Water-Absorbent Resin And Production Process Therefore
Patent #: 7,183,456
Inventor(s): Takumi Hatsuda, Yoshio Irie, Masatoshi Nakamura, Katsuyuki Wada, Shinichi Fujino, Kazuki Kimura and Kunihiko Ishizaki
Company: Nippon Shokubai Co., Ltd.
Patented is a water-absorbent resin, which is surface-crosslinked with a surface-crosslinking agent including at least a polyhydric alcohol. The water absorbent resin before surface-crosslinking is obtained by polymerizing hydrophilic monomers comprising a major proportion of either or both acrylic acid and its salt (neutralized product). The water absorbent resin has a particle size distribution such that the ratio of particles having particle diameters of smaller than 150 Ìm is not more than 5% by weight and exhibits an absorption capacity without a load of not less than 30 g/g. The water absorbent resin is characterized in that: a single-layer absorption capacity (10 min.) of particles with diameters of 600 to 300 Ìm is not less than 30 g/g under a load; the single-layer absorption capacity (60 min.) of particles with particle diameters of 600 to 300 Ìm is not less than 30 g/g under a load; the single-layer absorption capacity (10 min.) of particles with particle diameters of 300 to 150 Ìm is not less than 30 g/g under a load; and the single-layer absorption capacity (60 min.) of particles with particle diameters of 300 to 150 Ìm is not less than 30 g/g under a load. The single-layer absorption capacity is measured under the following conditions: (a) the liquid being absorbed is a synthetic urine (comprising 0.2% by weight of sodium sulfate, 0.2% by weight of potassium chloride, 0.05% by weight of magnesium chloride 6 hydrates, 0.025% by weight of calcium chloride dihydrate, 0.085% by weight of ammonium dihydrogen phosphate, 0.015% by weight of diammonium hydrogen phosphate and 99.425% by weight of deionized water) at 25±2° C; (b) the load applied to the measurement sample during the absorption is 50 g/cm2 (4.83 kPa); (c) the amount of the water absorbent resin as a measurement sample is 0.055±0.005 g; and (d) the water-absorbent resin as a measurement sample is uniformly spread on the wire net made of stainless steel attached to the bottom of the cylinder having an internal diameter of 60 mm, wherein the absorption capacity without a load is measured with a sample drained with a centrifuge after it is immersed into an aqueous sodium chloride solution of 0.9% by weight for 30 minutes.
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