Particle-shaped water absorbing agent and method for producing the same

摘要

An object of the present invention is to provide a particle-shaped water absorbing agent having a remarkably improved surface color and excellent water-absorbing properties (better water absorption capacity, and lower water soluble content and residual monomer content) at the same time. In order to attain the object, a particle-shaped water absorbing agent according to the present invention is a particle-shaped water absorbing agent whose main component is a polyacrylic acid and/or a salt thereof, the particle-shaped water absorbing agent having a surface color of Hunter b value in a range of −5 to 10, and having a cross-linking absorption property index (CPI) in a range of 1 to 100, the CPI defined by the following two equations:
GEX=(GVs+17)/Ln (water soluble content);  Equation 1:CPI=(GEX/residual monomer content)×100  Equation 3:where GVs is gel volume in saline, Ln (water soluble content) is a logarithm natural of water soluble content.

主权项

1. A particle-shaped water absorbing agent containing a resin of an acrylic acid and/or a salt thereof in a range of 70 to 99.9% by weight to the particle-shaped water absorbing agent, the particle-shaped water absorbing agent having a surface color of a Hunter b value in a range of −5 to 10 and a Hunter L value in a range of 90 to 100, and having a cross-linking absorption property index (CPI) in a range of 1 to 100, the CPI defined by the following equations:
GEX=(GVs+17)/Ln ( amount of extracted water-soluble polymer);   Equation 1: CPI=(GEX/residual monomer content)×100if the residual monomer content is not less than 20 ppm by weight; and   Equation 3: CPI=GEX−residual monomer amount if residual monomer content is less than 20 ppm by weight,   Equation 4: where GVs is gel volume in saline, Ln (amount of extracted water-soluble polymer) is a logarithm natural of amount of extracted water-soluble polymer; and wherein the particle-shaped water absorbing agent further contains one or more of components (i) to (iii): (i) an N-oxyl compound in a range of 0.01 to 10 ppm by weight; and a methoxyphenol compound in a range of 0 to 20 ppm by weight; (ii) a methoxyphenol compound in a range of 0.01 to 20 ppm by weight; and a manganese compound in a range of 0.01 to 10 ppm by weight (as MnO2); (iii) a polyalkyleneglycol of weight average molecular weight of 300 to 50000; and iron in a range of iron content in a range of 0.001 to 5 ppm by weight.