While maintaining a high absorption performance and fluidity in a dry state is high, can prevent the adhesion caking and blocking, to a device such as moisture absorption, and further, the present invention, a surface when in contact with the absorbing solution without impairing the absorption properties of the tension decrease and less likely, it is intended to obtain a particulate water-absorbing agent flow and increased bulk density. It is to be understood that the surface-crosslinking treatment of water-absorbent resin having a crosslinked structure, (i) mass average particle diameter (D50) in 200~600μm, the particulate water absorbing agent of the present invention are those having a particle diameter of 850μm is less than 150μm more But 95 to 100 weight percent of the total, 0.25 to 0.45, 0-18% is (iii) the degree of compression, saline (iv) of 20 ℃ logarithmic standard deviation (ii) the particle size distribution (σζ) I is characterized in that the surface tension of the supernatant after 4 minutes is 55mN / m or more, from dispersing the particulate water absorbing agent 0.5g in 50ml.本発明は、高い吸収性能を維持したまま、乾燥状態での流動性が高く、かつ、吸湿時のブロッキングやケーキング、装置等への付着を防止でき、さらには、吸収液と接触した場合に表面張力の低下が起こりにくく、かつ吸水特性を損なうことなく、流動性およびかさ密度を増大させた粒子状吸水剤を得ることを目的とする。本発明の粒子状吸水剤は、架橋構造を有する吸水性樹脂を表面架橋処理したものであって、(i)質量平均粒子径(D50)が200~600μmで、粒子径850μm未満150μm以上のものが全体の95~100重量%、(ii)粒度分布の対数標準偏差(σζ)が0.25~0.45、(iii)圧縮度が0~18%、(iv)20℃の生理食塩水50mlに該粒子状吸水剤0.5gを分散させてから4分後の上澄み液の表面張力が55mN/m以上、であることを特徴とする。
