Water-absorbing agent, manufacture method thereof, and absorbent and absorbent article made therefrom

Abstract

We have found that to improve the heat retention by diapers and other absorbents, a heat retention indicator 1 of a water-absorbing resin which is defined in the present invention needs be 3.0° C./min or less and also that particular requirements need be met to satisfy this condition. If the requirements are met, a water-absorbing resin, absorbent, and absorbent article can be provided which has a heat retention indicator 1 of 0 to 3.0° C./min or less and which exhibits excellent heat retention and absorption.

1 . A water-absorbing agent, comprising a water-absorbing resin having a crosslinking structure constructed by polymerization of an unsaturated monomer component, wherein 
 the water-absorbing agent is surface-treated, and    the water-absorbing agent meets all of properties (1) through (4):    (1) heat retention indicator  1  (maximum temperature decrease per minute 5 to 10 minutes after 10 times swelling in a 0.90 wt. % sodium chloride at 50° C.) is from 0 to 3.0° C./min;    (2) a centrifuge retention capacity in a 0.90 wt. % aqueous solution of sodium chloride (30 minute value) is 34 g/g or less;    (3) an absorbency in a 0.90 wt. % aqueous solution of sodium chloride against a pressure of 2.0 kPa (60 minute value) is less than 30 g/g; and    (4) a saline flow conductivity (SFC) for a 0.69 wt. % aqueous solution of sodium chloride is less than 20×10 −7 cm 3 sec/g.    
   
   
       2 . The water-absorbing agent as set forth in  claim 1 , wherein 
 the water-absorbing agent is particles, and    the water-absorbing agent meets following conditions:    particles having diameters from 600 to 300 μm as specified by sieve classification account for 60 wt. % or more, and those less than 150 μm account for 3 wt. % or less; and    a standard deviation of logarithm (σζ) of particle size distribution is from 0.250 to 0.400.    
   
   
       3 . The water-absorbing agent as set forth in  claim 1 , further comprising water-insoluble inorganic fine particles, besides the water-absorbing resin.  
   
   
       4 . The water-absorbing agent as set forth in  claim 1 , wherein a heat retention indicator  2  (gel surface temperature 10 minutes after 10 times swelling in a 0.90 wt. % sodium chloride at 50° C.) is 20 20  C. or higher.  
   
   
       5 . The water-absorbing agent as set forth in  claim 1 , wherein a heat retention indicator  3  (time taken by a gel surface temperature to return to 37° C. after 10 times swelling in a 0.90 wt. % sodium chloride at 50° C.) is 120 seconds or longer.  
   
   
       6 . The water-absorbing agent as set forth in  claim 1 , wherein a mass-average particle diameter (specified by sieve classification) is from 400 to 600 μm.  
   
   
       7 . The water-absorbing agent as set forth in  claim 1 , further comprising polyol, besides the water-absorbing resin.  
   
   
       8 . An absorbent, comprising the water-absorbing agent as set forth in  claim 1  and hydrophilic fibers.  
   
   
       9 . An absorbent article, comprising the absorbent as set forth in  claim 8;  a liquid-permeable top sheet; and a liquid-impermeable back sheet.  
   
   
       10 . A method of manufacturing a water-absorbing agent containing a water-absorbing resin having a crosslinking structure constructed by polymerization of an unsaturated monomer component, comprising: 
 the polymerization step of polymerizing a monomer component containing an acid-group-containing unsaturated monomer as a major component to prepare a water-absorbing resin; and    the surface crosslinking treatment step of surface-crosslinking the water-absorbing resin obtained in the polymerization step,    wherein    in the polymerization step,    the water-absorbing resin is particles,    the water-absorbing resin has a centrifuge retention capacity of 35 g/g or more in 0.90 wt. % sodium chloride (30 minute value), and    the monomer component is polymerized so that the water-absorbing resin meets following conditions (1) and (2) on specific particle sizes:    (1) particles having diameters from 600 to 300 μm as specified by sieve classification account for 60 wt. % or more, and those less than 150 μm account for 3 wt. % or less; and    (2) a standard deviation of logarithm(σζ) of particle size distribution is from 0.250 to 0.400.    in the surface crosslinking step, the water-absorbing resin meeting conditions (1) and (2) on specific particle sizes is surface crosslinked in a surface crosslinking treatment process.    
   
   
       11 . The method as set forth in  claim 10 , wherein 
 in the surface crosslinking step,    the water-absorbing resin meeting conditions (1) and (2) on specific particle sizes in the polymerization step is surface-crosslinked until:    a centrifuge retention capacity in a 0.90 wt. % aqueous solution of sodium chloride (30 minute value) reaches 34 g/g or less; and    an absorbency in a 0.90 wt. % aqueous solution of sodium chloride against a pressure of 2.0 kPa (60 minute value) becomes less than 30 g/g.    
   
   
       12 . The method as set forth in  claim 10 , wherein the water-absorbing resin has a mass-average particle diameter of 400 μm to 600 μm.  
   
   
       13 . The water-absorbing agent as set forth in  claim 1 , wherein the unsaturated monomer is an acrylic acid (salt), and a ratio of a monomer other than the acrylic acid (salt) to the acrylic acid (salt) is 0 to 30 mole % inclusive.  
   
   
       14 . The absorbent as set forth in  claim 8 , wherein the water-absorbing agent accounts for 20 wt. % or more of a total of the water-absorbing agent and hydrophilic fibers.