Polyacrylic acid (salt)-based water absorbent resin, and method for producing polyacrylic acid (salt)-based water absorbent resin

Abstract

As a method for producing a polyacrylic acid (salt)-based water absorbent resin particle which less generates fine powder and has an excellent impact resistance and a high moisture content even in a case where the polyacrylic acid (salt)-based water absorbent resin particle is produced on a large scale, employed is a production method including the steps of: (a) adding a surface crosslinking agent solution to water absorbent resin powder to obtain a mixture; (b) reacting the mixture; and, thereafter (c) adding an aqueous liquid to at least one selected from the group consisting of (i) the water absorbent resin powder during the step (b) and (ii) the water absorbent resin powder after the step (b), an atmospheric dew point being not lower than 20° C. in the step (c), and a temperature of the water absorbent resin powder being higher than the atmospheric dew point in the step (c).

1 . A method for producing a polyacrylic acid (salt)-based water absorbent resin particle, comprising the steps of:
 (a) adding a surface crosslinking agent solution to water absorbent resin powder to obtain a mixture;   (b) reacting the mixture; and, thereafter   (c) adding an aqueous liquid to at least one selected from the group consisting of (i) the water absorbent resin powder during the step (b) and (ii) the water absorbent resin powder after the step (b),   an atmospheric dew point being not lower than 20° C. in the step (c), and   a temperature of the water absorbent resin powder being higher than the atmospheric dew point in the step (c).   
     
     
         2 . The method as set forth in  claim 1 , wherein the step (c) is carried out during the step (b). 
     
     
         3 . The method as set forth in  claim 1 , wherein the step (c) is carried out with respect to the water absorbent resin powder which exists in a heat reactor or in an active energy ray reactor. 
     
     
         4 . The method as set forth in  claim 1 , wherein the step (c) is carried out after the step (b). 
     
     
         5 . The method as set forth in  claim 1 , wherein the step (c) starts within 3 minutes after the step (b). 
     
     
         6 . The method as set forth in  claim 1 , wherein the step (c) is carried out with respect to the water absorbent resin powder during a cooling step after the step (b). 
     
     
         7 . The method as set forth in  claim 1 , wherein the temperature of the water absorbent resin powder is in a range from 50° C. to 150° C. in the step (c). 
     
     
         8 . The method as set forth in  claim 1 , wherein the water absorbent resin powder has a moisture content in a range from 2 wt % to 15 wt % in the step (c). 
     
     
         9 . The method as set forth in  claim 1 , wherein quantity of the aqueous liquid to be added relative to the water absorbent resin powder is in a range from 0.1 wt % to 14 wt %. 
     
     
         10 . The method as set forth in  claim 1 , wherein the polyacrylic acid (salt)-based water absorbent resin particle has a moisture content in a range from 5 wt % to 20 wt %. 
     
     
         11 . The method as set forth in  claim 1 , wherein the aqueous liquid contains at least one kind selected from the group consisting of a deodorant, an antimicrobial agent, an anti-coloring agent, a chelating agent, an inorganic salt, an acidic compound, a reducing agent, an alkaline compound, and a surfactant. 
     
     
         12 . The method as set forth in  claim 1 , wherein a mass average particle diameter (D50) increase ratio (%) at which granulation increases a D50 is in a range from 5% to 50%. 
     
     
         13 . A polyacrylic acid (salt)-based water absorbent resin particle having (i) a moisture content in a range from 5 wt % to 20 wt %, (ii) a water absorption capacity without load CRC (ERT 441. 2-02) in a range from 30 to 45 (g/g), (iii) a water absorption capacity under load AAP (ERT 442.2-02) in a range from 30 to 40 (g/g), and (iv) a total of the CRC and the AAP of not less than 65 (g/g). 
     
     
         14 . The polyacrylic acid (salt)-based water absorbent resin particle as set forth in  claim 13 , containing at least one kind selected from the group consisting of a deodorant, an antimicrobial agent, an anti-coloring agent, a chelating agent, an inorganic salt, an acidic compound, a reducing agent, an alkaline compound, and a surfactant. 
     
     
         15 . The polyacrylic acid (salt)-based water absorbent resin particle as set forth in  claim 13 , being granulated. 
     
     
         16 . The polyacrylic acid (salt)-based water absorbent resin particle as set forth in  claim 13 , wherein a mass average particle diameter (D50) decrease ratio (%) at which impact decreases a D50 is in a range from 0% to 30%. 
     
     
         17 . Absorbent articles, comprising a polyacrylic acid (salt)-based water absorbent resin particle as set forth in  claim 13 .