Superabsorbent polymer with high permeability

Abstract

The invention relates to absorptive, crosslinked polymers which are based on partly neutralized, monoethylenically unsaturated monomers carrying acid groups wherein the absorptive crosslinked polymer may be coated with a thermoplastic polymer, and have improved properties, in particular in respect of their capacity for transportation of liquids in the swollen state, and which has a high gel bed permeability and high centrifuge retention capacity.

1 . A particulate superabsorbent polymer comprising a superabsorbent polymer consisting essentially of:
 a) from about 55 to about 99.9 wt. % of polymerizable unsaturated acid group containing monomers;   b) from about 0.001 to about 5.0% by weight of internal crosslinking agent based on the weight of a);   wherein elements a) and b) are polymerized and prepared into particulate superabsorbent polymer; wherein the particulate superabsorbent polymer further comprise the following surface additives   c) from about 0.001 to about 5.0% by weight of surface crosslinking agent applied to the particle surface based on dry polymer powder weight;   d) from about 0.01% to about 5 wt. % by weight of a penetration modifier immediately before, during or immediately after the surface crosslinking step based on dry polymer powder weight;   e) from about 0.01 to about 5% by weight of an insoluble, inorganic powder based on dry polymer powder weight; and   f) from about 0.01 to 0.5% by weight of a thermoplastic polymer based on dry polymer powder weight, said thermoplastic polymer having a thermoplastic melt temperature wherein the thermoplastic polymer is applied on the particle surface coincident with or followed by a temperature at least about the thermoplastic melt temperature or greater,   wherein the particulate superabsorbent polymer has a degree of neutralization of more than about 25%; and wherein the particulate superabsorbent polymer has a gel bed permeability I of at least about [54000e −0.18x +100]×10 −9  cm 2  wherein x is the numeric value of the centrifuge retention capacity.   
     
     
         2 . The particulate superabsorbent polymer of  claim 1  wherein the thermoplastic polymer is selected from polyethylene, polyesters, polyurethanes, linear low density polyethylene (LLDPE), ethylene acrylic acid copolymer (EAA), styrene copolymers, ethylene alkyl methacrylate copolymer (EMA), polypropylene (PP), ethylene vinyl acetate copolymer (EVA) or blends thereof, or copolymers thereof. 
     
     
         3 . The particulate superabsorbent polymer of  claim 1  having a Dust Values of about 4 or less. 
     
     
         4 . The particulate superabsorbent polymer of  claim 1  having a shear modulus of less than about 9500 dynes/cm 2 . 
     
     
         5 . The particulate superabsorbent polymer according to  claim 1  comprising from about 0.1 to about 5% by weight of a multivalent metal salt based on the dry polymer powder weight. 
     
     
         6 . The particulate superabsorbent polymer according to  claim 1  wherein the insoluble, inorganic powder is silica. 
     
     
         7 . A particulate superabsorbent polymer comprising a superabsorbent polymer consisting essentially of:
 a) from about 55 to about 99.9 wt. % of polymerizable unsaturated acid group containing monomers;   b) from about 0.001 to about 5.0 wt. % based on the weight of a) of internal crosslinking agent;   wherein elements a) and b) are polymerized and prepared into particulate superabsorbent polymer; wherein the particulate superabsorbent polymer further comprise the following surface additives   c) from about 0.001 to about 5.0% by weight of surface crosslinking agent applied to the particle surface based on dry polymer powder weight;   d) from about 0.01% to about 5% by weight of a penetration modifier immediately before, during or immediately after the surface crosslinking step based on dry polymer powder weight;   e) from 0 to about 5% by weight of a multivalent metal salt on the particle surface based on dry polymer powder weight;   f) from 0 to 2% by weight of a surfactant on the particle surface based on dry polymer powder weight;   g) from about 0.01 to about 5% by weight of an insoluble, inorganic powder based on dry polymer powder weight; and   h) from about 0.01 to 0.5% by weight of a thermoplastic polymer based on dry polymer powder weight, the thermoplastic polymer having a thermoplastic melt temperature wherein the thermoplastic polymer is applied on the particle surface coincident with or followed by a temperature at least about the thermoplastic melt temperature or greater,   wherein the composition has a degree of neutralization of more than about 25%; having the characteristics of centrifuge retention capacity of about 25 g/g or more; having a Dust Values of about 4 or less.   
     
     
         8 . The particulate superabsorbent polymer according to  claim 7  wherein gel bed permeability I is at least about [54000e −0.18x +100]×10 −9  cm 2  wherein x is the numeric value of the centrifuge retention capacity. 
     
     
         9 . The particulate superabsorbent polymer according to  claim 7  wherein the thermoplastic polymer is selected from polyethylene, polyesters, polyurethanes, linear low density polyethylene (LLDPE), ethylene acrylic acid copolymer (EAA), styrene copolymers, ethylene alkyl methacrylate copolymer (EMA), polypropylene (PP), ethylene vinyl acetate copolymer (EVA) or blends thereof, or copolymers thereof. 
     
     
         10 . The particulate superabsorbent polymer according to  claim 7  having a gel bed permeability I of about 500×10 −9  cm 2  or more. 
     
     
         11 . A method to make a particulate superabsorbent polymer comprising the steps of:
 a) preparing a superabsorbent polymer by the process of polymerizing from about 55 to about 99.9% weight of polymerizable unsaturated acid group containing monomers, and from about 0.001 to about 5% weight of internal crosslinking agent based on the polymerizable unsaturated acid group containing monomers, and a neutralization such that the superabsorbent polymer has a degree of neutralization of more than about 25%;   b) preparing particulate superabsorbent polymer from the superabsorbent polymer;   c) treating the particulate superabsorbent polymer with surface additives including:
 i) from about 0.001 to about 5.0% weight of a surface crosslinking agent based on dry polymer powder weight; 
 ii) from about 0.01 to about 10% weight of a penetration modifier based on dry polymer powder weight; 
 iii) from about 0.01 to about 5% weight of a multivalent metal salt based on dry polymer powder weight; 
 iv) from 0 to 2% weight of a surfactant based on dry polymer powder weight; 
 v) from about 0.01 to about 5% weight of an insoluble, inorganic powder based on dry polymer powder weight; and 
 vi) from about 0.01 to 0.5% weight of a thermoplastic polymer based on dry polymer powder weight is applied on the particle surface, heat treating the coated superabsorbent polymer particle; 
   wherein the superabsorbent polymer composition has the characteristics of centrifuge retention capacity of about 25 g/g or more; and a Dust Values of about 4 or less.   
     
     
         12 . The method of  claim 11  wherein in step a) at least about 50% weight of the acid groups include carboxyl groups, the acid groups are neutralized to at least 59 mole %, and the internal crosslinking agent is from about 1.0 to about 3.0% weight based on the total amount of the polymerizable unsaturated acid group containing monomers. 
     
     
         13 . The method of  claim 11  wherein the heat treatment of the coated superabsorbent polymer is from about 100° C. to about 300° C. 
     
     
         14 . The method of  claim 11  wherein the heat treatment of the coated superabsorbent polymer is from about 150° C. to about 250° C. 
     
     
         15 . The method of  claim 11  wherein the superabsorbent polymer composition has a gel bed permeability I of at least about [54000e −0.18x +100]×10 −9  cm 2  wherein x is the numeric value of the centrifuge retention capacity. 
     
     
         16 . The method of  claim 11  wherein the particulate superabsorbent polymer has a gel bed permeability I of about 500×10 −9  cm 2  or more. 
     
     
         17 . The method of  claim 11  wherein the insoluble, inorganic powder is silica.