Particulate water absorbing agent and water absorbent article
A water absorbent resin (water absorbing agent) and method for producing it are provided which improve, in a water absorbent article (in particular, a diaper) including a water absorbent resin as a water absorbing agent, the absolute absorption amount (g), liquid absorbing times (in particular, liquid absorbing times at the second instance and later), re-wet (g), and diffusion distance (%) of the water absorbent article. A particulate water absorbing agent of the present invention has a CRC, a proportion of particles with sizes of 600 μm to 150 μm as defined through a standard-sieve classification, an SST, and the value of the difference between an FST and the SST each within a predetermined range.
1. A particulate water absorbing agent, comprising:
a polyacrylic acid (salt)-based water absorbent resin as a main component,
the polyacrylic acid (salt)-based water absorbent resin being a surface-crosslinked water absorbent resin and internally crosslinked using an internal crosslinking agent in an amount of 0.04 mol % or more to 0.07 mol % or less relative to a monomer,
the particulate water absorbing agent having a swelling rate (CRC) of 32 g/g to 50 g/g relative to 0.9-mass % saline,
the particulate water absorbing agent including, at a proportion of 80 mass % or more, a particle having a size of 600 μm to 150 μm as defined through a standard-sieve classification,
the particulate water absorbing agent having a second-instance pure-water 50-fold swelling time (SST (in seconds)) of 70 seconds or less,
a difference (DST=SST−FST) between a first-instance pure-water 50-fold swelling time (FST (in seconds)) and the second-instance pure-water 50-fold swelling time (SST (in seconds)) being +10 seconds or less,
the particulate water absorbing agent including, at 3 mass % or less, a particle that passes through a 150 μm mesh as defined through a standard-sieve classification.
2. The particulate water absorbing agent according to claim 1 , further comprising:
a water-insoluble inorganic fine particle as a liquid permeability improving agent,
the water-insoluble inorganic fine particle having a volume average particle size of 1 nm or higher and 50 μm or less.
3. The particulate water absorbing agent according to claim 2 ,
wherein:
the water-insoluble inorganic fine particle is contained in an amount of 0.05 part by mass to 5.0 parts by mass relative to 100 parts by mass of the particulate water absorbing agent.
4. The particulate water absorbing agent according to claim 2 ,
wherein:
the water-insoluble inorganic fine particle is made of silicon dioxide.
5. The particulate water absorbing agent according to claim 1 ,
wherein:
the particulate water absorbing agent has a swelling rate under load (AAP 1.9 kPa) which swelling rate is 24 gig or higher relative to 0.9-mass % saline.
6. The particulate water absorbing agent according to claim 1 , further comprising:
as a liquid permeability improving agent, a water-soluble polyhydric metal cation in an amount of 0.01 part by mass to 5.0 parts by mass relative to 100 parts by mass of the particulate water absorbing agent.
7. The particulate water absorbing agent according to claim 6 ,
wherein:
the water-soluble polyhydric metal cation is an aluminum cation.
8. The particulate water absorbing agent according to claim 1 ,
wherein:
the DST is 0 seconds or less.
9. The particulate water absorbing agent according to claim 1 ,
wherein:
the particulate water absorbing agent includes, at 5 mass % or less, a particle that does not pass through a 710-μm mesh as defined through a standard-sieve classification.
10. A water absorbent article, comprising:
the particulate water absorbing agent according to claim 1 .