays or other receptacles coming into contact with a hydrogel polymer; wherein said drying plates, belts, trays or other receptacles are made of metal and have a metallic surface; wherein the anti-stick processing aid is a non-permanent anti-stick processing aid;

wherein the surface tension of the resulting water-absorbing polymer is between 69.9 and 80 mN/m and wherein the Centrifuge Retention Capacity (CRC) determined by EDANA test method No. WSP 241.3 of the resulting water-absorbing polymer is between 27.1 g/g and 30.5 g/g and wherein the Absorption against a pressure of 0.7 psi (AAP) determined in accordance with EDANA Method No. WSP242.3 of the resulting water-absorbing polymer is between 23.0 and 25.1 g/g, wherein the anti-stick processing aid is a cationic surfactant, and that less than 10% of the water-absorbing polymer resulting in process step (iii) stick to the apparatus used subsequent to step (ii); and

wherein less than 10% of the water-absorbing polymer resulting from process step (iii) stick to the dryer plate section, 5 seconds after a 180° turn according to the determination of water-absorbing polymer gel stickiness as defined herein.

3. The process according to claim 1 , characterized in that the degree of neutralization of component (α1) is at most 75 mol %.

4. The process according to claim 1 , wherein the cationic surfactant is fatty acid esterquats.

5. The process according to claim 2 , wherein the cationic surfactant is fatty acid esterquats.