Absorbing agent, process of manufacturing same, and absorbent product containing same

Abstract

An absorbing agent has a diffusing absorbency under pressure of not less than 25 g/g when 60 minutes elapsed after absorption is started, and a water-soluble content is above 0 percent by weight and not more than 7 percent by weight. The absorbing agent is prepared by surface-crosslinking a precursor of the absorbing agent obtained by performing an aqueous solution polymerization of a hydrophilic unsaturated monomer having not less than 50 mole percent neutralized acrylic acid as a main component using a specific crosslinking agent having a main component composed of an ester compound of a specific polyhydroxy alcohol and an unsaturated carboxylic acid, and a high-boiling component having at least two alcohol structures in a molecule as a specific ratio. As a result, an absorbing agent having excellent properties such as the diffusing absorbency under pressure is high, the water soluble content is small, and the amount of wet back of the aqueous liquid after a long period of time is small, water absorbency under pressure can be stably maintained for a long period of time can be achieved.

What is claimed is:  
     
       1. An absorbing agent formed from a precursor prepared by performing an aqueous solution polymerization of a hydrophilic unsaturated monomer having at least 50 mole percent neutralized an acrylic acid and/or an acrylic acid salt as a main component, and having a crosslinked density in the vicinity of a surface of said agent higher than a crosslinked density at an inside portion thereof, said absorbing agent having a diffusing absorbency under pressure of not less than 25 30 g/g when 60 minutes have elapsed after absorption has started. 
     
     
       2. An The absorbing agent formed from a precursor prepared by performing an aqueous solution polymerization of a hydrophilic unsaturated monomer having at least 50 mole percent neutralized acrylic acid as a main component, and having a crosslinked density in the vicinity of a surface of said agent higher than a crosslinked density at an inside portion thereof, said absorbing agent having as set forth in  claim 1 , wherein  
       a diffusing absorbency under pressure of is not less than 15 32 g/g when 30 60 minutes have elapsed after absorption has started.  
     
     
       3. The absorbing agent as set forth in claim  2   1 , wherein: 
       a diffusing absorbency under pressure is not less than 25 34 g/g when 60 minutes have elapsed after absorption has started.  
     
     
       4. An The absorbing agent formed from a precursor prepared by performing an aqueous solution polymerization of a hydrophilic unsaturated monomer having at least 50 mole percent neutralized acrylic acid as a main component, and having a crosslinked density in the vicinity of a surface of said agent higher than a crosslinked density at an inside portion thereof, said absorbing agent having as set forth in  claim 1 , wherein  
       a diffusing absorbency under pressure of is not less than 15 g/g when 20 30 minutes have elapsed after absorption has started.  
     
     
       5. The absorbing agent as set forth in claim  4   1 , wherein: 
       a diffusing absorbency under pressure is not less than 25 15 g/g when 60 20 minutes have elapsed after absorption has started.  
     
     
       6. The absorbing agent as set forth in  claim 4 , wherein: 
       a diffusing absorbency under pressure is not less than 30 g/g when 60 minutes elapsed after absorption has started.  
     
     
       7. The absorbing agent as set forth in  claim 1 , wherein: 
       a water soluble component amount is above 0 and not more than 7 percent by weight.  
     
     
       8. The absorbing agent as set forth in  claim 1 , containing a dispersant. 
     
     
       9. The absorbing agent as set forth in  claim 8 , wherein: 
       said dispersant is contained in an amount in a range of 0.005 parts by weight to 0.5 parts by weight with respect to 100 parts by weight of a the precursor of the absorbing agent, composed of a monomer.  
     
     
       10. An absorbent material, comprising: 
       an absorbing agent in an amount of not less than 40 percent by weight of an absorbing agent formed from a precursor prepared by performing an aqueous solution polymerization of a hydrophilic unsaturated monomer having at least 50 mole percent neutralized acrylic acid as a main component, and having a cross-linked density in the vicinity of a surface of said agent higher than a crosslinked density at an inside portion thereof , said absorbing agent having a diffusing absorbency under pressure of  25 not less than 30  g/g when 60 minutes have elapsed after absorption has started.  
     
     
       11. The absorbent material as set forth in  claim 10 , wherein: 
       said absorbing agent has a diffusing absorbency under pressure isof not less than 1532 g/g when 3060 minutes have elapsed after absorption has started.  
     
     
       12. The absorbent material as set forth in  claim 10 , further comprising: 
       a hydrophilic fiber.  
     
     
       13. The absorbent material as set forth in  claim 12 , wherein: 
       said hydrophilic fiber is contained in an amount in a range of above 0 percent by weight and not more than 60 percent by weight.  
     
     
       14. The absorbent material as set forth in  claim 12 , wherein: 
       said absorbing agent is contained in an amount of not less than 50 percent by weight with respect to a total amount of said absorbing agent and said hydrophilic fiber.  
     
     
       15. The absorbent material as set forth in  claim 10 , further comprising: 
       an adhesive binder.  
     
     
       16. An absorbent product, comprising: 
       an absorbent material including an absorbing agent formed from a precursor prepared by performing an aqueous solution polymerization of a hydrophilic unsaturated monomer having at least 50 mole percent neutralized acrylic acid as a main component, and having a cross-linked density in the vicinity of a surface of said agent higher than a crosslinked density at an inside portion thereof, said absorbing agent having a diffusing absorbency under pressure of not less than 25 30 g/g when 60 minutes have elapsed after absorption has started, and a water soluble content in a range of greater than component amount of above  0 percent by weight and not more than  7 percent by weight.  
     
     
       17. The absorbent product as set forth in  claim 16 , wherein: 
       said absorbent material absorbing agent further contains a hydrophilic fiber in an amount in a range of above 0 percent by weight and not more than 60 percent by weight with respect to said absorbing agent.  
     
     
       18. The absorbent product as set forth in  claim 17 , wherein: 
       said absorbent material includes said hydrophilic fiber is contained in an amount in a range between 20 percent by weight and to 40 percent by weight with respect to said absorbing agent.  
     
     
       19. The absorbent product as set forth in  claim 16 , wherein: 
       said absorbent material further includes contains an adhesive binder.  
     
     
       20. An absorbent product comprising: 
       an absorbing layer of  claim 1  including an absorbent material being sandwiched between a sheet which is permeable to liquid and a sheet which is impermeable to liquid, said absorbing layer containing an absorbing agent having a diffusing absorbency under pressure of not less than  30  g/g when  60  minutes have elapsed after absorption has started.  
     
     
       21. A process of manufacturing an absorbing agent, comprising the steps of: 
       performing an aqueous solution polymerization of a hydrophilic unsaturated monomer having at least 50 mole percent neutralized acrylic acid as a main component in a presence of a dispersant to prepare a precursor of said absorbing agent, using a crosslinking agent composed of a main component and a high-boiling point component in a range of not less than 0.05 mole percent and not more than 0.5 mole percent with respect to a total amount of said hydrophilic unsaturated monomer,  
       wherein a ratio in weight of the main component of said crosslinking agent to said high-boiling point component is in a range of 75/25 to 99/1,  
       said main component of said crosslinking agent is composed of an ester compound including a polyhydroxy polyvalent alcohol having not more than six carbon atoms and at least three hydroxy groups and an unsaturated carboxylic acid, a ratio in molecular weight of the main component of said crosslinking agent to the a standard compound is in a range of not less than 0.7 and less than 1.3 based on a the molecular weight of a the standard compound wherein all hydroxy group of the polyvalent alcohol are ester-linked to the unsaturated carboxylic acid, and said high-boiling point component includes at least two alcohol structures in a molecule;  
       adjusting said precursor of said absorbing agent so as to have a water content of not more than 10 percent, an average particle diameter in a range of 200 μm-600 μm, and a ratio of particles having a diameter of not more than 106 μm of not more than 10 percent by weight; and  
       applying a heat treatment to said precursor of said absorbing agent in a presence of a surface crosslinking agent.  
     
     
       22. The process of manufacturing the absorbing agent as set forth in  claim 21 , wherein: 
       said surface crosslinking agent is composed of a first surface crosslinking agent reactive to a carboxyl group having a solubility parameter (SP value) of not less than 12.5 (cal/cm 3 ) 1/2  and a second surface crosslinking agent having a solubility parameter of less than 12.5 (cal/cm 3 ) 1/2 ; and  
       the heat treatment is performed at a temperature of not less than 160° C.  
     
     
       23. The absorbent material as set forth in  claim 10 , wherein: 
       
         said absorbing agent has a diffusing absorbency under pressure of not less than  34  g/g when  60  minutes have elapsed after absorption has started. 
       
     
     
       24. The absorbent material as set forth in  claim 10 , wherein: 
       
         said absorbing agent has a diffusing absorbency under pressure of not less than  15  g/g when  30  minutes have elapsed after absorption has started. 
       
     
     
       25. The absorbent material as set forth in  claim 10 , wherein: 
       
         said absorbing agent has a diffusing absorbency under pressure of not less than  15  g/g when  20  minutes have elapsed after absorption has started. 
       
     
     
       26. The absorbent material as set forth in  claim 16 , wherein: 
       
         said absorbing agent has a diffusing absorbency under pressure of not less than  32  g/g when  60  minutes have elapsed after absorption has started. 
       
     
     
       27. The absorbent material as set forth in  claim 16 , wherein: 
       
         said absorbing agent has a diffusing absorbency under pressure of not less than  34  g/g when  60  minutes have elapsed after absorption has started. 
       
     
     
       28. The absorbent material as set forth in  claim 16 , wherein: 
       
         said absorbing agent has a diffusing absorbency under pressure of not less than  15  g/g when  30  minutes have elapsed after absorption has started. 
       
     
     
       29. The absorbent material as set forth in  claim 16 , wherein: 
       
         said absorbing agent has a diffusing absorbency under pressure of not less than  15  g/g when  20  minutes have elapsed after absorption has started. 
       
     
     
       30. The absorbing agent as set forth in  claim 1 , 
         said agent is prepared by applying a heat treatment to a precursor having an internal crosslinking structure in the presence of a first surface crosslinking agent having a solubility parameter  ( SP value )  of not less than  12 . 5   ( cal/cm   3 ) 1/2    and a second surface crosslinking agent having a solubility parameter of less than  12 . 5   ( cal/cm   3 ) 1/2   .