Particulate water-absorbing agent and method for producing the same
[Problem] In an embodiment involving addition of a chelating agent in an upstream process of the process for production, such as the polymerization step, the residual ratio of the chelating agent in the final product, a particulate water-absorbing agent, is improved. [Solution] A particulate water-absorbing agent having a poly(meth)acrylic acid (salt)-based water-absorbing resin as a main component, containing a chelating agent having a nitrogen atom and an inorganic reducing agent having a sulfur atom, wherein the particulate water-absorbing agent has a chelating agent ratio of 0.8 to 1.8, as calculated by the following procedures (a) to (c): (a) subjecting the particulate water-absorbing agent to a predetermined impact test; (b) sieving the particulate water-absorbing agent subjected to the impact test into a particle group 1 with a particle size of less than 300 μm and a particle group 2 with a particle size of 300 μm or more and less than 850 μm using a JIS standard sieve; and (c) quantifying a content C1 of the chelating agent present in the particle group 1 and a content C2 of the chelating agent present in the particle group 2, and then dividing the C1 by the C2.
1 . A particulate water-absorbing agent having a poly(meth)acrylic acid (salt)-based water-absorbing resin as a main component, comprising a chelating agent having a nitrogen atom and an inorganic reducing agent having a sulfur atom,
wherein the particulate water-absorbing agent has a chelating agent ratio of 0.8 to 1.2, as calculated by the following procedures (a) to (c):
(a) subjecting the particulate water-absorbing agent to a predetermined impact test;
(b) sieving the particulate water-absorbing agent subjected to the impact test into a particle group 1 with a particle size of less than 300 μm and a particle group 2 with a particle size of 300 μm or more and less than 850 μm using a JIS standard sieve; and
(c) quantifying the content C1 of the chelating agent present in the particle group 1 and the content C2 of the chelating agent present in the particle group 2, and then dividing the C1 by the C2.
2 . The particulate water-absorbing agent according to claim 1 , wherein the color tone YI is 12 or less in an initial color tone test.
3 . The particulate water-absorbing agent according to claim 1 , wherein the content C7 of the chelating agent in the particulate water-absorbing agent is 10 to 5,000 ppm.
4 . The particulate water-absorbing agent according to claim 1 , wherein the chelating agent is at least one compound selected from the group consisting of amino-polyvalent carboxylic acids and amino-polyvalent phosphoric acids.
5 . The particulate water-absorbing agent according to claim 1 , wherein the inorganic reducing agent is a sulfite or a hydrogen sulfite.
6 . The particulate water-absorbing agent according to claim 1 , wherein the content of a residual monomer is 700 ppm or less.
7 . The particulate water-absorbing agent according to claim 1 , wherein the content of the inorganic reducing agent is 1 to 3,000 ppm.
8 . The particulate water-absorbing agent according to claim 1 , wherein a proportion of particles with a particle size of less than 850 μm is 90 to 100% by mass of the total.
9 . The water-absorbing agent according to claim 1 , having water insoluble inorganic fine particles with a volume-average particle size of 0.2 to 3 μm added to a particle surface of the particulate water-absorbing agent.
10 . A water absorbent article, comprising the particulate water-absorbing agent according to claim 1 .