The present invention relates a method for producing a water absorption resin and a water absorption resin with specific properties provided by the method for producing water absorption resin. The method for producing water absorption resin is capable of producing a water absorption resin excellent in water absorption, that is, high water-reservation property, having high water-absorption property and high vertical diffusion water-absorption property under a loading, and the content of residue monomers is small, suitable for using as an absorption article. The method for producing a water absorption resin provided in this invention is characterized by: when using both an azo compound and a peroxide in a hydrocarbon dispersing solvent in the presence of a dispersing stabilizer, and bringing a water-soluble ethylene unsaturated monomer into inverse phase suspension polymerization in the presence of an inner-crosslinker, with respect to the water-soluble ethylene unsaturated monomer for polymerization per 100 mole, the using amount of the azo compound, the peroxide and the inner-crosslinker being set to A mole B mole C mole, respectively, and satisfying the following functions, 0.10 ≦ B/(A+B) (1)0.055 ≦ B+9×C ≦ 0.120 (2) and adding a post-crosslinker for a post-crosslinking reaction after the polymerization.本發明為關於一種吸水性樹脂之製造方法,該吸水性樹脂的製造方法可製造吸水性能優異,亦即保水能力高,具有在負載下之高吸水能力及高垂直擴散吸水能力,而且餘留之單體含量少,適於使用為吸收性物品的吸水性樹脂,以及以該吸水性樹脂之製造方法所提供的具有特定性能之吸水性樹脂。本發明所提供之吸水性樹脂的製造方法,其特徵為:在分散安定劑存在下,在烴分散溶劑中,併用偶氮系化合物與過氧化物,且在內交聯劑存在下使水溶性乙烯性不飽和單體逆相懸浮聚合時,在偶氮系化合物、過氧化物及內交聯劑的使用量,相對於聚合所使用之水溶性乙烯性不飽和單體每100莫耳,分別當作A莫耳、B莫耳、C莫耳時,可滿足以下關係式0.10≦B/(A+B) (1)0.055≦B+9×C≦0.120 (2),而且在經過聚合後之後再添加後交聯劑進行後交聯反應。1‧‧‧滴定管部2‧‧‧導管3‧‧‧測定檯4‧‧‧測定部5‧‧‧吸水性樹脂10‧‧‧滴定管11‧‧‧空氣導管12‧‧‧開關閥13‧‧‧開關閥14‧‧‧橡膠塞40‧‧‧圓筒41‧‧‧尼龍濾網42‧‧‧負載100‧‧‧測定裝置
