JP4326752B2 - Method for producing water-absorbing agent - Google Patents

Description

ここで、
Ｆ_s（ｔ＝０）：ｇ／ｓで表した流速
Ｌ₀：ｃｍで表したゲル層の高さ
ρ：ＮａＣｌ溶液の密度（１．００３ｇ／ｃｍ³）
Ａ：セル４１中のゲル層上側の面積（２８．２７ｃｍ²）
ΔＰ：ゲル層にかかる静水圧（４９２０ｄｙｎｅ／ｃｍ²）
およびＳＦＣ値の単位は（１０^-7×ｃｍ³×ｓ×ｇ^-1）である。
【００９３】
図１に示す装置としては、タンク３１には、ガラス管３２が挿入されており、ガラス管３２の下端は、０．６９重量％生理食塩水３３をセル４１中の膨潤ゲル４４の底部から、５ｃｍ上の高さに維持できるように配置した。タンク３１中の０．６９重量％生理食塩水３３は、コック付きＬ字管３４を通じてセル４１へ供給された。セル４１の下には、通過した液を補集する容器４８が配置されており、補集容器４８は上皿天秤４９の上に設置されていた。セル４１の内径は６ｃｍであり、下部の底面にはＮｏ．４００ステンレス製金網（目開き３８μｍ）４２が設置されていた。ピストン４６の下部には液が通過するのに十分な穴４７があり、底部には吸水剤あるいはその膨潤ゲルが、穴４７へ入り込まないように透過性の良いガラスフィルター４５が取り付けてあった。セル４１は、セルを乗せるための台の上に置かれ、セルと接する台の面は、液の透過を妨げないステンレス製の金網４３の上に設置した。
【００９４】
人工尿（１）は、塩化カルシウムの２水和物０．２５ｇ、塩化カリウム２．０ｇ、塩化マグネシウムの６水和物０．５０ｇ、硫酸ナトリウム２．０ｇ、りん酸２水素アンモニウム０．８５ｇ、りん酸水素２アンモニウム０．１５ｇ、および、純水９９４．２５ｇを加えたものを用いた。
（５）機械的ダメージ試験
図２に示すガラス製容器（山村硝子社製マヨネーズ瓶、商品名：Ａ−２９）に吸水剤３０ｇとガラスビーズ（玉径約６ｍｍの精密分留充填用ソーダ石灰ガラスビーズ）１０ｇを入れた。これを図３に示す分散機（東洋精機製作所社製、Ｎｏ．４８８試験用分散機）に備えられたクランプ間に挟み固定し、１００Ｖ／６０Ｈｚで振動回転数７５０ｃｐｍの振動を１０分間与えた。これにより、上記分散機に固定された容器は、分散機における上記クランプの取り付け面に対して左右に各々１２．５°（合計２５°）傾斜運動すると同時に、前後に各々８ｍｍ（合計１６ｍｍ）振動することにより、容器内部の吸水剤に衝撃を与える。上記衝撃は、吸水剤の製造工程中に吸水剤が受ける衝撃力を代表するものとして経験的に定められた力であるが、製造後の輸送や吸水体製造時のダメージにも広く適用できるものである。本発明において、機械的ダメージを与える場合は、特に、吸水剤の製造時、吸水体の製造時を想定したものである。さらに、ＳＦＣ変化指数、ＳＦＣ変動係数、ＳＦＣ変動率は、吸水体内部における吸水剤の性能のばらつきを測る指標である。よって粒度別の物性を測定する場合は、実験室（１回の製造工程で得られる吸水剤の量が２０ｋｇ以下）のスケールにおいて製造された吸水剤は、すべて前記機械的ダメージを与えなければならない。
【００９５】
（６）可溶分（水可溶成分）量
２５０ｍｌ容量の蓋付きプラスチック容器に０．９重量％生理食塩水溶液（生理食塩水）の１８４．３ｇを測り取り、その水溶液中に吸水性樹脂１．００ｇを加え１６時間攪拌することにより樹脂中の可溶分を抽出した。この抽出液を濾紙１枚（ＡＤＶＡＮＴＥＣ東洋株式会社、品名：（ＪＩＳ Ｐ ３８０１、Ｎｏ．２）、厚さ０．２６ｍｍ、保留粒子径５μｍ）を用いて濾過することにより得られた濾液の５０．０ｇを測り取り測定溶液とした。
はじめに生理食塩水だけを、まず、０．１ＮのＮａＯＨ水溶液でｐＨ１０まで滴定を行い、その後、０．１ＮのＨＣｌ水溶液でｐＨ２．７まで滴定して空滴定量（［ｂＮａＯＨ］ｍｌ、［ｂＨＣｌ］ｍｌ）を得た。
【００９６】
同様の滴定操作を測定溶液についても行うことにより滴定量（［ＮａＯＨ］ｍｌ、［ＨＣｌ］ｍｌ）を求めた。
例えば既知量のアクリル酸とそのナトリウム塩からなる吸水性樹脂の場合、そのモノマーの平均分子量と上記操作により得られた滴定量をもとに、吸水性樹脂中の可溶分量を以下の計算式により算出することができる。未知量の場合は滴定により求めた中和率を用いてモノマーの平均分子量を算出する。
可溶分（重量％）＝０．１×（平均分子量）×１８４．３×１００×(［ＨＣｌ］−［ｂＨＣｌ］)／１０００／１．０／５０．０
中和率（ｍｏｌ％）＝（１−（［ＮａＯＨ］−［ｂＮａＯＨ］）／（［ＨＣｌ］−［ｂＨＣｌ］））×１００
（７）表層可溶分（水可溶成分）量
２５０ｍｌ容量の蓋付きプラスチック容器に０．５０重量％生理食塩水溶液の１００ｇを測り取り、その水溶液中に吸水剤０．５０ｇを加え、１時間吸水剤中の表層可溶分を抽出した。この抽出操作において、攪拌は初期の吸水剤の分散および最後の液の均一化のみを目的に攪拌し、前記以外は攪拌を行わない。具体的には、表層可溶分の抽出は静置で行い、抽出前後の１分間のみ攪拌（攪拌速度：４００ｒｐｍ、攪拌子：テフロン（登録商標）製（２．５ｃｍ））を行う。この抽出液を濾紙１枚（ＡＤＶＡＮＴＥＣ東洋株式会社、品名：（ＪＩＳ Ｐ ３８０１、Ｎｏ．２）、厚さ０．２６ｍｍ、保留粒子径５μｍ）を用いて濾過することにより得られた濾液の５０．０ｇを測り取り測定溶液とした。
【００９７】
はじめに０．５重量％ＮａＣｌ水溶液だけを、まず、０．１ＮのＮａＯＨ水溶液でｐＨ１０まで滴定を行い、その後、０．１ＮのＨＣｌ水溶液でｐＨ２．７まで滴定して空滴定量（［ｂＮａＯＨ］ｍｌ、［ｂＨＣｌ］ｍｌ）を得た。
同様の滴定操作を測定溶液についても行うことにより滴定量（［ＮａＯＨ］ｍｌ、［ＨＣｌ］ｍｌ）を求めた。
例えば既知量のアクリル酸とそのナトリウム塩からなる吸水剤の場合、そのモノマーの平均分子量と上記操作により得られた滴定量をもとに、吸水剤中の表層可溶分量を以下の計算式により算出することができる。未知量の場合は滴定により求めた中和率を用いてモノマーの平均分子量を算出する。
【００９８】
表層可溶分（重量％）＝０．１×（平均分子量）×１００×１００×(［ＨＣｌ］−［ｂＨＣｌ］)／１０００／０．５／５０．０
中和率（ｍｏｌ％）＝（１−（［ＮａＯＨ］−［ｂＮａＯＨ］）／（［ＨＣｌ］−［ｂＨＣｌ］））×１００
（８）中和指数
特開平１０−１０１７３５号およびその請求項３（欧州特許公開０８８２５０２号およびその請求項２〜４）に従い、以下、吸水性樹脂粉末および吸水剤の中和指数を求めた。
【００９９】
すなわち、ＪＩＳ標準篩で３００〜６００μｍに分級した吸水性樹脂粉末ないし吸水剤の粒子２００粒を、カバーガラスを貼りつけた２０ｍｍ×２０ｍｍの開口部を有する厚さ１．６ｍｍのプラスチックプレートに入れ、０．２ｍｌの脱イオン水を添加する。さらに、上記膨潤ゲルにブルムチモールブルー（ＢＴＢ）０．１重量％エタノール溶液とメチルレッド（ＭＲ）０．１重量％エタノール溶液との１．５：１混合溶液０．０５ｍｌをマイクロシリンジで添加して、ｐＨ指示薬によって粒子２００粒の着色を観察した。こうして吸水性樹脂ないし吸水剤の平均中和率から２０モル％を越えて不均一に中和された粒子の個数（２００個中で何個か）を求めて、この不均一な中和粒子の個数を中和指数（上記特許では第一中和指数／請求項３）として求めた。もちろん、中和指数が大きいほど、吸水性樹脂粉末の中和は不均一である。詳しくは、上記特許を参照。
【０１００】
（製造例１）：吸水性樹脂粉末（Ａ）の製造／中和重合
シグマ型羽根を２本有する内容積１０リットルのジャケット付きステンレス型双腕型ニーダーに蓋を付けて形成した反応器中で、７５モル％の中和率を有するアクリル酸ナトリウムの水溶液５５００ｇ（単量体濃度３８重量％、モノマーの平均分子量８８．５）にポリエチレングリコールジアクリレート（ｎ＝９）３．７０ｇを溶解させて反応液とした。次にこの反応液を窒素ガス雰囲気下で、３０分間脱気した。続いて、反応液に１０重量％過硫酸ナトリウム水溶液２８．３ｇおよび１重量％Ｌ−アスコルビン酸水溶液２．１ｇを攪拌しながら添加したところ、およそ１分後に重合が開始した。そして、生成したゲルを粉砕しながら、２０〜９５℃で重合を行い、重合が開始して３０分後に含水ゲル状架橋重合体（１）を取り出した。
【０１０１】
得られた含水ゲル状架橋重合体（１）は、その径が約５ｍｍ以下に細分化されていた。この細分化された含水ゲル状架橋重合体（１）を５０メッシュ（目開き３００μｍ）の金網上に広げ、１５０℃で９０分間熱風乾燥した。次いで、ロールミルを用いて粉砕し、さらに目開き８５０μｍおよび１０６μｍのＪＩＳ標準篩で分級することで大部分の粒子が８５０μｍ〜１０６μｍの範囲にある吸水性樹脂粉末（Ａ）を得た。
得られた吸水性樹脂粉末（Ａ）の無加圧下の吸収倍率は４９（ｇ／ｇ）、可溶分量は２３重量％、重量平均粒径（Ｄ５０）は３３０μｍ、８５０μｍ〜１５０μｍの範囲にある吸水性樹脂粉末は９７重量％であった。
【０１０２】
（製造例２）：吸水性樹脂粉末（Ｂ）の製造／中和重合
シグマ型羽根を２本有する内容積１０リットルのジャケット付きステンレス型双腕型ニーダーに蓋を付けて形成した反応器中で、７１モル％の中和率を有するアクリル酸ナトリウムの水溶液５５００ｇ（単量体濃度４１重量％、モノマーの平均分子量８７．７）にポリエチレングリコールジアクリレート（ｎ＝９）８．０５ｇを溶解させて反応液とした。次にこの反応液を窒素ガス雰囲気下で、３０分間脱気した。続いて、反応液に１０重量％過硫酸ナトリウム水溶液３０．８ｇおよび１重量％Ｌ−アスコルビン酸水溶液２．５７ｇを攪拌しながら添加したところ、およそ１分後に重合が開始した。そして、生成したゲルを粉砕しながら、２０〜９５℃で重合を行い、重合が開始して３０分後に含水ゲル状架橋重合体（２）を取り出した。
【０１０３】
得られた含水ゲル状架橋重合体（２）は、その径が約５ｍｍ以下に細分化されていた。この細分化された含水ゲル状架橋重合体（２）を５０メッシュ（目開き３００μｍ）の金網上に広げ、１８０℃で５０分間熱風乾燥した。次いで、ロールミルを用いて粉砕し、さらに目開き８５０μｍのＪＩＳ標準篩で分級することで大部分の粒子が８５０μｍ以下の範囲にある吸水性樹脂粉末（Ｂ）を得た。
得られた吸水性樹脂粉末（Ｂ）の無加圧下の吸収倍率は３６（ｇ／ｇ）、可溶分量は１０重量％、重量平均粒径（Ｄ５０）は４５０μｍ、８５０μｍ〜１５０μｍの範囲にある吸水性樹脂粉末は９７重量％であった。
【０１０４】
（製造例３）：吸水性樹脂粉末（Ｃ）の製造例／中和重合
製造例２において、ポリエチレングリコールジアクリレート５．０１ｇに変更した以外は製造例２と同様にして重合、乾燥、粉砕および分級を行い、吸水性樹脂粉末（Ｃ）を得た。得られた吸水性樹脂粉末（Ｃ）の無加圧下の吸収倍率は３９（ｇ／ｇ）、可溶分量は１３重量％、重量平均粒径（Ｄ５０）は４５０μｍ、８５０μｍ〜１５０μｍの範囲にある吸水性樹脂粉末は９７重量％であった。
（製造例４）：吸水性樹脂粉末（Ｄ）の製造例／中和重合
製造例２において、ポリエチレングリコールジアクリレート５．０１ｇに変更した以外は製造例２と同様にして重合、乾燥、および粉砕を行った。得られた粉砕物をさらに目開き６００μｍおよび３００μｍのＪＩＳ標準篩で分級することで、６００μｍ〜３００μｍの範囲にある吸水性樹脂粉末（Ｄ）を得た。得られた吸水性樹脂粉末（Ｄ）の無加圧下の吸収倍率は４０（ｇ／ｇ）、可溶分量は９重量％、重量平均粒径（Ｄ５０）は４５０μｍであった。
【０１０５】
（参考例１）：吸水性樹脂粉末（Ａ）の架橋処理／水溶性無機塩基あり
製造例１で得られた吸水性樹脂粉末（Ａ）１００ｇにエチレングリコールジグリシジルエーテル（デナコールＥＸ−８１０、ナガセ化成（株）社製）０．０２７ｇ、プロピレングリコール０．９ｇ、水２．７ｇ及び炭酸水素ナトリウム０．１８ｇの混合液からなる表面処理剤を混合した後、混合物を２１０℃で３５分間加熱処理することにより、吸水剤（１）を得た。得られた吸水剤（１）も粉末状であり、その無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。
【０１０６】
（参考例２）：吸水性樹脂粉末（Ａ）の架橋処理／水溶性無機塩基あり
参考例１において、炭酸水素ナトリウムを用いる代わりに、炭酸ナトリウムを０．０９ｇ用いた以外は同様にして、吸水剤（２）を得た。無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。
（比較例１）：吸水性樹脂粉末（Ａ）の架橋処理／水溶性無機塩基なし
参考例１において、炭酸水素ナトリウムを用いる代わりに、イソプロピルアルコール０．８１ｇを用いた以外は同様にして、比較用吸水剤（１）を得た。無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。
【０１０７】
（比較例２）：吸水性樹脂粉末（Ａ）の架橋処理／水溶性無機塩基なし
参考例１において、炭酸水素ナトリウムを用いなかった以外は同様にして、比較用吸水剤（２）を得た。無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。
（参考例３）：吸水性樹脂粉末（Ｂ）の架橋処理／水溶性無機塩基あり
製造例２で得られた吸水性樹脂粉末（Ｂ）１００ｇに１，４−ブタンジオール０．３８４ｇ、プロピレングリコール０．６ｇ、水３．２８ｇ、および２４重量％水酸化ナトリウム水溶液０．３ｇ（固形分０．０７２ｇ）の混合液からなる表面処理剤を混合した後、混合物を２１２℃で３０分間加熱処理することにより、吸水剤（３）を得た。得られた吸水剤（３）も粉末形状であり、その無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。
【０１０８】
（比較例３）：吸水性樹脂粉末（Ｂ）の架橋処理／水溶性無機塩基なし
参考例３において、２４重量％水酸化ナトリウム水溶液を用いなかった以外は同様にして、比較用吸水剤（３）を得た。無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。
（参考例４）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基あり
製造例３で得られた吸水性樹脂粉末（Ｃ）１００ｇに１，４−ブタンジオール０．３８４ｇ、プロピレングリコール０．６ｇ、水３．２８ｇ、および炭酸水素ナトリウム０．２４ｇの混合液からなる表面処理剤を混合した後、混合物を２１２℃で４０分間加熱処理することにより、吸水剤（４）を得た。得られた吸水剤（４）も粉末形状であり、その無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。
【０１０９】
（参考例５）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基あり
参考例４において、炭酸水素ナトリウムを用いる代わりに、炭酸ナトリウム０．１２ｇを用いた以外は同様にして、吸水剤（５）を得た。無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。
（参考例６）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基あり
参考例４において、炭酸水素ナトリウムを用いる代わりに、２４重量％水酸化ナトリウム水溶液０．３ｇ（固形分０．０７２ｇ）を用いた以外は同様にして、吸水剤（６）を得た。無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。
【０１１０】
（比較例４）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基なし
参考例４において、炭酸水素ナトリウムを用いなかった以外は同様にして、比較用吸水剤（４）を得た。無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。
（参考例７）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基あり
参考例４において、加熱処理時間を３０分間にした以外は同様にして、吸水剤（７）を得た。無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。
【０１１１】
（参考例８）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基あり
参考例７において、炭酸水素ナトリウムを用いる代わりに、炭酸ナトリウム０．１２ｇを用いた以外は同様にして、吸水剤（８）を得た。無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。
（参考例９）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基あり
参考例７において、炭酸水素ナトリウムを用いる代わりに、２４重量％水酸化ナトリウム水溶液０．３ｇ（固形分０．０７２ｇ）を用いた以外は同様にして、吸水剤（９）を得た。無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。また、吸水剤（９）の表層可溶分は３．８重量％であった。
【０１１２】
（比較例５）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基なし
参考例７において、炭酸水素ナトリウムを用いなかった以外は同様にして、比較用吸水剤（５）を得た。無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表１に示した。また、比較用吸水剤（５）の表層可溶分は６．５重量％であった。
（比較例６）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基なし
参考例９において、２４重量％水酸化ナトリウム水溶液の代わりに、ＷＯ００／５３６６４に準じて、硫酸アルミニウム１４〜１８水和物を０．４５５ｇ用いた以外は同様にして、比較用吸水剤（６）を得た。その結果を表１に示した。
【０１１３】
（参考例１０）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基あり
製造例３で得られた吸水性樹脂粉末（Ｃ）１００ｇにエチレングリコールジグリシジルエーテル（デナコールＥＸ−８１０、ナガセ化成（株）社製）０．７８４ｇ、水４．０ｇ、および２４重量％水酸化ナトリウム水溶液０．５ｇ（固形分０．１２ｇ）の混合液からなる表面処理剤を混合した後、混合物を２１２℃で４０分間加熱処理することにより、吸水剤（１０）を得た。得られた吸水剤（１０）も粉末形状であり、結果を表１に示した。
（比較例７）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基なし
参考例１０において、２４重量％水酸化ナトリウム水溶液を用いなかった以外は同様にして、比較用吸水剤（７）を得た。その結果を表１に示した。
【０１１４】
（参考例１１）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基あり
製造例３で得られた吸水性樹脂粉末（Ｃ）１００ｇに３−エチル−３−オキセタンメタノール０．４ｇ、水３．０ｇ、および２４重量％水酸化ナトリウム水溶液０．３ｇ（固形分０．０７２ｇ）の混合液からなる表面処理剤を混合した後、混合物を２１２℃で４０分間加熱処理することにより、吸水剤（１１）を得た。得られた吸水剤（１１）も粉末形状であり、その結果を表１に示した。
（比較例８）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基なし
参考例１１において、２４重量％水酸化ナトリウム水溶液を用いなかった以外は同様にして、比較用吸水剤（８）を得た。その結果を表１に示した。
【０１１５】
（実施例１）：吸水性樹脂粉末（Ｃ）の架橋処理／ｐＨ緩衝剤あり
製造例３で得られた吸水性樹脂粉末（Ｃ）１００ｇにエチレングリコールジグリシジルエーテル（デナコールＥＸ−８１０、ナガセ化成製）０．１５ｇ、プロピレングリコール１．０ｇ、水５．０ｇ、およびリン酸２水素ナトリウム・２水和物０．５ｇの混合液からなる表面処理剤を混合した後、混合物を１５０℃で３０分間加熱処理することにより、吸水剤（１２）を得た。得られた吸水剤（１２）も粉末形状であり、その結果を表１に示した。
（比較例９）：吸水性樹脂粉末（Ｃ）の架橋処理／ｐＨ緩衝剤なし
実施例１において、リン酸二水素ナトリウム二水和物を用いなかった以外は同様にして、比較用吸水剤（９）を得た。その結果を表１に示した。
【０１１６】
（参考例１２）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基あり
参考例９において、同様の手法を用いて、吸水剤（１３）を得た。得られた吸水剤（１３）に前記の機械的ダメージを１０分間与えた後、得られた吸水剤（１３）の無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表２に示した。さらに得られた吸水剤（１３）を、ＪＩＳ標準ふるい（目開き８５０μｍ、６００μｍ、５００μｍ、３００μｍ、１５０μｍ）でふるい、それぞれ、８５０μｍ未満で６００μｍ以上の粒子（１３−ａ）、粒子径が６００μｍ未満で５００μｍ以上の粒子（１３−ｂ）、粒子径が５００μｍ未満で３００μｍ以上の粒子（１３−ｃ）、粒子径が３００μｍ未満で１５０μｍ以上の粒子（１３−ｄ）を得た。得られた吸水剤（１３−ａ）、（１３−ｂ）、（１３−ｃ）、（１３−ｄ）を測定した結果を表２に示した。また、ＳＦＣ変化指数、ＳＦＣ変動係数、ＳＦＣ変動率を算出した結果を表３に示した。
【０１１７】
（参考例１３）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基あり
参考例９において、加熱時間を２０分間にした以外は同様の手法をもちいて吸水剤（１４）を得た。得られた吸水剤（１４）に前記の機械的ダメージを１０分間与えた後、得られた吸水剤（１４）を測定した結果を表２に示した。さらに得られた吸水剤（１４）を、ＪＩＳ標準ふるい（目開き８５０μｍ、６００μｍ、５００μｍ、３００μｍ、１５０μｍ）でふるい、それぞれ、８５０μｍ未満で６００μｍ以上の粒子（１４−ａ）、粒子径が６００μｍ未満で５００μｍ以上の粒子（１４−ｂ）、粒子径が５００μｍ未満で３００μｍ以上の粒子（１４−ｃ）、粒子径が３００μｍ未満で１５０μｍ以上の粒子（１４−ｄ）を得た。得られた吸水剤（１４−ａ）、（１４−ｂ）、（１４−ｃ）、（１４−ｄ）を測定した結果を表２に示した。また、ＳＦＣ変化指数、ＳＦＣ変動係数、ＳＦＣ変動率を算出した結果を表３に示した。
【０１１８】
（比較例１０）：吸水性樹脂粉末（Ｃ）の架橋処理／水溶性無機塩基なし
比較例５において、同様の手法を用いて、比較用吸水剤（１０）を得た。得られた比較用吸水剤（１０）に機械的ダメージを１０分間与えた後、得られた比較用吸水剤（１０）の無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表２に示した。さらに得られた比較用吸水剤（１０）を、ＪＩＳ標準ふるい（目開き８５０μｍ、６００μｍ、５００μｍ、３００μｍ、１５０μｍ）でふるい、それぞれ、８５０μｍ未満で６００μｍ以上の粒子（１０−ａ）、粒子径が６００μｍ未満で５００μｍ以上の粒子（１０−ｂ）、粒子径が５００μｍ未満で３００μｍ以上の粒子（１０−ｃ）、粒子径が３００μｍ未満で１５０μｍ以上の粒子（１０−ｄ）を得た。得られた比較用吸水剤（１０−ａ）、（１０−ｂ）、（１０−ｃ）、（１０−ｄ）を測定した結果を表２に示した。また、ＳＦＣ変化指数、ＳＦＣ変動係数、ＳＦＣ変動率を算出した結果を表３に示した。
【０１１９】
（比較例１１）：市販品の吸水剤
ドイツで市販されているＰａｍｐｅｒｓ Ａｃｉｔｖｅ Ｆｉｔ（Ｐ＆Ｇ社製、２００１年１２月５日購入）のおむつから吸水剤を取り出し、比較用吸水剤（１１）を得た。得られた比較用吸水剤（１１）の無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表２に示した。さらに得られた比較用吸水剤（１１）を、ＪＩＳ標準ふるい（目開き８５０、６００、５００、３００、１５０μｍ）でふるい、それぞれ、８５０μｍ未満で６００μｍ以上の粒子（１１−ａ）、粒子径が６００μｍ未満で５００μｍ以上の粒子（１１−ｂ）、粒子径が５００μｍ未満で３００μｍ以上の粒子（１１−ｃ）、粒子径が３００μｍ未満で１５０μｍ以上の粒子（１１−ｄ）を得た。得られた吸水剤（１１−ａ）、（１１−ｂ）、（１１−ｃ）、（１１−ｄ）を測定した結果を表２に示した。また、ＳＦＣ変化指数、ＳＦＣ変動係数、ＳＦＣ変動率を算出した結果を表３に示した。
【０１２０】
（比較例１２）：市販品の吸水剤
日本で市販されていた「パンパースさらさらケア」（Ｐ＆Ｇ社製、１９９７年１２月購入）のおむつから吸水剤を取り出し、比較用吸水剤（１２）とした。比較吸水剤（１２）の無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表２に示した。
さらに得られた比較用吸水剤（１２）をＪＩＳ標準ふるい（目開き８５０、６００、５００、３００、１５０μｍ）でふるい、それぞれ、８５０μｍ未満で６００μｍ以上の粒子（１２−ａ）、粒子径が６００μｍ未満で５００μｍ以上の粒子（１２−ｂ）、粒子径が５００μｍ未満で３００μｍ以上の粒子（１２−ｃ）、粒子径が３００μｍ未満で１５０μｍ以上の粒子（１２−ｄ）を得た。得られた吸水剤（１２−ａ）、（１２−ｂ）、（１２−ｃ）、（１２−ｄ）の無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表２に示した。また、ＳＦＣ変化指数、ＳＦＣ変動係数、ＳＦＣ変動率を算出した結果を表３に示した。
【０１２１】
（参考例１４）：吸水性樹脂粉末（Ｄ）の架橋処理／水溶性無機塩基あり
製造例４で得られた吸水性樹脂粉末（Ｄ）１００ｇに１，４−ブタンジオール０．３８４ｇ、プロピレングリコール０．６ｇ、水３．２８ｇ、および２４重量％水酸化ナトリウム水溶液０．３ｇ（固形分０．０７２ｇ）の混合液からなる表面処理剤を混合した後、混合物を２１２℃で２０分間加熱処理することにより、吸水剤（１５）を得た。得られた吸水剤（１５）に前記の機械的ダメージを１０分間与えた後、得られた吸水剤（１５）を測定した結果を表２に示した。さらに得られた吸水剤（１５）を、ＪＩＳ標準ふるい（目開き８５０μｍ、６００μｍ、５００μｍ、３００μｍ、１５０μｍ）でふるい、それぞれ、粒子径が６００μｍ未満で５００μｍ以上の粒子（１５−ｂ）、粒子径が５００μｍ未満で３００μｍ以上の粒子（１５−ｃ）を得た。得られた吸水剤（１５−ｂ）、（１５−ｃ）を測定した結果を表２に示した。また、ＳＦＣ変化指数、ＳＦＣ変動係数、ＳＦＣ変動率を算出した結果を表３に示した。
【０１２２】
（参考例１５）：吸水性樹脂粉末（Ｄ）の架橋処理／水溶性無機塩基あり
参考例１４において、加熱時間を４０分間にした以外は同様にして、吸水剤（１６）を得た。得られた吸水剤（１６）に前記の機械的ダメージを１０分間与えた後、得られた吸水剤（１６）を測定した結果を表２に示した。さらに得られた吸水剤（１６）を、ＪＩＳ標準ふるい（目開き８５０μｍ、６００μｍ、５００μｍ、３００μｍ、１５０μｍ）でふるい、それぞれ、粒子径が６００μｍ未満で５００μｍ以上の粒子（１６−ｂ）、粒子径が５００μｍ未満で３００μｍ以上の粒子（１６−ｃ）を得た。得られた吸水剤（１６−ｂ）、（１６−ｃ）を測定した結果を表２に示した。また、ＳＦＣ変化指数、ＳＦＣ変動係数、ＳＦＣ変動率を算出した結果を表３に示した。
【０１２３】
（比較例１３〜１６）：市販品の吸水剤
実使用されている吸水剤（吸水性樹脂）として、２００１年に市販の紙おむつより吸水性樹脂を取り出し比較吸水剤（１３）〜（１６）とした。比較吸水剤（１３）〜（１６）の無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性を測定した結果を表４に示した。
（製造例５）：吸水性樹脂粉末（Ｅ）の製造／酸型重合で後中和
２Ｌのプラスチック容器にアクリル酸２５２．２ｇ、Ｎ，Ｎ’−メチレンビスアクリルアミド１．１ｇ、水９９８．４ｇを混合し反応液とした。次にこの反応液を窒素ガス雰囲気下で、３０分間脱気した。続いて、反応液に１５重量％２，２’−アゾビス（２−アミジノプロパン）二塩酸塩５．１ｇ、１０重量％Ｌ−アスコルビン酸水溶液０．６３ｇ、および７重量％過酸化水素水溶液３．６ｇを加えて重合を開始させた。１６〜７４℃で重合を行い、重合が開始してから３時間後に含水ゲル状架橋重合体（５）を取り出した。得られた重合体（５）を約５ｃｍ角に切断してからその１０００ｇについて、中和率が６５モル％となる量の４８重量％の水酸化ナトリウム水溶液１５．０ｇを混合し、さらにダイス径９．５ｍｍのミートチョッパーに通して細分化された粉砕ゲルとした。得られた粉砕ゲルを５０メッシュ（目開き３００μｍ）の金網上に広げ、１７０℃で４０分間熱風乾燥した。次いで、ロールミルを用いて粉砕し、さらに目開き５００μｍおよび３００μｍのＪＩＳ標準網で分級することで大部分の粒子が５００μｍ〜３００μｍの範囲にある吸水性樹脂粉末（Ｅ）を得た。得られた吸水性樹脂粉末（Ｅ）の無加圧下の吸収倍率は４９（ｇ／ｇ）、可溶分量は６重量％であった。
【０１２４】
さらに得られた粒子の中和率の均一性を調べるために、２００個の粒子を膨潤させ、さらに、ｐＨ指示薬であるブロモチモールブルーとメチルレッドの０．１重量％エタノール溶液を添加し中和指数（特開平１０−１０１７３５号の請求項３）を測定した。その結果、製造例１、６、７で得られた中和重合から得られた吸水性樹脂粉末（Ａ）、（Ｆ）、（Ｇ）は２００個の粒子が一様に黄色（中和指数が０）であるのに対して、吸水性樹脂粉末（Ｅ）の粒子は濃緑色から赤色まで様々な色に発色する粒子が混在し、個々の粒子の中和率が非常に不均一（中和指数が１５以上）であった。
【０１２５】
（製造例６）：吸水性樹脂粉末（Ｆ）の製造例／中和重合
製造例１において、単量体濃度を３９重量％、中和率を７１モル％、ポリエチレングリコールジアクリレート９．６ｇに変更した以外は製造例１と同様にして重合、乾燥および粉砕を行った。得られた粉砕物をさらに目開き５００μｍおよび３００μｍのＪＩＳ標準篩で分級することで大部分の粒子が５００μｍ〜３００μｍの範囲にある吸水性樹脂粉末（Ｆ）を得た。得られた吸水性樹脂粉末（Ｆ）の無加圧下の吸収倍率は３２（ｇ／ｇ）、可溶分量は１０重量％であった。
（製造例７）：吸水性樹脂粉末（Ｇ）の製造例／中和重合
製造例１において、単量体濃度を４１重量％、中和率を７１モル％、ポリエチレングリコールジアクリレート５．４７ｇ、過硫酸ナトリウム水溶液３０．８ｇ、Ｌ−アスコルビン酸水溶液２．５７ｇ、熱風乾燥温度１８０℃、熱風乾燥時間５０分間に変更した以外は製造例１と同様にして重合、乾燥および粉砕を行った。得られた粉砕物をさらに目開き８５０μｍのＪＩＳ標準篩で分級することで大部分の粒子が８５０μｍ以下の範囲にある吸水性樹脂粉末（Ｇ）を得た。
【０１２６】
得られた吸水性樹脂粉末（Ｇ）の無加圧下の吸収倍率は３８（ｇ／ｇ）、可溶分量は１３重量％、重量平均粒径（Ｄ５０）は４００μｍであった。
（実施例２）：吸水性樹脂粉末（Ｅ）の架橋処理／ｐＨ緩衝剤あり
製造例５で得られた吸水性樹脂粉末（Ｅ）１００ｇにエチレングリコールジグリシジルエーテル（デナコールＥＸ−８１０、ナガセ化成（株）社製）０．５ｇ、プロピレングリコール１．０ｇ、中性リン酸塩ｐＨ標準液（リン酸二水素カリウム／リン酸水素二ナトリウム；ｐＨ６．８６）６．０ｇ、およびイソプロピルアルコール１．０ｇの混合液からなる表面処理剤を混合した後、混合物を１２０℃で３０分間加熱処理することにより、吸水剤（１７）を得た。得られた吸水剤（１７）も粉末形状であり、その無加圧下吸収倍率、加圧下吸収倍率を測定した結果を表５に示した。
【０１２７】
（比較例１７）：吸水性樹脂粉末（Ｅ）の架橋処理／ｐＨ緩衝剤なし
実施例２において、中性リン酸塩ｐＨ標準液の代わりに水６．０ｇを用いた以外は同様にして比較用吸水剤（１７）を得た。無加圧下吸収倍率、加圧下吸収倍率を測定し、その結果を表５に示した。
（実施例３）：吸水性樹脂粉末（Ｆ）の架橋処理／ｐＨ緩衝剤あり
製造例６で得られた吸水性樹脂粉末（Ｆ）１００ｇに１，４−ブタンジオール０．３２ｇ、プロピレングリコール０．５ｇ、水２．７３ｇ、リン酸二水素ナトリウム二水和物１．２ｇの混合液からなる表面処理剤を混合した後、混合物を１９７℃で１０分加熱処理することにより吸水剤（１８）を得た。得られた吸水剤（１８）も粉末形状であり、その無加圧下吸収倍率、加圧下吸収倍率を測定した結果を表５に示した。
【０１２８】
（比較例１８）：吸水性樹脂粉末（Ｆ）の架橋処理／ｐＨ緩衝剤なし
実施例３において、リン酸二水素ナトリウム二水和物の代わりにリン酸（８５重量％）０．６ｇを用いた以外は同様にして比較用吸水剤（１８）を得た。無加圧下吸収倍率、加圧下吸収倍率を測定した結果を表５に示した。
（比較例１９）：吸水性樹脂粉末（Ｆ）の架橋処理／ｐＨ緩衝剤なし
実施例３において、リン酸二水素ナトリウム二水和物を用いなかった以外は同様にして比較用吸水剤（１９）を得た。無加圧下吸収倍率、加圧下吸収倍率を測定した結果を表５に示した。
【０１２９】
（実施例４）：吸水性樹脂粉末（Ｇ）の架橋処理／ｐＨ緩衝剤あり
製造例７で得られた吸水性樹脂粉末（Ｇ）１００ｇに１，４−ブタンジオール０．３２ｇ、プロピレングリコール０．５ｇ、水２．７３ｇ、および炭酸水素ナトリウム０．２ｇの混合液からなる表面処理剤溶液を混合した後、混合物を２１２℃で２５分間加熱処理することにより、吸水剤（１９）を得た。無加圧下吸収倍率、加圧下吸収倍率を測定した結果を表５に示した。
（実施例５）：吸水性樹脂粉末（Ｇ）の架橋処理／ｐＨ緩衝剤あり
製造例７で得られた吸水性樹脂粉末（Ｇ）１００ｇに１，４−ブタンジオール０．３２ｇ、プロピレングリコール０．５ｇ、水２．７３ｇ、および炭酸水素カリウム０．２４ｇの混合液からなる表面処理剤溶液を混合した後、混合物を２１２℃で２５分間加熱処理することにより、吸水剤（２０）を得た。無加圧下吸収倍率、加圧下吸収倍率を測定した結果を表５に示した。
【０１３０】
（比較例２０）：吸水性樹脂粉末（Ｇ）の架橋処理／ｐＨ緩衝剤なし
実施例４において、炭酸水素ナトリウムを用いなかった以外は同様にして比較用吸水剤（２０）を得た。無加圧下吸収倍率、加圧下吸収倍率を測定した結果を表５に示した。
（参考例１６）：連続生産系
７１モル％が中和されたアクリル酸部分ナトリウム塩とポリエチレングリコールジアクリレート（ｎ＝９）を製造例３の比率で、連続的に水溶液重合（ベルト滞留時間：約３０分、厚み：約２５ｍｍ）し、得られた吸水性樹脂の含水ゲル状架橋重合体をミートチョッパーで粒子状に粗砕し、これをバンド乾燥機の多孔板上に薄く広げて載せ、１８０℃で３０分間連続熱風乾燥した。乾燥機出口でブロック状の乾燥重合体が得られた。この乾燥重合体を取り出したと同時に解砕し、得られた粒子状乾燥物を１０００ｋｇ／ｈで３段ロールグラニュレーター（ロールギャップが上から１．０ｍｍ／０．５５ｍｍ／０．４２ｍｍ）に連続供給することで粉砕した。得られた約６０℃の粒子状吸水性樹脂の粉末を、網目開き８５０μｍのふるい網を有する篩い分け装置で分級し、９０重量％以上が８５０μｍ未満で１５０μｍ以上のサイズの吸水性樹脂粉末（Ｈ）（平均粒子径：４３０〜４６０μｍ）を得た。得られた吸水性樹脂粉末（Ｈ）の無加圧下の平均吸収倍率（ＣＲＣ）は４０ｇ／ｇ、可溶分量の平均は１１重量％であった。なお、ＣＲＣおよび可溶分量の物性は２時間ごと（２０００ｋｇ／Ｌｏｔ）に測定した平均値である。
【０１３１】
さらに、吸水性樹脂粉末（Ｈ）を、高速連続混合機（タービュライザー／１０００ｒｐｍ）に１０００ｋｇ／ｈで連続供給して、さらに、吸水性樹脂粉末（Ｈ）に１，４−ブタンジオール／プロピレングリコール／水／２４％水酸化ナトリウム水溶液＝０．３８４／０．６３／３．３９／０．３（重量％／対粉末）からなる表面架橋剤水溶液を、約２００μｍの液滴になるスプレーで噴霧し混合した。次いで、得られた混合物を１９５℃で４０分間、パドルドライヤーにより連続的に加熱処理することで吸水剤粉末を得た。さらに得られた吸水剤粉末を、網目開き８５０μｍのふるい網を有する篩い分け装置で分級して、８５０μｍ未満で１５０μｍ以上のサイズの粒子が９０重量％以上の吸水剤（２１）を得た。
【０１３２】
前記の一連の工程（重合、乾燥、粉砕、加熱処理）を連続で２４時間で行い、２時間ごと（２０００ｋｇ／Ｌｏｔ）に吸水剤の物性（Ｌｏｔ数：１１点）を測定した結果、無加圧下の吸収倍率の平均値は３１．１ｇ／ｇ、加圧下での吸収倍率の平均値は２５．５ｇ／ｇ、生理食塩水流れ誘導性の平均値は３０（Ｌｏｔ毎のＳＦＣの値：３２、３２、２８、２８、３０、２７、２７、３２、３１、３２、２８）、そのＳＦＣの標準偏差の値は２．１であった。
（参考例１７）：連続生産系
参考例１６において、２４時間を１０日間に変えた以外は同様の方法で連続生産を行い、吸水剤（２２）を得た。２時間ごと（２０００ｋｇ／Ｌｏｔ）に吸水剤の物性（Ｌｏｔ数：１１０点）を測定した結果、無加圧下の吸収倍率の平均値は３１．３ｇ／ｇ、加圧下での吸収倍率の平均値は２５．２ｇ／ｇ、生理食塩水流れ誘導性の平均値は３０（Ｌｏｔ毎のＳＦＣの値は省略）、そのＳＦＣの標準偏差の値は３．９であった。
【０１３３】
（比較例２１）：連続生産系
参考例１６において、２４％水酸化ナトリウム水溶液を使わなかった以外は同様の方法で連続生産を行い、比較用吸水剤（２１）を得た。２時間ごと（２０００ｋｇ／Ｌｏｔ）に吸水剤の物性（Ｌｏｔ数：１１点）を測定した結果、無加圧下の吸収倍率の平均値は３１．１ｇ／ｇ、加圧下での吸収倍率の平均値は２４．２ｇ／ｇ、生理食塩水流れ誘導性の平均値は２０（Ｌｏｔ毎のＳＦＣの値：２６、１７、１１、１７、１７、１８、２０、１７、１６、２８、２８）、そのＳＦＣの標準偏差の値は５．５であった。
【０１３４】
参考例１６および参考例１７に記載の吸水剤（２１）、（２２）は、比較例２１に記載の比較用吸水剤（２１）に比べて、ＳＦＣの標準偏差が小さくなり、本発明の吸水剤を連続生産する場合、不良品（低ＳＦＣ品など）の発生もなく、かつ、品質（ＳＦＣ）のばらつきが低減されることを示している。
【０１３５】
【表１】

【０１３６】
【表２】

【０１３７】
【表３】

【０１３８】
参考例１および参考例２に記載の吸水剤（１）、（２）は、同じく表面架橋された比較用吸水剤（１）、（２）と比べて、加圧下吸収倍率が大きく、無加圧下吸収倍率と加圧下吸収倍率のバランスに優れている。
参考例３に記載の吸水剤（３）は、比較例３に記載の比較用吸水剤（３）と比べて、無加圧下吸収倍率と加圧下吸収倍率と生理食塩水流れ誘導性の３つのバランスに優れている。
さらに、参考例４および参考例５および参考例６に記載の吸水剤（４）、（５）、（６）は、比較例４に記載の比較用吸水剤（４）と比べて、無加圧下吸収倍率はほぼ同じであるが生理食塩水流れ誘導性は高い値を示している。
【０１３９】
同様に、参考例７および参考例８および参考例９に記載の吸水剤（７）（８）（９）においても、比較例５および比較例６に記載の比較用吸水剤（５）および比較用吸水剤（６）と比べて、無加圧下吸収倍率はほぼ同じであるが、加圧下吸水倍率と生理食塩水流れ誘導性は高い値を示している。
また、参考例１０、参考例１１、実施例１に記載の吸水剤（１０）、（１１）、（１２）は、それぞれ比較例７、比較例８、比較例９に記載の比較用吸水剤（７）、（８）、（９）と比べて、無加圧下吸収倍率はほぼ同じであるが、生理食塩水流れ誘導性は高い値を示している。
【０１４０】
参考例１２および参考例１３に記載の吸水剤（１３）、（１４）は、比較例１０および比較例１１および比較例１２に記載の比較用吸水剤（１０）、（１１）、（１２）と比べて、ＳＦＣ変化指数およびＳＦＣ変動係数は小さく、ＳＦＣ変動率は大きくなりいずれもＳＦＣのばらつきが低減されている。
また、参考例１４および参考例１５に記載の吸水剤（１５）、（１６）も、ＳＦＣ変化指数およびＳＦＣ変動指数は小さく、ＳＦＣ変動率は大きくなり、いずれもＳＦＣのばらつきが低減されている。
このように、本発明の方法で製造される吸水剤は、無加圧下吸収倍率と加圧下吸収倍率と生理食塩水流れ誘導性の３つのバランスに優れ、良好な性能を備えたものである。さらに、粒度毎のＳＦＣのばらつきも少ない事から、おむつの性能を安定させる上で非常に優れた吸水剤である。
【０１４１】
【表４】

【０１４２】
比較例１３、比較例１４、比較例１５、比較例１６に記載の比較用吸水剤（１３）、（１４）、（１５）、（１６）は、いずれも無加圧下吸収倍率と加圧下吸収倍率と生理食塩水流れ誘導性の３つのバランスが悪いものであった。
【０１４３】
【表５】

【０１４４】
実施例２記載の吸水剤（１７）は、比較例１７記載の比較用吸水剤（１７）と比べて、無加圧下吸収倍率と加圧下吸収倍率のバランスやその合計に優れている。
また、実施例３記載の吸水剤（１８）は、リン酸を加えた比較例１８記載の比較用吸水剤（１８）と比べて、同様に１０分という短い時間で架橋反応が進行し、無加圧下吸収倍率は同じであるが加圧下吸収倍率は高い値を示している。さらに、何も加えなかった比較例１９記載の比較用吸水剤（１９）については、１０分という短時間では十分な架橋反応が進行せず、無加圧下吸収倍率の低下がほとんど見られず、加圧下吸収倍率も低いものとなっている。
【０１４５】
このように、本発明の方法で製造される吸水剤は、無加圧下吸収倍率と加圧下吸収倍率のバランスやその合計に優れ、短い反応時間でも良好な性能を備えたものである。
【０１４６】
【発明の効果】
本発明によれば、架橋処理時に、混合助剤としての効果を示しながらも架橋反応を阻害せず、場合によっては反応触媒としての効果も併せ持ち、かつ部分中和重合された吸水性樹脂の中和率の違いや酸型重合の後中和操作に起因する中和率の均一性にほとんど関わりなく、均一な表面架橋が発現でき、無加圧下吸収倍率、加圧下吸収倍率、生理食塩水流れ誘導性のバランスに優れるとともに、製造の際のロットごと、あるいは各ロット中における生理食塩水流れ誘導性の値の振れ（バラツキ）が小さい、物性の安定した吸水剤を短時間で製造する方法および吸水剤を提供することができる。
【図面の簡単な説明】
【図１】生理食塩水流れ誘導性の測定に用いる測定装置の概略の断面図。
【図２】機械的ダメージ試験に用いるガラス製容器の側面概略図（ａ）と平面概略図（ｂ）。
【図３】機械的ダメージ試験に用いる分散機の概略図。
【符号の説明】
３１ タンク
３２ ガラス管
３３ ０．６９重量％塩化ナトリウム水溶液
３４ コック付きＬ字管
３５ コック
４０ 容器
４１ セル
４２ ステンレス製金網
４３ ステンレス製金網
４４ 膨潤ゲル
４５ ガラスフィルター
４６ ピストン
４７ ピストン中の穴
４８ 補集容器
４９ 上皿天秤
５１ ガラス容器
５２ 分散機
５３ 上側クランプ
５４ 下側クランプ[0001]
BACKGROUND OF THE INVENTION
  The present invention absorbs waterMedicinalIt relates to a manufacturing method. More specifically, the present invention modifies the water absorbent resin with a crosslinking agent.so,A water-absorbing agent with high absorbency and high saline flow inductivity under no pressure or under pressureGetRegarding the method.
[0002]
[Prior art]
In recent years, hygienic materials such as paper diapers and sanitary napkins, so-called incontinence pads, have widely used water-absorbing resins (water-absorbing agents) for the purpose of absorbing body fluid.
Examples of the water-absorbing resin include a crosslinked polyacrylic acid partially neutralized product, a hydrolyzate of starch-acrylic acid graft polymer, a saponified vinyl acetate-acrylic ester copolymer, an acrylonitrile copolymer, or an acrylamide. A hydrolyzate of a copolymer or a crosslinked product thereof, and a crosslinked polymer of a cationic monomer are known.
[0003]
As the characteristics that the water-absorbent resin should have, water is absorbed from a substrate containing an aqueous liquid, an excellent liquid absorption amount, water absorption speed, gel strength, gel permeability, and aqueous liquid when conventionally in contact with an aqueous liquid such as a body fluid. The suction power to suck up is advocated. Various water-absorbing resins (water-absorbing agents) that have a combination of these characteristics and exhibit excellent performance (absorption characteristics) when used in sanitary materials such as paper diapers and sanitary napkins have been proposed. .
For example, as a method for improving the absorption characteristics of the water absorbent resin under no pressure and the absorption capacity under pressure in a well-balanced manner, a technique for crosslinking the vicinity of the surface of the water absorbent resin is known. Is disclosed.
[0004]
Examples thereof include a method using a polyhydric alcohol (Japanese Patent Laid-Open Nos. 58-180233 and 61-16903), a polyvalent glycidyl compound, a polyvalent aziridine compound, a polyvalent amine compound, and a polyvalent isocyanate compound. Method used (Japanese Patent Laid-Open No. 59-189103), method using glyoxal (Japanese Patent Laid-Open No. 52-117393), method using polyvalent metal (Japanese Patent Laid-Open No. 51-136588, Japanese Patent Laid-Open No. 61-257235) , JP-A-62-27455), a method using a silane coupling agent (JP-A-61-211305, JP-A-61-225212, JP-A-61-264006), alkylene Method using carbonate (German Patent No. 4020780), Method using polyvalent heterocyclic carbonate (JP-A-1 -315216), method using oxazolidinone (WO99 / 42494), method using polyvalent oxazolidinone (WO99 / 43720), method using oxazine (WO00 / 31153), method using oxazoline compound (JP No. 2000-197818) is known.
[0005]
Furthermore, a method of using an additive (inert mixing aid, acid catalyst, base) for further performance improvement when the absorption property is improved by the crosslinking agent is also known. That is, as a method (1) using an inert mixing aid as an additive, a method in which an inert inorganic powder is present (Japanese Patent Laid-Open Nos. 60-163156 and 60-255814), a polyvalent metal A method of allowing water containing a salt and / or a hydroxide to exist (Japanese Patent Laid-Open No. 62-7745), a method of causing a dihydric alcohol to be present (Japanese Patent Laid-Open No. 1-2292004), a method of causing water and an ether compound to exist (JP-A-2-153903), a method for allowing a water-soluble polymer to be present (JP-A-3-126730), a method for allowing an alkylene oxide adduct of a monohydric alcohol, a monovalent salt of an organic acid, or a lactam to exist. (Japanese Patent Publication No. 6-74331, Japanese Patent Application Laid-Open No. 7-33818), a method in which a monovalent metal salt is present (WO 98/49221), a cation Method of Zaisa (WO00 / 53664 discloses, WO00 / 53644 publication) are known.
[0006]
Further, as a method (2) using an acid catalyst as an additive, a method in which phosphoric acid is present (WO94 / 15651), a method in which an inorganic acid or an organic acid is present (JP-A-7-278225), and the like are known. It has been.
In addition, as a method (3) using a base as an additive, a method in which a water-soluble alkali compound is present (Japanese Patent Laid-Open No. Hei 6-298881) is also known.
The presence of the additive used in the methods (1), (2), and (3) together with the crosslinking agent can improve the balance of the absorption characteristics of the water-absorbing agent to some extent as compared with the crosslinking agent alone, but still more It was hard to say enough.
[0007]
That is, with the additive (inert mixing aid) used in the method (1), when the water-absorbing resin to be used contains a large amount of fine powder, its effect appears due to the action as a mixing aid. However, on the other hand, due to its presence, there is almost no improvement in the absorption characteristics due to excessive decrease in the permeability of the crosslinking agent to the water-absorbent resin powder, inhibition of the crosslinking reaction, etc. There are also problems that the reaction time increases, the reaction time becomes longer, the reaction temperature has to be raised, and the like.
The additive (acid catalyst) used in the method (2) can be expected to have an effect as a catalyst for promoting the reaction of the crosslinking agent. However, when an amount for obtaining a certain effect is added, the pH of the crosslinking agent solution In the case of an extremely lowered and partially neutralized water-absorbing resin containing an acid group, the acidification of the surface occurs in particular, making it difficult to control the permeability of the crosslinking agent. Also, acidification of the surface is not preferable because it tends to increase the adhesion between the particles of the water-absorbent resin and lead to the formation of aggregates. As a result, there is a problem in that it is difficult to obtain a satisfactory performance because the desired cross-linking density of the surface layer of the water-absorbent resin particles cannot be obtained.
[0008]
The method (3) is based on a combination of an additive (base) and a compound (polyvalent metal salt, polyepoxy compound, polyaziridinyl compound, polyisocyanate compound) having two or more functional groups that easily react with a carboxyl group. Surface cross-linking is disclosed, gel strength and relatively low load (20 g / cm²) To improve the absorption capacity under pressure. However, the method of JP-A-6-298842 is still insufficient for improving the mixing property of the surface cross-linking agent and improving the physical properties of the water-absorbent resin. In particular, the SFC and the high load (4.83 kPa, Approx. 50 g / cm²), It was difficult to improve the absorption capacity under pressure (AAP) (both described later).
[0009]
Moreover, as a typical water-absorbing resin, acrylic acid-based water-absorbing resin comprising a partially neutralized salt of acrylic acid is cited from the viewpoint of its high physical properties and cost. The acrylic acid water-absorbing resin can be produced by a method of polymerizing acrylic acid and its salt previously neutralized to a predetermined neutralization rate (hereinafter referred to as neutralization polymerization method), non-neutralized to low Two methods (hereinafter referred to as an acid-type polymerization method) are generally performed in which neutralized acrylic acid is polymerized and then the polymer gel is post-neutralized.
Compared to the neutralization polymerization method, the latter acid type polymerization method tends to obtain a water-absorbent resin with a high absorption capacity and a low solubility, but uniformly neutralizes the hydrogel crosslinked polymer after polymerization. It takes a long time and is technically very difficult, and the neutralization rate of the individual particles of the resulting water-absorbent resin powder may be uneven. In such a case, although the water-absorbing resin of the acid type polymerization method has a high absorption ratio and a low solubility, it is not possible to obtain sufficient water-absorbing agent performance even if surface cross-linking treatment is performed. -10173 (European Patent Publication No. 0882502A1).
[0010]
In other words, conventionally, when surface cross-linking of a water-absorbing resin, the required surface cross-linking treatment differs depending on the difference in neutralization rate, and even with an optimal cross-linking treatment at a certain neutralization rate, the desired water absorption at other neutralization rates. When the performance of the water-absorbing agent is not obtained, or when the neutralization rates of the individual particles of the water-absorbent resin powder are mixed, the desired performance of the water-absorbing agent may not be obtained.
As described above, depending on the conventional technology, the surface cross-linking treatment cannot be performed uniformly, and as a result, various physical properties of the resulting water-absorbent resin (CRC, AAP, SFC, etc., which will be described later, particularly SFC) are obtained. As the balance deteriorated, the SFC was uneven. For this reason, for example, there has been a large difference in performance among the diaper performance lot fluctuation and even one diaper.
[0011]
[Problems to be solved by the invention]
  The present invention has been made in view of the above-described conventional problems. That is, an object of the present invention is to provide a water-absorbent resin that does not inhibit a crosslinking reaction while exhibiting an effect as a mixing aid, and also has an effect as a reaction catalyst in some cases and is partially neutralized and polymerized. It is an object of the present invention to provide a method for producing a water-absorbing agent capable of exhibiting uniform surface cross-linking regardless of the difference in the neutralization rate and the uniformity of the neutralization rate due to the post-neutralization operation after acid type polymerization. Furthermore, the problem of the present invention is excellent in the balance between absorption capacity under no pressure, absorption capacity under pressure, and saline flow inductivity, and the value of the saline flow inductivity in each lot during production or in each lot. To manufacture water-absorbing agent with small physical fluctuation and stable physical properties in a short timeThe lawThere is also to provide.
[0012]
[Means for Solving the Problems]
  As a result of intensive investigation of a water-absorbing agent having excellent absorption characteristics, the present inventor has found that the above-mentioned problems can be solved by using a specific additive together with a specific cross-linking agent of a water-absorbent resin, thereby completing the present invention. Reached.
[0016]
  That is, the method for producing a water absorbing agent according to the present invention is as follows.,
A method for producing a water-absorbing agent comprising mixing a water-absorbing resin powder (a) containing an acid group with a surface cross-linking agent (c) capable of reacting with the acid group, and crosslinking the water-absorbing resin powder (a).
  The water-absorbent resin powder has a weight average particle diameter (D50) based on the following definition of 300 to 600 μm and a fine powder having a weight of 150 μm or less of 10% by weight or less. The amount is 0.005-0.5 mol%) and when the surface cross-linking agent is mixed,Partial alkali metal salt of inorganic polybasic acid or partial alkali metal salt of organic polyvalent carboxylic acidNon-reducing alkali metal salt pH buffer (b2) is also mixed.
It is characterized by that.
  However, the weight average particle diameter (D50) of the water-absorbent resin powder is sieved with a JIS standard sieve (850 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, 75 μm), and the residual percentage R is logarithmic probability paper. It is specified by plotting.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail. Hereinafter, the water-absorbing agent in the present invention is a water-absorbing resin having a crosslinked structure (hereinafter simply referred to as a water-absorbing resin) as a main component (preferably 50 to 100% by weight, more preferably 80 to 100% by weight, More preferably, the water-absorbing resin is further modified (preferably surface-modified, particularly surface-crosslinked) with a crosslinking agent.
(Method for producing water-absorbing resin)
Hereinafter, in the present invention, the acid group-containing water-absorbent resin powder is referred to as a water-absorbent resin powder (a), and among these water-absorbent resin powders (a), those having further controlled particle size, for example, a weight average particle diameter of 300 A powder having a fine powder of ˜600 μm and 150 μm or less of 10% by weight or less is referred to as a water absorbent resin powder (a1).
[0019]
The water-absorbing resin of the present invention is a conventionally known water-absorbing resin. For example, in ion-exchanged water, a large amount of water of 5 times or more, preferably 50 to 1000 times its own weight is essential. It is a conventionally known crosslinked polymer that absorbs and forms an anionic, nonionic or cationic water-insoluble hydrogel.
These are generally particulate water-absorbing agents mainly composed of a water-absorbing resin having a crosslinked structure obtained by polymerizing an unsaturated monomer component (preferably an acid group, particularly a carboxyl group-containing unsaturated monomer). The polymer was polymerized in the state of a monomer solution, and the polymer was dried as necessary, and was usually pulverized before and / or after drying. Examples of such a water-absorbing resin include a polyacrylic acid partially neutralized polymer, a starch-acrylonitrile graft polymer hydrolyzate, a starch-acrylic acid graft polymer, and a saponified vinyl acetate-acrylic acid ester copolymer. , One or more of hydrolyzate of acrylonitrile copolymer or acrylamide copolymer, cross-linked product thereof, carboxyl group-containing cross-linked polyvinyl alcohol modified product, cross-linked isobutylene-maleic anhydride copolymer, etc. it can.
[0020]
These water-absorbing resins may be used singly or as a mixture. Among them, an acid group-containing water-absorbing resin, more preferably a carboxyl group-containing water-absorbing resin which is a carboxylic acid or a salt thereof, or a mixture thereof is preferable. A polymer obtained by polymerizing and cross-linking a monomer having acrylic acid and / or a salt thereof (neutralized product) as a main component, that is, a polyacrylate cross-linking containing a graft component if necessary A polymer is a main component.
The water-absorbing resin must be water-swellable and water-insoluble, and the uncrosslinked water-soluble component (water-soluble polymer) in the water-absorbing resin is preferably 50% by weight or less. It is preferably 25% by weight or less, more preferably 20% by weight or less, still more preferably 15% by weight or less, particularly preferably 10% by weight or less.
[0021]
Examples of the acrylate include alkali metal salts such as sodium, potassium and lithium of acrylic acid, ammonium salts and amine salts. The above water-absorbent resin preferably has a constitutional unit in the range of 0 to 50 mol% acrylic acid and 100 to 50 mol% acrylate (however, the total amount of both is 100 mol% or less). What is in the range of 10-40 mol% of acid and 90-60 mol% of acrylate (however, the total amount of both shall be 100 mol% or less) is more preferable. This molar ratio of acid to salt is called the neutralization rate. Neutralization of the water-absorbing resin for forming the salt may be performed in the monomer state before polymerization, or may be performed in the polymer state during or after the polymerization, or they may be used in combination. May be.
[0022]
Generally, when an unneutralized or low-neutralized monomer is polymerized and neutralized in the state of a polymer (acid type polymerization method), a water-absorbent resin having a high absorption ratio and a low solubility tends to be obtained. However, considerable effort, equipment and time are required for uniform neutralization of individual particles of the water-absorbent resin (Japanese Patent Laid-Open No. 10-10173). However, by using the method of the present invention, it is possible to satisfactorily use all the water-absorbing resins for surface cross-linking regardless of the neutralized state of the water-absorbing resin and the production method. Physical properties and productivity can be greatly improved.
The monomer for obtaining the water absorbent resin used in the present invention may contain a monomer other than the acrylic acid (salt) as required. Although it does not specifically limit as monomers other than acrylic acid (salt), Specifically, for example, methacrylic acid, maleic acid, vinyl sulfonic acid, styrene sulfonic acid, 2- (meth) acrylamide- Anionic unsaturated monomers such as 2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid and their salts; acrylamide, methacrylamide, N-ethyl (meth) Acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene Glycol (meth) acrylate, polyester Nonionic hydrophilic group-containing unsaturated monomers such as lenglycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine and N-vinylacetamide; N, N-dimethylamino Cations such as ethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and quaternary salts thereof Unsaturated unsaturated monomers. These monomers may be used alone or in combination of two or more as appropriate.
[0023]
In the present invention, when a monomer other than acrylic acid (salt) is used, the monomer other than acrylic acid (salt) is based on the total amount of acrylic acid and its salt used as a main component. The ratio is preferably 30 mol% or less, more preferably 10 mol% or less. By using a monomer other than the acrylic acid (salt) in the above proportion, the absorption characteristics of the finally obtained water-absorbing resin (water-absorbing agent) are further improved, and the water-absorbing resin (water-absorbing agent) is used. It can be obtained even more inexpensively.
When polymerizing the above-mentioned monomer to obtain the water-absorbent resin used in the present invention, bulk polymerization or precipitation polymerization can be performed. However, performance and ease of control of polymerization, and swelling gel From the viewpoint of the absorption characteristics, it is preferable to perform aqueous solution polymerization or reverse phase suspension polymerization by using the monomer as an aqueous solution. When the monomer is an aqueous solution, the concentration of the monomer in the aqueous solution (hereinafter referred to as the monomer aqueous solution) is determined by the temperature of the aqueous solution and the monomer, and is not particularly limited. Is preferably in the range of 10 to 70% by weight, and more preferably in the range of 20 to 60% by weight. Moreover, when performing the said aqueous solution polymerization, you may use together solvents other than water as needed, and the kind of solvent used together is not specifically limited.
[0024]
As a method of aqueous solution polymerization, a monomer aqueous solution is polymerized in a double-arm kneader while crushing the resulting hydrogel, or a monomer aqueous solution is supplied in a predetermined container or on a driving belt for polymerization. And a method of pulverizing the obtained gel with a meat chopper or the like.
When starting the polymerization, for example, potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) dihydrochloride, etc. A radical polymerization initiator or a photopolymerization initiator such as 2-hydroxy-2-methyl-1-phenyl-propan-1-one can be used.
[0025]
Further, a reducing agent that promotes the decomposition of the polymerization initiator can be used in combination, and a redox initiator can be obtained by combining the two. Examples of the reducing agent include (bi) sulfurous acid (salt) such as sodium sulfite and sodium bisulfite, L-ascorbic acid (salt), reducing metal (salt) such as ferrous salt, amines, and the like. Although it is mentioned, it is not particularly limited.
The amount of these polymerization initiators used is usually 0.001 to 2 mol%, preferably 0.01 to 0.1 mol%. When the amount of these polymerization initiators used is less than 0.001 mol%, the amount of unreacted monomers increases, and therefore the amount of residual monomers in the resulting water-absorbing resin and water-absorbing agent increases. It is not preferable. On the other hand, when the usage-amount of these polymerization initiators exceeds 2 mol%, since the amount of water-soluble components in the obtained water-absorbing resin or water-absorbing agent increases, it may not be preferable.
[0026]
Further, the polymerization reaction may be initiated by irradiating the reaction system with active energy rays such as radiation, electron beam, and ultraviolet rays, and the above polymerization initiator may be used in combination. The reaction temperature in the polymerization reaction is not particularly limited, but is preferably in the range of 15 to 130 ° C, and more preferably in the range of 20 to 120 ° C. Further, the reaction time and the polymerization pressure are not particularly limited, and may be appropriately set according to the type of monomer or polymerization initiator, the reaction temperature, and the like.
The water-absorbing resin may be of a self-crosslinking type that does not use a crosslinking agent, but is a crosslink having two or more polymerizable unsaturated groups or two or more reactive groups in one molecule. More preferably, a co-polymerized or reacted agent (internal cross-linking agent for water-absorbing resin) is used.
[0027]
Specific examples of these internal crosslinking agents include, for example, N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri ( (Meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, tri Allylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene Glycol, propylene glycol, glycerol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethylenimine, and glycidyl (meth) acrylate
These internal cross-linking agents may be used alone or in combination of two or more. These internal cross-linking agents may be added to the reaction system all at once or in divided portions. In the case of using at least one kind or two or more kinds of internal cross-linking agents, a compound having two or more polymerizable unsaturated groups in consideration of the absorption characteristics of the finally obtained water-absorbing resin or water-absorbing agent Is preferably used during the polymerization.
[0028]
The amount of these internal crosslinking agents to be used is preferably 0.001 to 2 mol%, more preferably 0.005 to 0.5 mol%, still more preferably 0.001 mol%, based on the above-mentioned monomers (excluding the crosslinking agent). The content is in the range of 01 to 0.2 mol%, particularly preferably 0.03 to 0.15 mol%. When the amount of the internal cross-linking agent used is less than 0.001 mol% and more than 2 mol%, sufficient absorption characteristics may not be obtained.
When a crosslinked structure is introduced into the polymer using the internal cross-linking agent, the internal cross-linking agent is added to the reaction system before, during or after the polymerization of the monomer, or after the polymerization or neutralization. What should I do?
[0029]
In the above polymerization, the reaction system includes starch / cellulose, starch / cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), polyacrylic acid (salt) cross-linked hydrophilic polymer 0 to 50% by weight. (To monomer) and other 0-10 wt% foaming agents such as carbonic acid (hydrogen) salts, carbon dioxide, azo compounds, inert organic solvents; various surfactants; chelating agents; hypophosphorous acid ( A chain transfer agent such as salt) may be added.
When the cross-linked polymer is obtained by aqueous solution polymerization and is in a gel form, that is, a hydrogel cross-linked polymer, the cross-linked polymer is dried as necessary, and before and / or after drying. Is usually pulverized to make a water-absorbent resin. Moreover, drying is normally performed in the temperature range of 60 to 250 degreeC, Preferably it is 100 to 220 degreeC, More preferably, it is 120 to 200 degreeC. The drying time depends on the surface area of the polymer, the moisture content, and the type of dryer, and is selected to achieve the desired moisture content.
[0030]
The water content of the water-absorbing resin or water-absorbing agent that can be used in the present invention (specified by the amount of water contained in the water-absorbing resin or water-absorbing agent / measured by loss on drying at 180 ° C. for 3 hours) is not particularly limited. In view of the physical properties of the water-absorbing agent, the powder exhibits fluidity at room temperature, more preferably 0.2 to 30% by weight, still more preferably 0.3 to 15% by weight, particularly preferably 0.5 to 10% by weight. It is a powder state.
Moreover, as a water absorbing resin which can be used for the manufacturing method of this invention, a powdered thing can be mentioned. The water-absorbent resin particles obtained by polymerization reaction may have a gel-like average particle size before drying and pulverization exceeding 1000 μm. However, since they are not normally powdered, they are preferably (preferably) dried and pulverized.・ By classifying, the particle size is adjusted according to the purpose.
[0031]
The particle diameter of the water-absorbent resin powder or the water-absorbing agent is a weight average particle diameter of 10 to 2000 μm, preferably 100 to 1000 μm, more preferably 200 to 700 μm, still more preferably 300 to 600 μm, and particularly preferably 400 to 550 μm. Are preferably used. More preferably, the water-absorbent resin powder or the fine powder in the water-absorbing agent (for example, 100 μm or less, preferably 150 μm or less) is preferred to be less, specifically 10% by weight or less, further 5% by weight or less, In particular, it is preferably 1% by weight or less. The water-absorbent resin powder and the water-absorbing agent are preferably substantially 1000 μm or more, more preferably 850 μm or more of particles in an amount of 5% by weight or less, further 1% by weight or less.
[0032]
The particle shape of the water-absorbing resin and water-absorbing agent thus obtained is not particularly limited, such as spherical, crushed, and irregular shapes, but is preferably an irregularly crushed one obtained through the pulverization step. Can be used. Further, the bulk specific gravity (specified in JIS K-3362) is preferably 0.40 to 0.80 g / ml, more preferably 0.50 to 0.75 g / ml, and still more preferably, due to the excellent physical properties of the water-absorbing agent. The range is 0.60 to 0.73 g / ml.
The water-absorbent resin obtained by the above method usually has a saturated absorption ratio with respect to physiological saline under no pressure, of about 10 to 100 g / g, and the physical properties such as the absorption ratio are appropriately adjusted according to the purpose. Is done.
[0033]
(Water-soluble inorganic base (b1))
In the present invention, the water-absorbent resin powder (a) or (a1) is non-crosslinkable water-soluble inorganic base (b1), that is, preferably an alkali metal salt, an ammonium salt, an alkali metal hydroxide, and , Ammonia or a hydroxide thereof, a water-soluble inorganic base (b1) (hereinafter referred to as a water-soluble inorganic base (b1)), and / or a non-reducing alkali metal salt pH buffer (b2) ) And a crosslinking agent (c) or a dehydration-reactive crosslinking agent (c1) are added. Hereinafter, the water-soluble inorganic base (b1) will be described.
[0034]
That is, in the present invention, the water-soluble inorganic base is dissociated in an aqueous solution, so that water or OH^-Inorganic compounds (including carbonates and bicarbonates) that generate salts by neutralizing acid groups. The water-soluble inorganic base (b1) used in the present invention is preferably selected from the group consisting of alkali metal salts, ammonium salts, alkali metal hydroxides, and ammonia or hydroxides thereof. It is a substantially non-crosslinkable water-soluble inorganic base. (Note that examples of the water-soluble inorganic base that is crosslinkable with respect to the acid group-containing water-absorbing resin include polyhydric metal hydroxides typified by calcium hydroxide and aluminum hydroxide. Valence metals are not included in the water-soluble inorganic bases of the present invention).
[0035]
As the water-soluble inorganic base (b1), it is essential that it is water-soluble in view of the properties of the resulting water-absorbing agent, and is usually 5 g or more, preferably 20 g or more, more preferably 50 g or more, more preferably 100 g of room temperature water. Those having a solubility of 100 g or more are used. In the present invention, the combined use of a water-insoluble inorganic base, an organic base or a crosslinkable inorganic base (polyhydric metal hydroxide) is not excluded, but a non-crosslinkable water-soluble inorganic base (b1) is not used. The physical properties of the obtained water-absorbing agent are low.
Specifically, as the water-soluble inorganic base (b1), a carbonate compound containing an alkali metal salt such as lithium carbonate, sodium carbonate, potassium carbonate, sodium carbonate, cesium carbonate, rubidium carbonate, ammonium carbonate, and / or ammonium salt, and its Hydrates (decahydrate, heptahydrate, 1.pentahydrate, monohydrate, etc.), lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, cesium bicarbonate, rubidium bicarbonate, ammonium bicarbonate, etc. Bicarbonate containing metal and / or ammonium, lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, rubidium hydroxide, ammonium hydroxide, hydroxide compounds containing ammonium such as water glass, phosphoric acid Disodium hydrogen, dipotassium hydrogen phosphate, dilithium hydrogen phosphate, hydrogen phosphate Rubidium, hydrogen phosphate compound, such as hydrogen phosphate 2 cesium, sodium sesquicarbonate (Na₂CO_Three・ NaHCO_Three・ 2H₂Complex salts such as O) may be mentioned, and two or more of these may be mixed or used together. These water-soluble inorganic bases (b1) are purchased, stored or used as powders, hydrates thereof, pellets or aqueous solutions, but the form is not limited.
[0036]
Among the water-soluble inorganic bases (b1), an alkali metal salt, preferably a lithium salt, a sodium salt or a potassium salt, more preferably a sodium salt is used from the viewpoint of physical properties and solubility. Among the compounds (b1), from the viewpoint of physical properties, carbonate / bicarbonate / hydroxide is preferred, more preferably hydroxide and / or bicarbonate, particularly preferably hydroxide. That is, specifically, as the water-soluble inorganic base (b1), preferably sodium bicarbonate and / or sodium hydroxide, more preferably sodium hydroxide is used.
The amount of the water-soluble inorganic base (b1) used in the present invention is 0.001 to 10 parts per 100 parts by weight of the water-absorbent resin when not used in combination with the non-reducing alkali metal salt pH buffer (b2) described later. It is preferably in the range of parts by weight, more preferably in the range of 0.01 to 5 parts by weight, and still more preferably in the range of 0.01 to 2 parts by weight. By using it within the above range, the absorption characteristics for body fluids (aqueous liquids) such as urine, sweat and menstrual blood can be further improved. When the amount used is less than 0.001 part by weight, the neutralization rate of the functional group in the vicinity of the surface of the water-absorbent resin cannot be appropriately adjusted, and the absorption characteristics may not be improved. When the amount of the water-soluble inorganic base (b1) used is more than 10 parts by weight, the amount becomes excessive, which is uneconomical and the absorption capacity may not be improved.
[0037]
In the case where the water-soluble inorganic base (b1) is used in combination with the non-reducing alkali metal salt pH buffer (b2) described later, for the same reason as described above, the total use amount thereof is the water-absorbing resin 100. It is preferably in the range of 0.001 to 10 parts by weight, more preferably in the range of 0.01 to 5 parts by weight, and still more preferably in the range of 0.01 to 2 parts by weight with respect to parts by weight. However, in the present invention, when the water-soluble inorganic base (b1) and the non-reducing alkali metal salt pH buffer (b2) described later are used in combination, (b1) and (b2) within the range showing at least one of the functions. Are used together as appropriate.
Although the mechanism for improving the absorption characteristics is not clear, the following two reasons ((1) formation of a uniform surface cross-linking layer by uniformizing the surface neutralization rate, (2) optimization of mixing and penetration by changing the salt concentration) )It is estimated to be.
[0038]
That is, as the reason (1), in the water-absorbent resin powder, the water-absorbent resin powder is generally contained in each particle regardless of the post-neutralization after the polymerization (the neutralization polymerization method or the acid type polymerization method described above). The neutralization rate of the powder surface differs slightly even with the same rate or even the same single powder. In conventional surface treatment, the powder cross-linking reaction and mixing of the cross-linking agent are not uniform due to these reasons. As a result, the physical properties deteriorated. Therefore, in the present invention, by using the water-soluble inorganic base (b1) together with the crosslinking agent (c), the neutralization rate of each particle of the water-absorbent resin powder and the minute surface neutralization of the powder By eliminating the difference in rate, the neutralization rate of the carboxyl groups in the vicinity of the surface involved in crosslinking can be optimized uniformly, and as a result, surface crosslinking can be performed uniformly. For example, the water-absorbing agent obtained from 70 mol% neutralized polyacrylic acid-based water-absorbing resin and 0.01 to 2 parts by weight of sodium hydroxide is in the range of 0.025 to 5 mol%. And is selectively highly neutralized near the surface of the particles. Furthermore, it is presumed that the water-soluble inorganic base (b1) of the present invention also acts as a reaction catalyst for the crosslinking agent due to improved absorption characteristics.
[0039]
In addition, as the reason (2), the water-soluble inorganic base (b1) is derived from a high salt concentration in the crosslinking agent solution at the time of mixing the crosslinking agent, thereby controlling the penetration into the water-absorbent resin and improving the mixing property. After mixing, it neutralizes with the carboxyl group of the water-absorbent resin and becomes an alkali metal salt and ammonium salt, which disappears from the crosslinking agent solution. Therefore, it is estimated that it works to promote penetration of the crosslinking agent. . This is because conventional additives (hydrophilic organic solvents such as isopropanol) control the penetration of the water-absorbing resin derived from the inert organic solvent and improve the mixing, but the organic solvent remains the crosslinker solution after mixing. It is presumed that it remains inside and prevents the cross-linking agent from penetrating into the surface.
[0040]
In addition, unlike a water-soluble inorganic base (b1), when a polyvalent metal salt such as aluminum is used, the cross-linking reaction proceeds with a polyvalent metal ion, reducing the absorption capacity under no pressure or under pressure. I guess it is. Furthermore, cross-linking with polyvalent metal ions is very weak because it forms ionic bonds, and in the water-swollen state, polyvalent metal ions move into the particles and form cross-links, resulting in further deterioration in physical properties. Guessed.
It is presumed that the water-soluble inorganic base (b1) of the present application has improved the conventional disadvantage that the thickness of the crosslinked layer of the water-absorbing agent resulting from the above phenomenon is insufficient and the physical properties are lowered. Furthermore, by using the dehydration-reactive crosslinking agent (c1), it is estimated that the cross-linking agent further penetrates into the vicinity of the surface due to water generated from the dehydration crosslinking reaction, and the thickness of the crosslinked layer is further increased.
[0041]
(Non-reducing alkali metal salt pH buffer (b2))
In the present invention, the non-crosslinkable water-soluble inorganic base (b1), that is, alkali metal salt, ammonium salt, alkali metal hydroxide, and ammonia or the water-absorbent resin powder (a) or (a1) Water-soluble inorganic base (b1) selected from the group consisting of hydroxides and the like, and / or non-reducing alkali metal salt pH buffer (b2), and crosslinking agent (c) or dehydration-reactive crosslinking agent ( Although c1) is added, the non-reducing alkali metal salt pH buffer (b2) will be described below.
[0042]
The non-reducing alkali metal salt pH buffer (b2) in the present invention maintains a substantially constant hydrogen ion concentration even in the absence of a certain amount of acid or base addition in the solution, and is essentially non-reducing. Preferably, a non-oxidizing alkali metal salt is used (for example, in the case of an alkali metal salt pH buffer containing phosphorus or sulfur, if the oxidation number of phosphorus atoms is + 5 / the oxidation number of sulfur atoms is +6, pH buffer exhibits non-oxidizing and non-reducing properties).
If the pH buffering agent has reducibility or is not an alkali metal salt, crosslinking may be inhibited, and the object of the present invention cannot be sufficiently achieved. The present invention is applied to pH buffer agents that are alkali metal salts that act as pH buffer agents and are made from various acid, base, or salt combinations. Moreover, the molecular weight of a pH buffer agent is 50-1000, Furthermore, the thing of 60-800, especially 70-500 is used from the mixing property to a water absorbing resin, or permeability.
[0043]
Examples of the alkali metal salt that functions as the pH buffer (b2) in the present invention typically include one or more of hydrogen carbonate, dihydrogen phosphate, and hydrogen phosphate.
Specific examples include partial alkalis of inorganic polybasic acids such as sodium hydrogen carbonate, potassium hydrogen carbonate, lithium hydrogen carbonate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate. Metal salts: Organic polyvalent carboxylic acids such as potassium dihydrogen citrate, sodium dihydrogen citrate, disodium hydrogen citrate, dipotassium hydrogen citrate, sodium hydrogen tartrate, potassium hydrogen tartrate, monosodium fumarate, potassium hydrogen phthalate And partial alkali metal salts, especially sodium salts or potassium salts, and lithium salts.
[0044]
In addition to the pH buffering agent (b2), the pH buffering agent (b2) prepared from a combination of various acids, bases or salts referred to in the present invention is typically a conventionally known buffer solution. Examples are buffers made from the combination of compounds used in making. The buffer solution is an aqueous solution of a buffer solution, particularly a salt composed of a weak acid and a strong base, a salt composed of a strong acid and a weak base, or a mixture of these salts. In the case of a water-absorbing resin containing an acid group such as a carboxyl group, a buffer as a mixture of salts consisting of a weak acid and a strong base is preferably used, and more preferably an inorganic salt is used.
[0045]
As a specific example, a combination of compounds used in the buffer described in Chemical Handbook (edited by the Chemical Society of Japan, II-355, 356) can be mentioned as a buffer. For example, Clark-Lubs buffer (potassium chloride / hydrochloric acid; pH 1.0 to 2.2, potassium hydrogen phthalate / hydrochloric acid; pH 2.2 to 3.8, potassium hydrogen phthalate / sodium hydroxide; pH 4.0 to 6.2, potassium dihydrogen phosphate / sodium hydroxide; pH 5.8-8.0, boric acid / potassium chloride / sodium hydroxide; pH 7.8-10.0), Sφrensen's buffer (glycine + sodium chloride) PH 1.1-4.6, glycine + sodium chloride / hydrochloric acid; pH 8.6-13.0, sodium citrate / hydrochloric acid; pH 1.1-4.9, sodium citrate / sodium hydroxide; pH 5. 0 to 6.7, sodium tetraborate / hydrochloric acid; pH 7.6 to 9.2, sodium tetraborate / sodium hydroxide; pH 9.3 to 12.4, dihydrogen phosphate potassium Um / disodium hydrogen phosphate; pH 5.3-8.0), Kolthoff's buffer (potassium citrate / citric acid; pH 2.2-3.6, potassium dihydrogen citrate / hydrochloric acid; pH 2.2-3 .6, potassium dihydrogen citrate / sodium hydroxide; pH 3.8-6.0, succinic acid / sodium tetraborate; pH 3.0-5.8, potassium dihydrogen citrate / sodium tetraborate; pH 3. 8 to 6.0, potassium dihydrogen phosphate / sodium tetraborate; pH 5.8 to 9.2, sodium tetraborate / sodium carbonate; pH 9.2 to 11.0, hydrochloric acid / sodium carbonate; pH 10.2 to 11.2, disodium hydrogen phosphate / sodium hydroxide; pH 11.0-12.0), Michaelis buffer (tartaric acid / sodium tartrate; pH 1.4-4.5, lactic acid / Sodium lactate; pH 2.3 to 5.3, acetic acid / sodium acetate; pH 3.2 to 6.2, potassium dihydrogen phosphate / disodium hydrogen phosphate; pH 5.2 to 8.3, sodium diethyl barbiturate + Sodium acetate / hydrochloric acid; pH 2.6-9.2, sodium diethylbarbiturate / hydrochloric acid; pH 6.8-9.6, N, N-dimethylglycine sodium salt / hydrochloric acid; pH 8.6-10.6), Mcilvaine Wide-area buffer (disodium hydrogen phosphate / citric acid; pH 2.2-8.0), Britton-Robinson's wide-area buffer (citric acid + potassium dihydrogen phosphate + boric acid + diethyl barbituric acid / phosphoric acid Trisodium), Carmody's broad buffer (boric acid + citric acid / trisodium phosphate; pH 2.0-12.0), Gomori's Impulse liquid (2,4,6-trimethylpyridine / hydrochloric acid; pH 6.4 to 8.4, tris (hydroxymethyl) aminomethane / hydrochloric acid; pH 7.2 to 9.1,2-amino-2-methyl-1,3 -Propanediol / hydrochloric acid; pH 7.8-9.7), Bates-Bower Tris buffer (Tris (hydroxymethyl) aminomethane / hydrochloric acid; pH 7.0-9.0), Delhi-King buffer (carbonate) / Bicarbonate; pH 9.2 to 10.7). The pH and concentration of the buffer used depend on the neutralization rate of the water-absorbent resin and the type of surface cross-linking agent used, but preferably the pH of the surface cross-linking agent solution is 1 by adding a buffer. It is adjusted in the range of .5 to 10.0.
[0046]
Among these, partially neutralized salts of inorganic polybasic acids are preferable from the viewpoint of performance, stability, use in a one-component system, cost, and the like, and partially alkali metal neutralized salts of phosphoric acid and carbonic acid are more preferable.
The amount of the pH buffer (b2) used in the present invention is 0.005 to 10 parts by weight with respect to 100 parts by weight of the solid content of the water-absorbent resin when not used in combination with the water-soluble inorganic base (b1). Is preferable, and the range of 0.05 to 5 parts by weight is more preferable. By using it within the above range, the absorption characteristics for body fluids (aqueous liquids) such as urine, sweat and menstrual blood can be further improved. If the amount used is less than 0.005 parts by weight, the neutralization rate of the functional group in the vicinity of the surface of the water-absorbent resin cannot be appropriately adjusted, and the absorption characteristics may not be improved. When the amount of the pH buffer (b2) used is more than 10 parts by weight, the additive becomes excessive, which is uneconomical and may not improve the absorption capacity.
[0047]
In the case where the non-reducing alkali metal salt pH buffer (b2) is used in combination with the water-soluble inorganic base (b1), the total amount of the non-reducing alkali metal salt pH buffer (b2) is 100% for the same reason as described above. It is preferably in the range of 0.001 to 10 parts by weight, more preferably in the range of 0.01 to 5 parts by weight, and still more preferably in the range of 0.01 to 2 parts by weight with respect to parts by weight. However, in the present invention, when the water-soluble inorganic base (b1) and the non-reducing alkali metal salt pH buffer (b2) are used in combination, (b1) and (b2) are within a range showing at least one of the functions. Used in combination as appropriate.
Although the mechanism for improving the absorption characteristics is not clear, it is presumed for the following two reasons ((1) uniform surface neutralization rate and (2) optimization of mixing and penetration by changing the salt concentration).
[0048]
That is, as the reason (1), in the water-absorbent resin powder, neutralization of each particle of the water-absorbent resin powder irrespective of the presence or absence of post-neutralization after polymerization (the above-described neutralization polymerization method or acid type polymerization method). Even if the powder is the same grain, the neutralization rate on the surface of the powder is slightly different, and the physical properties have been lowered due to nonuniformity in the cross-linking reaction of the powder and the mixing of the cross-linking agent. By using the pH buffering agent (a) of the present invention in combination with the crosslinking agent (b), the difference in the neutralization rate of each particle of the water-absorbent resin powder and the minute surface neutralization rate of the powder of one particle Therefore, regardless of the neutralization rate of the water-absorbent resin powder and the neutralization index described later, in the present invention, the neutralization rate of the carboxyl groups in the vicinity of the surface involved in crosslinking can be uniformly optimized. This is probably because of this. As a result, the pH buffering agent of the present invention acts as a mixing aid without interfering with the penetration of the crosslinking agent into the water-absorbent resin powder, and further acts as a reaction catalyst for the crosslinking agent. It is presumed that this is due to improved characteristics.
[0049]
In addition, as a reason (2), since a pH buffer such as hydrogen carbonate exists as an alkali metal salt in the cross-linking agent solution when the cross-linking agent is mixed, it controls the penetration of the water-absorbing resin derived from a high salt concentration. Although the mixing property has been improved, after mixing, the alkali metal salt of the pH buffering agent disappears from the crosslinking agent solution by neutralizing reaction with the carboxyl group of the water-absorbent resin, thus inhibiting the penetration of the crosslinking agent after mixing. It is presumed that the dissolved salt disappears and promotes the penetration of the crosslinking agent. This is because conventional additives (hydrophilic organic solvents such as isopropanol) control the penetration of the water-absorbing resin derived from the inert organic solvent and improve the mixing, but the organic solvent remains the crosslinker solution after mixing. It is presumed that the pH buffer of the present application has improved the conventional defect that remains in the inside and prevents the cross-linking agent from penetrating into the surface and the cross-linking layer of the water-absorbing agent is insufficient.
[0050]
(Crosslinking agent (c) and its mixture and crosslinking treatment)
In the present invention, as the crosslinking agent (c) capable of reacting with an acid group, a surface crosslinking agent, and further a dehydration reactive crosslinking agent (c1) are preferably used. In the present invention, the dehydration reactivity means that the functional group of the water-absorbent resin (particularly the functional group in the vicinity of the surface) and the crosslinking agent undergo a dehydration reaction, preferably dehydration esterification and / or dehydration amidation, more preferably It is a crosslinking agent that crosslinks by dehydration esterification.
Specifically, when the water-absorbing resin contains a carboxyl group, a hydroxyl group-containing cross-linking agent such as a polyhydric alcohol, an amino group-containing cross-linking agent such as a polyhydric amine, an alkylene carbonate, mono-, di- or poly- An oxazolidinone compound; a cyclic cross-linking agent such as an oxetane compound such as 3-methyl-3-oxetanemethanol, which generates a hydroxyl group or an amino group in accordance with a ring-opening reaction of the cyclic cross-linking agent, and the hydroxyl group or amino group Examples of the crosslinking agent (c1) that exhibits a dehydration reactivity include a cyclic crosslinking agent that performs a crosslinking reaction. One or more of the dehydration-reactive crosslinking agents (c1) are used, but a non-dehydration-reactive crosslinking agent such as a polyvalent metal may be used in combination.
[0051]
Specifically, as the dehydration-reactive cross-linking agent (c1) that can be used in the present invention, any cross-linking agent that can react with the functional group of the water-absorbent resin is used without limitation, and is usually used for the application. It is a crosslinking agent (surface crosslinking agent). For example, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, Glycerin, diglycerin, polyglycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2 -Multivalent alcohols such as cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethyleneoxypropylene block copolymer, pentaerythritol, sorbitol, etc. Polyamine compounds such as ethylenediamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyamide polyamine, polyallylamine, polyethyleneimine, and condensates of these polyamines and haloepoxy compounds; 3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolane- 2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,3 -Dioxane-2-one, 4,6-dimethyl-1,3-dioxan-2-one, 1,3-dioxopan-2-one An alkylene carbonate compound such as ethylene glycol bis (4-methylene-1,3-dioxolan-2-one) ether; a mono-, di- or polyoxazolidinone compound; 3-methyl-3- One or two or more types selected from oxetane compounds such as oxetane methanol and polyvalent oxetane compounds;
[0052]
Among these dehydration-reactive crosslinking agents, one or more selected from polyhydric alcohols, alkylene carbonates, oxazolidinone compounds, and (polyhydric) oxetane compounds are preferable, and at least polyhydric alcohols are particularly preferably used.
As the crosslinking agent (c), in addition to the dehydration-reactive crosslinking agent (c1), ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl Epoxy compounds such as ether, polyethylene diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycidol, and γ-glycidoxypropyltrimethoxysilane; polyvalent compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate Isocyanate compounds; polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; γ-glycidoxypropyltrimethoxysilane, γ- Silane coupling agents such as minopropyltrimethoxysilane; polyvalent aziridine compounds such as 2,2-bishydroxymethylbutanol-tris [3- (1-aziridinyl) propionate], beryllium, magnesium, calcium, strontium, zinc, aluminum And multivalent metals such as iron, chromium, manganese, titanium, and zirconium.
[0053]
In the present invention, the dehydration-reactive crosslinking agent (c1), the water-absorbent resin powder (a1) in which the fine powder having a weight average particle diameter of 300 to 600 μm and 150 μm or less is 10% by weight and / or the particle diameter is less than 850 μm. 150% or more of particles of 150 μm or more are contained, and the particle diameter is less than 850 μm and 600 μm or more (A1), the particle diameter is less than 600 μm and 500 μm or more (A2), the particle diameter is less than 500 μm When both the water absorbent resin powder containing at least two kinds selected from particles (A3) having a particle diameter of less than 300 μm and particles having a particle diameter of less than 300 μm (A4) are not used, the physical properties of the water absorbent generally obtained are low. Preferably, both the dehydration-reactive crosslinking agent (c1) and the water absorbent resin powder (a1) having the specific particle size are used in the present invention.
[0054]
In the present invention, the water-absorbent resin powder (a) or (a1), the water-soluble inorganic base (b1) and / or the non-reducing alkali metal salt pH buffer (b2), and the crosslinking agent (c) or (c1) ) Is preferably mixed with water. In this case, the amount of water used is usually 0.5 to 20 parts by weight, preferably 0.5 to 10 parts by weight based on 100 parts by weight of the water absorbent resin, although it depends on the water content of the water absorbent resin to be used. The range is parts by weight. If the amount of water used exceeds 20 parts by weight, the absorption capacity may decrease. If the amount is less than 0.5 parts by weight, the effect is difficult to appear, and the absorption capacity under pressure may not be improved.
[0055]
In the present invention, the water absorbent resin powder (a) or (a1), the water-soluble inorganic base (b1) and / or the non-reducing alkali metal salt pH buffer (b2), and the crosslinking agent (c) or When mixing (c1), a hydrophilic organic solvent may be used. Examples of the hydrophilic organic solvent used include alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, and t-butyl alcohol; ketones such as acetone and methyl ethyl ketone; dioxane, alkoxy (poly) ethylene Ethers such as glycol and tetrahydrofuran; amides such as ε-caprolactam and N, N-dimethylformamide; sulfoxides such as dimethyl sulfoxide; ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, polyp Pyrene glycol, glycerin, polyglycerin, glycerophosphoric acid, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1 , 2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymers, polyhydric alcohols such as pentaerythritol, sorbitol, etc. It is done.
[0056]
The amount of the hydrophilic organic solvent to be used varies depending on the type and particle size of the water-absorbent resin, but is usually 0 to 10 parts by weight, preferably 0 to 5 parts by weight, more preferably 0 to 100 parts by weight of the water-absorbent resin. It is in the range of ˜3 parts by weight. When the usage-amount of a hydrophilic organic solvent is 10 weight part or more, there exists a possibility that the solubility of the said additive may fall and an absorption characteristic may not improve. The polyhydric alcohol may be reacted with the water-absorbent resin depending on the reaction conditions (heating temperature, time, moisture content, etc.), may be used as a crosslinking agent, or may be used as a solvent without being reacted, or the functions thereof may be used in combination. May be.
Furthermore, in the present invention, the water-absorbent resin powder (a) or (a1), the additive (b1) and / or the non-reducing alkali metal salt pH buffer (b2), and the crosslinking agent (c) or (c1) ) May be used as a substance other than water or a hydrophilic organic solvent as long as it does not interfere with the effects of the present invention. Surfactants and inert inorganic fine particle powders used are exemplified in US Pat. No. 5,164,459, European Patent No. 827753, European Patent No. 349240, European Patent No. 761241 and the like.
[0057]
In the present invention, the water absorbent resin powder (a) or (a1), the water-soluble inorganic base (b1) and / or the non-reducing alkali metal salt pH buffer (b2), and the crosslinking agent (c) or ( The mixing of c1) may be performed in a state where the water-absorbing resin is dispersed in a hydrophilic organic solvent or an organic solvent such as cyclohexane or pentane, but the mixture of water, crosslinking agent and additive is divided into several times. The mixing method is not particularly limited. In addition, the water-soluble inorganic base (b1) and / or the non-reducing alkali metal salt pH buffer (b2) and the crosslinking agent (c) or (c1), water or hydrophilic organic used as necessary The solvent, inorganic powder, etc. may be mixed separately with respect to the water-absorbent resin, may be mixed in a lump, or may be mixed in several times, preferably a water-soluble inorganic base. (B1) and / or a non-reducing alkali metal salt pH buffer (b2) and a crosslinking agent (c) or (c1) are mixed in advance and then added to the water-absorbent resin. More preferably, b1) and / or the non-reducing alkali metal salt pH buffering agent (b2) and the crosslinking agent (c) or (c1) are made into an aqueous solution. Moreover, the temperature of the aqueous solution at this time is set to 0 ° C. to boiling point, preferably 5 to 50 ° C., and more preferably 10 to 30 ° C. in view of mixing property and stability. In addition, the temperature of the water absorbent resin powder (a) or (a1) before mixing is preferably in the range of 0 to 80 ° C., more preferably 40 to 70 ° C., from the viewpoint of mixing properties.
[0058]
Furthermore, in the present invention, water and / or a hydrophilic organic solvent, a water-soluble inorganic base (b1) and / or a non-reducing alkali metal salt pH buffer (b2), if necessary, among various mixing methods, and After the crosslinking agent (c) or (c1) is preliminarily mixed, a method of spraying or dropping and mixing the aqueous solution onto the water absorbent resin powder (a) is preferable, and a method of spraying is more preferable. The size of the droplets to be sprayed is preferably 300 μm or less, and more preferably 200 μm or less. In mixing, a water-insoluble fine particle powder and a surfactant may be allowed to coexist within a range not impeding the effects of the present invention.
[0059]
A suitable mixing device used for the mixing needs to be able to generate a large mixing force to ensure uniform mixing. Examples of the mixing apparatus that can be used in the present invention include a cylindrical mixer, a double wall conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, and a fluidizer. A mold furnace rotary disk type mixer, an airflow type mixer, a double arm type kneader, an internal mixer, a pulverizing type kneader, a rotary mixer, a screw type extruder and the like are suitable.
The method for producing a water-absorbing agent of the present invention comprises a water-absorbing resin powder (a) or (a1), a water-soluble inorganic base (b1) and / or a non-reducing alkali metal salt pH buffer (b2), and a crosslinking agent. (C) or (c1) is mixed, and the water-absorbent resin powder (a) or (a1) is subjected to a crosslinking treatment.
[0060]
In the method for producing a water-absorbing agent of the present invention, preferably, the water-absorbing resin powder (a) or (a1) is added with a water-soluble inorganic base (b1) and / or a non-reducing alkali metal salt pH buffer (b2), Then, after the crosslinking agent (c) or (c1) is mixed, a heat treatment is performed when the vicinity of the surface of the water absorbent resin is crosslinked.
When performing heat processing by this invention, 1 minute-180 minutes are preferable, 3 minutes-120 minutes are more preferable, and 5 minutes-100 minutes are further more preferable. The heat treatment temperature (specified by heat medium temperature or material temperature) is preferably in the range of 100 to 250 ° C, more preferably in the range of 140 to 240 ° C, further preferably in the range of 150 to 230 ° C, and in the range of 160 to 220 ° C. Even more preferred. When the heating temperature is less than 100 ° C., the heat treatment and dehydration reaction take time, not only causing a decrease in productivity, but also a uniform crosslinking is not achieved, and an excellent water absorbing agent may not be obtained. On the other hand, if the treatment temperature exceeds 250 ° C., the resulting water-absorbing agent may be damaged and it may be difficult to obtain a product having excellent physical properties.
[0061]
The heat treatment can be performed using a normal dryer or a heating furnace, and examples thereof include a groove type mixing dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, an airflow dryer, and an infrared dryer. .
In the method for producing a water-absorbing agent according to the present invention, further, if necessary, deodorant, antibacterial agent, fragrance, inorganic powder such as silicon dioxide and titanium oxide, foaming agent, pigment, dye, hydrophilic short Fibers, plasticizers, adhesives, surfactants, fertilizers, oxidizing agents, reducing agents, water, salts, chelating agents, fungicides, hydrophilic polymers such as polyethylene glycol and polyethyleneimine, hydrophobic polymers such as paraffin, A step of imparting various functions to the water-absorbing agent or the water-absorbing resin, such as adding a thermoplastic resin such as polyethylene or polypropylene, or a thermosetting resin such as polyester resin or urea resin, may be included. The amount of these additives used is 0 to 10 parts by weight, preferably 0 to 1 part by weight, based on 100 parts by weight of the water-absorbing agent.
[0062]
The cationic polymer compound used for the water-absorbing agent in the present invention can improve the fixability of the water-absorbing agent to a sanitary material, and preferably has a weight average molecular weight of 2000 or more, more preferably 5000 or more, and most preferably a weight average. The molecular weight is 10,000 or more. Moreover, the usage-amount becomes like this. Preferably it is 0.01-10 weight part with respect to 100 weight part of water absorbing resin, More preferably, it is 0.05-5 weight part, More preferably, it is 0.1-3 weight part. Mixing of the cationic polymer compound is added alone or in solution (aqueous solution), preferably after surface crosslinking. Specific examples of the cationic polymer compound include polyethyleneimine, polyvinylamine, polyallylamine, polyamidoamine and epichlorohydrin condensate, polyamidine, partial hydrolyzate of poly (N-vinylformaldehyde), and salts thereof. The
[0063]
The water-insoluble fine particles can be used to further improve the liquid permeability of the water-absorbing agent and the blocking resistance during moisture absorption. The fine particles used are preferably inorganic or organic water-insoluble fine particles of 10 μm or less, more preferably 1 μm or less, particularly 0.1 μm or less. Specifically, silicon oxide (trade name, Aerosil, manufactured by Aerosil Japan) , Titanium oxide, aluminum oxide, etc. are used. For mixing, powder mixing (Dry-Blend) or slurry mixing is used. The amount used is 10 parts by weight or less, more preferably 0.001 to 5 parts by weight, preferably 0.01. ~ 2 parts by weight are used.
[0064]
(Water-absorbing agent and sanitary material using it)
In the present invention, preferably, the water-absorbent resin powder (a) or (a1) is added to the water-soluble inorganic base (b1) and / or the non-reducing alkali metal salt pH buffer (b2), and the crosslinking agent (c ) Or (c1) is mixed, and the water-absorbent resin powder (a) or (a1) is crosslinked to provide a novel water-absorbing agent having high physical properties resulting from the effects of the present invention described above.
The water-absorbing agent according to the present invention is preferably a particulate water-absorbing agent mainly composed of a water-absorbing resin having a crosslinked structure obtained by polymerizing an unsaturated monomer component.
[0065]
(1) In the case of acid polymerization, the resulting water-absorbing agent
In the case of obtaining a water-absorbing resin by acid polymerization, the water-absorbing agent according to the present invention is preferably obtained by polymerizing a monomer containing an acid group-containing monomer (salt) and further post-neutralizing. It is a water-absorbing agent obtained by surface-crosslinking a resin. More preferably, the water-absorbent resin obtained by the post-neutralization has a neutralization index of 15 or more, more preferably 17 or more, and particularly preferably 20 or more. Preferably, the surface-crosslinked water-absorbing agent has a neutralization index of 15 or more, more preferably 17 or more, and particularly preferably 20 or more. When the neutralization index is lowered in order to enhance the surface crosslinking effect, the neutralization requires a long time and a complicated process, but in the present invention, excellent surface crosslinking can be easily achieved even with non-uniform neutralization.
[0066]
Conventionally, a water-absorbing resin obtained by polymerizing a monomer containing an acid group-containing monomer (salt) and further post-neutralizing has a high absorption capacity and low solubility. Since the sum is not uniform, the absorption capacity under pressure is generally difficult to improve. In order to solve this problem, Japanese Patent Laid-Open No. 10-101735 (European Patent Publication No. 0882502) discloses a technique for highly controlling the difference (neutralization index) in the neutralization rate of each particle of the water absorbent resin. It has been.
In such a method for controlling the neutralization index, a water-absorbing resin having a low solubility obtained by polymerizing a monomer containing an acid group-containing monomer (salt) and further neutralizing it, Although high absorption capacity under pressure was achieved, control of the neutralization index was very laborious. However, the method of the present invention using the alkali metal pH buffer (b2) of the present invention does not require a high degree of control of the neutralization index, and provides a high absorption capacity under pressure even with simple non-uniform post-neutralization. Highly preferred. Of course, the present invention is limited to the low water-soluble water-absorbing resin obtained by polymerizing a monomer containing an acid group-containing monomer (salt) and then neutralizing it after the acid-type polymerization method. However, as shown in the examples and the like described later, the present invention is also suitably applied to a water-absorbing resin by a neutralization polymerization method that does not include a post-neutralization step.
[0067]
(2) Novel water-absorbing agent that has five physical properties
In addition, including the case where acid polymerization is not performed, the water-absorbing agent of the present invention preferably has the following physical properties. In particular, in the present invention, in addition to the following five physical properties (particle size, CRC, AAP, SFC) 1 or more, preferably 2 or more, more preferably 3 or more, particularly preferably 4 or more) such as SFC change index, SFC variation coefficient, SFC variation rate, continuous production system SFC standard deviation, surface soluble component, etc. A new water-absorbing agent is also provided.
(A) Particle size
The average particle diameter and bulk specific gravity of the water-absorbing agent according to the present invention are preferably in the range of the water-absorbent resin, that is, the fine powder having a weight average particle diameter of 300 to 600 μm and 150 μm or less is 10% by weight or less. More preferably, it is 5% by weight or less, further preferably 3% by weight or less, particularly 2% by weight or less.
[0068]
The water-absorbing agent according to the present invention comprises particles having a particle size of less than 850 μm and 150 μm or more of 90% by weight or more of all particles, and a particle size of less than 850 μm and 600 μm or more (A1), wherein the particle size is less than 600 μm. Including at least two kinds selected from particles (A2) having a particle diameter of 500 μm or more, particles (A3) having a particle diameter of less than 500 μm and 300 μm or more, and particles (A4) having a particle diameter of less than 300 μm and 150 μm or more, more preferably three kinds As mentioned above, More preferably, 4 types are included.
The water-absorbing agent according to the present invention preferably contains 95% by weight or more of particles having a particle diameter of less than 850 μm and 150 μm or more, more preferably 97% by weight or more, and still more preferably 98% by weight or more. By controlling to such a specific particle size, high physical properties are achieved with sanitary materials.
[0069]
The water-absorbing agent according to the present invention preferably contains 0.1% by weight or more of each of the four types of particles A1 to A4, more preferably 1% by weight or more, and further preferably 3% by weight or more. In this case, the upper limit is not particularly limited, but preferably, the four types of particles A1 to A4 are each 99% by weight or less, more preferably 90% by weight or less, and still more preferably 80% by weight or less. By containing each particle size above a certain level, the water absorption speed depending on the surface area of the particles is controlled in a well-balanced manner.
(B) CRC
The water-absorbing agent according to the present invention preferably has an absorption capacity (Centrifuge Retention Capacity / CRC) of 30 g / g for 30 minutes under no pressure with respect to 0.90% by weight physiological saline. When the CRC is 31 g / g or more, it is critically superior in absorbing hygiene materials using a water-absorbing agent, and a compact sanitary material can be achieved. Further, a water-absorbing body (note that a water-absorbing body is a water-absorbing agent and This also means a reduction in the cost of a bodily fluid water-absorbing body containing other water-absorbing materials such as fibers. CRC is more preferably 32 g / g or more, further preferably 33 g / g or more, still more preferably 34 g / g or more, particularly preferably 35 g / g or more, and particularly preferably 36 g / g or more. If the absorption rate for 30 minutes under 0.90% by weight physiological saline is less than 31 g / g, the total amount of urine that can be absorbed by the water absorbent becomes small, and the urine absorbed by the water absorbent is a diaper. The return to the surface is very large. Furthermore, when trying to maintain the urine absorption amount required for the water absorbent body, the amount of water absorbent used in the water absorbent body increases, sanitary materials become bulky and heavy, leading to an increase in the cost of the water absorbent body. This is not preferable.
[0070]
(C) AAP
The water-absorbing agent according to the present invention preferably has an absorption capacity under pressure (Absorbency Against Pressure / AAP) of not less than 20 g / g at 4.83 kPa against 0.90 wt% physiological saline for 60 minutes. When the water-absorbing agent of the present invention is used as a part of the water absorbent body of a paper diaper due to the AAP being 20 g / g or more, the effect of preventing the urine absorbed by the water absorbent body from returning to the surface of the diaper is very large. Become. The absorption capacity under pressure at 4.83 kPa for 0.90 wt% physiological saline for 60 minutes is more preferably 22 g / g or more, still more preferably 24 g / g or more, still more preferably 25 g / g or more, particularly preferably. 26 g / g, particularly preferably 27 g / g or more. When the absorption capacity under pressure at 4.83 kPa against 0.90% by weight physiological saline is less than 20 g / g, the effect of preventing the urine absorbed by the water absorbent from returning to the surface of the diaper is very small. This is not preferable.
[0071]
(D) SFC
The water-absorbing agent according to the present invention has a 0.69% by weight physiological saline flow conductivity (SFC) of 20 (unit: 10).^-7× cm^Three× s × g^-1) Or more. SFC has a great influence on the liquid permeability after swelling of the water-absorbing agent obtained in the present invention. In other words, for example, when the water-absorbing agent of the present invention is used for a part of the water absorbent body of a paper diaper, the liquid permeability is improved, the liquid is sufficiently distributed to the water absorbent body, the liquid absorption amount is increased, and the liquid leaks. The effect of preventing is significantly improved. SFC is more preferably 25 (unit: 10^-7× cm^Three× s × g^-1) Or more, more preferably 30 (unit: 10)^-7× cm^Three× s × g^-1) Or more, more preferably 35 (unit: 10)^-7× cm^Three× s × g^-1) Or more, particularly preferably 40 (unit: 10)^-7× cm^Three× s × g^-1) Or more, particularly preferably 50 (unit: 10)^-7× cm^Three× s × g^-1) That's it. SFC is 20 (unit: 10^-7× cm^Three× s × g^-1If it is smaller than, for example, the liquid permeability when used in a water absorbent body of a paper diaper is reduced, the liquid is localized in the water absorbent body, the amount of liquid absorbed is reduced, and the leakage of the liquid is increased. It is not preferable in that the performance of is significantly reduced.
[0072]
That is, it is preferable that the water-absorbing agent of the present invention has the following three physical properties in a well-balanced manner in addition to the particle size for use in sanitary materials. That is, it has been found that one or two of CRC, AAP, and SFC are not sufficiently suitable for sanitary materials only with high physical properties. These three physical properties are suitably applied not only to the water-absorbing agent having a specific neutralization index obtained by acid polymerization but also to a water-absorbing resin by a neutralization polymerization method not including a post-neutralization step.
Absorption capacity (CRC) for 30 minutes with no pressure against 0.90% by weight physiological saline is 31 g / g or more.
[0073]
Absorption capacity under load (AAP) at 4.83 kPa with respect to 0.90 wt% physiological saline is 24 g / g or more.
0.69 wt% saline flow conductivity (SFC) is 20 (unit: 10)^-7× cm^Three× s × g^-1)more than.
(E) SFC change index
In addition, in the water-absorbing resin (water-absorbing agent) particles, which have been conventionally evaluated and managed in the whole particle (Bulk), the present inventors have greatly different physical properties for each particle size of the water-absorbing resin (water-absorbing agent) particles, It was found that the difference in physical properties for each particle size caused a decrease in physical properties in sanitary materials. Since the water-absorbent particles contained in sanitary materials are microscopically different in particle size, the differences in the physical properties of individual sanitary materials derived from the particle size and the physical properties of the sanitary materials are due to the physical properties of the sanitary materials. Estimated to cause a decline.
[0074]
Therefore, the present inventors provide a water-absorbing agent having a small difference in physical properties for each particle size, particularly a small variation in SFC for each particle size.
The water absorbent according to the present invention preferably has an SFC change index defined by the following formula (1) of 0 to 25%.
SFC change index (%) = [(standard deviation of SFC of particles A1 to A4) / (SFC of the entire particulate water-absorbing agent)] × 100 (1)
In this SFC change index and SFC variation coefficient described later, the SFC standard deviation of the particles A1 to A4 classifies the water-absorbing agent particles, and 2 to 4 types of particles existing among the particles A1 to A4 in the water-absorbing agent. Then, the SFC for each particle size obtained is measured once, and the standard deviation is calculated from the two to four types of SFC values. In addition, the average value is similarly calculated from the two to four types of SFC values.
[0075]
This SFC change index represents the variation of SFC for each particle size. When the SFC change index is 0 to 25%, the water absorbent body has more uniform liquid permeability, and the liquid is dispersed throughout the water absorbent body. It becomes easy to do and it becomes the effect of preventing the leakage of the liquid. The SFC change index is more preferably 0 to 23%, further preferably 0 to 20%, still more preferably 0 to 18%, particularly preferably 0 to 15%, and particularly preferably 0 to 10%. If the SFC change index is larger than 25%, for example, when a water absorbing agent is used for the water absorbent body of a paper diaper, the water absorbent body has a variation in liquid permeability, and it becomes difficult for the liquid to be dispersed throughout the water absorbent body. It is not preferable in terms of generation and reduction of the water absorption amount of the water absorbent.
[0076]
(F) SFC coefficient of variation
The water absorbing agent according to the present invention preferably has an SFC variation coefficient defined by the following formula (2) of 0 to 0.25.
SFC variation coefficient = (standard deviation of SFC of particles A1 to A4) / (average value of SFC of particles A1 to A4) (2)
This SFC variation coefficient and the following SFC variation rate also represent a small difference in SFC for each particle size, and the SFC variation coefficient is 0 to 0.25, so that the SFC of each particle size (for example, A1 to A4) For example, when manufacturing a water absorbent body of a paper diaper using the water absorbent of the present invention, the liquid permeability in the water absorbent body is uniform, and even if each of the water absorbent bodies is compared, the paper diaper As a result, it is possible to produce a disposable diaper with stable quality. The SFC coefficient of variation is more preferably 0 to 0.23, still more preferably 0 to 0.20, even more preferably 0 to 0.18, particularly preferably 0 to 0.15, and particularly preferably 0 to 0.0. 10. When the SFC coefficient of variation is larger than 0.25 and / or when the SFC coefficient of variation is less than 0.65, the liquid permeability of the hygroscopic material (especially paper diaper) using the water absorbing agent in the water absorbing body becomes uneven. Furthermore, even if each of the water absorbent bodies is compared, it is not preferable in that the performance variation of the disposable diaper becomes large and it becomes impossible to manufacture a disposable diaper having a stable quality.
[0077]
(G) SFC fluctuation rate
That is, the water absorbing agent according to the present invention preferably has an SFC fluctuation rate defined by the following formula (3) of 0.65 to 1.00.
SFC variation rate = (minimum SFC among particles A1 to A4 SFC) / (maximum SFC among particles A1 to A4 SFC) (3)
This SFC variation rate similarly represents a small difference in SFC for each particle size, preferably 0.70 to 1.00, still more preferably 0.75 to 1.00, and particularly preferably 0.80 to 1. 00.
[0078]
(H) Surface soluble amount
The water-absorbing agent of the present invention preferably has a surface layer soluble content of 6.0% by weight or less (for water-absorbing agent). The surface layer soluble content is preferably 5.5% by weight or less, more preferably 5.0% by weight or less, still more preferably 4.5% by weight or less, and particularly preferably 4.0% by weight or less.
The surface soluble component defined by the measurement method of the present application is the amount of soluble component corresponding to actual use for sanitary materials, and is more excellent in water absorption capability in sanitary materials. In other words, conventionally, many methods for measuring water-soluble components (US Re 32649, EDANA method, etc.) have been known. It was found that the amount of solubles in excess of the amount of minutes was measured. And it has been found that the method of the present invention is the most model for practical use in sanitary materials.
[0079]
(I) Continuous production system SFC standard deviation
The water absorbing agent according to the present invention preferably has a continuous production system SFC standard deviation defined by the following formula (4) of 5.0 or less.
Standard deviation of continuous production system SFC = Standard deviation of SFC of each lot (4)
(However, each lot is 20 kg or more. The number of lots is 10 or more.)
The continuous production system means that a water absorbing agent is continuously produced in one line for 24 hours or more, or 10 t or more. In addition, in the continuous production system, polymerization, drying, pulverization, surface treatment, etc., which are the basic steps of the method for producing a water-absorbing agent, may be performed continuously or batchwise (for example, continuous in the polymerization step). The interval between each step is 24 hours or less, preferably 12 hours or less, more preferably 6 hours or less, and particularly preferably 3 hours or less.
[0080]
Each lot is preferably 20 kg to 100 t, more preferably 0.1 t to 50 t, and still more preferably 0.5 t to 25 t.
The Lot number is preferably 20 or more, more preferably 30 or more, still more preferably 50 or more, and particularly preferably 100 or more.
This continuous production system SFC standard deviation represents the variation in the SFC value of each lot in the continuous production of the water-absorbing agent. When the continuous production system SFC standard deviation is 5.0 or less, the variation in SFC for each lot is reduced. For example, when a water absorbent body of a paper diaper is manufactured using the water-absorbing agent of the present invention, a stable quality paper diaper can be manufactured. The continuous production system SFC standard deviation is more preferably 4.5 or less, still more preferably 4.3 or less, even more preferably 4.0 or less, particularly preferably 3.5 or less, particularly more preferably 3.0 or less, Most preferably, it is 2.5 or less. When the continuous production system SFC standard deviation is larger than 5.0, it is not preferable in that a disposable diaper having a stable quality cannot be manufactured.
[0081]
The above-mentioned various physical properties are important physical properties that correlate with the actual use results (absorbed amount of diapers, leakage, etc.) when the water-absorbing agent is used as a sanitary material. Especially good. These measuring methods are described in the Examples.
The water-absorbing agent according to the present invention preferably has the various characteristics described above, and as a particularly preferred configuration, any one or more of the above formulas (1), (2), (4), more preferably It is a water absorbing agent satisfying two or more, more preferably all three.
That is, the water-absorbing agent according to the present invention is a particulate water-absorbing agent mainly composed of a water-absorbing resin having a crosslinked structure obtained by polymerizing an unsaturated monomer component,
The particulate water-absorbing agent contains 90% by weight or more of particles having a particle size of less than 850 μm and 150 μm or more, and is a particle (A1) having a particle size of less than 850 μm and 600 μm or more, and a particle size of less than 600 μm and 500 μm. Including at least two or more selected from the above particles (A2), particles having a particle size of less than 500 μm and not less than 300 μm (A3), particles having a particle size of less than 300 μm and not less than 150 μm (A4),
Furthermore, it is a water absorbing agent characterized by satisfying the following physical properties.
[0082]
Absorption capacity (CRC) for 30 minutes with no pressure against 0.90% by weight physiological saline is 31 g / g or more.
Absorption capacity under pressure (AAP) for 60 minutes at 4.83 kPa with respect to 0.90% by weight physiological saline is 24 g / g or more.
0.69 wt% saline flow conductivity (SFC) is 20 (unit: 10)^-7× cm^Three× s × g^-1)more than.
SFC change index defined by the following formula (1) is 0 to 25%.
SFC change index (%) = [(standard deviation of SFC of particles A1 to A4) / (SFC of the entire particulate water-absorbing agent)] × 100 (1)
Another water absorbent according to the present invention is a particulate water absorbent mainly composed of a water absorbent resin having a crosslinked structure obtained by polymerizing an unsaturated monomer component,
The particulate water-absorbing agent contains 90% by weight or more of particles having a particle size of less than 850 μm and 150 μm or more, and is a particle (A1) having a particle size of less than 850 μm and 600 μm or more, and a particle size of less than 600 μm and 500 μm. Including at least two or more selected from the above particles (A2), particles having a particle size of less than 500 μm and not less than 300 μm (A3), particles having a particle size of less than 300 μm and not less than 150 μm (A4),
Furthermore, it is a water absorbing agent characterized by satisfying the following physical properties.
[0083]
Absorption capacity (CRC) for 30 minutes with no pressure against 0.90% by weight physiological saline is 31 g / g or more.
Absorption capacity under pressure (AAP) for 60 minutes at 4.83 kPa with respect to 0.90% by weight physiological saline is 24 g / g or more.
0.69 wt% saline flow conductivity (SFC) is 20 (unit: 10)^-7× cm^Three× s × g^-1)more than.
The SFC variation coefficient defined by the following formula (2) is 0 to 0.25.
SFC variation coefficient = (standard deviation of SFC of particles A1 to A4) / (average value of SFC of particles A1 to A4) (2)
Further, another water-absorbing agent according to the present invention is a particulate water-absorbing agent mainly composed of a water-absorbing resin having a crosslinked structure obtained by polymerizing an unsaturated monomer component,
The particulate water-absorbing agent contains 90% by weight or more of particles having a particle size of less than 850 μm and 150 μm or more, and is a particle (A1) having a particle size of less than 850 μm and 600 μm or more, and a particle size of less than 600 μm and 500 μm. Including at least two or more selected from the above particles (A2), particles having a particle size of less than 500 μm and not less than 300 μm (A3), particles having a particle size of less than 300 μm and not less than 150 μm (A4),
Furthermore, it is a water absorbing agent characterized by satisfying the following physical properties.
[0084]
Absorption capacity (CRC) for 30 minutes with no pressure against 0.90% by weight physiological saline is 31 g / g or more.
Absorption capacity under pressure (AAP) for 60 minutes at 4.83 kPa with respect to 0.90% by weight physiological saline is 24 g / g or more.
0.69 wt% saline flow conductivity (SFC) is 20 (unit: 10)^-7× cm^Three× s × g^-1)more than.
Standard production system SFC standard deviation defined by the following formula (4) is 5.0 or less.
Standard deviation of continuous production system SFC = Standard deviation of SFC of each lot (4)
(However, CRC, AAP, and SFC are averages of lots, and each lot is 20 kg or more. The number of lots is 10 or more.)
Still another water-absorbing agent according to the present invention is a particulate water-absorbing agent obtained by polymerizing a monomer containing an acid group-containing monomer (salt) and further surface-crosslinking a water-absorbing resin obtained by post-neutralization. There,
The neutralized index of the particulate water-absorbing agent or water-absorbing resin is 15 or more, and the absorption capacity under pressure (AAP) for 60 minutes at 4.83 kPa with respect to 0.90 wt% physiological saline after surface crosslinking is 20 ( g / g) or more, which is a water-absorbing agent.
[0085]
In the above water-absorbing agent, CRC, AAP, SFC, SFC change index, SFC variation coefficient and the like are preferably in the above-mentioned range, and the novel water-absorbing agent of the present invention is, for example, the above-described method for producing a water-absorbing agent of the present invention. can get. The water-absorbing agent of the present invention has a very high CRC, AAP, and SFC and maintains high physical properties in a well-balanced manner. Further, since the change in physical properties for each particle size is unprecedented, it has high physical properties under any sanitary material usage conditions. Is an excellent water-absorbing agent.
According to the present invention, it is possible to easily produce a water-absorbing agent having good absorption characteristics with an excellent balance of absorption capacity under no pressure, absorption capacity under pressure, and physiological saline flow inductivity. Widely used in water-retaining agents, industrial water-retaining agents, moisture-absorbing agents, dehumidifying agents, building materials, etc., but these water-absorbing agents are particularly suitable for use in sanitary materials for absorbing feces, urine or blood, such as disposable diapers and sanitary napkins. It is done. Further, since the water-absorbing agent of the present invention is excellent in the above-mentioned various physical properties in a well-balanced manner, sanitary materials generally have a high concentration, for example, 30 to 100 wt. %, Preferably in the range of 40 to 100% by weight, more preferably in the range of 50 to 95% by weight. Further, the structure of the water-absorbing body in the sanitary material is not particularly limited as long as it is a structure used for general water-absorbing articles. For example, a so-called water-absorbing agent is disposed between hydrophilic fiber materials formed into a sheet shape. Examples include a water absorbent body having a sandwich structure and a water absorbent body having a so-called blend structure formed by mixing a hydrophilic fiber material and a water absorbent.
[0086]
【Example】
Hereinafter, although an example and a comparative example explain the present invention still in detail, the present invention is not limited to these examples. The various performances of the water absorbent resin or water absorbent were measured by the following methods.
In the case of a water-absorbing agent used as a final product such as sanitary material, the water-absorbing agent absorbs moisture. Therefore, after appropriately separating the water-absorbing agent from the final product and drying under reduced pressure at low temperature (for example, 1 mmHg or less, 60 ° C. 12 hours). In addition, the water content of the water-absorbent resins used in the examples and comparative examples of the present invention were all 6% by weight or less.
[0087]
Furthermore, when measuring SFC by particle size in (4) described later, in the water absorbent used as a final product such as sanitary material, SFC is measured after the above operation. When measuring the water-absorbing agent manufactured in the laboratory, in order to correlate with the damage of actual production and actual use, all of the water-absorbing agent after mechanical damage described in (5) below, SFC by particle size, classification Measure SFC before starting.
(1) Absorption capacity under no pressure (absorption capacity / CRC for 30 minutes under no pressure with respect to 0.90% by weight physiological saline)
Under conditions of room temperature (20 to 25 ° C.) and humidity of 50 RH%, 0.20 g of a water-absorbing resin or water-absorbing agent is uniformly put in a non-woven bag (60 mm × 60 mm) and sealed, and then 0.9 weight at room temperature. It was immersed in% physiological saline. After 30 minutes, the bag was pulled up, drained at 250 G for 3 minutes using a centrifuge (manufactured by Kokusan Co., Ltd., centrifuge: model H-122), and the weight W1 (g) of the bag was measured. Further, the same operation was performed without using a water absorbent resin or a water absorbent, and the weight W0 (g) at that time was measured. And from these W1 and W0, the absorption capacity (g / g) under no pressure was calculated according to the following formula.
[0088]
Absorption capacity under no pressure (g / g) = (W1 (g) -W0 (g)) / weight of water absorbent resin or water absorbent (g)
(2) Absorption capacity under pressure (absorption capacity under pressure / AAP for 60 minutes at 4.83 kPa against 0.90 wt% physiological saline)
A stainless steel 400 mesh wire mesh (mesh size 38 μm) is fused to the bottom of a plastic support cylinder with an inner diameter of 60 mm, and water is absorbed on the mesh under conditions of room temperature (20-25 ° C.) and humidity 50 RH%. 0.90 g of the agent was uniformly sprayed, and the outer diameter was adjusted to be able to uniformly apply a load of 4.83 kPa (0.7 psi) to the water-absorbing agent. A piston and a load, in which a gap with the cylinder does not occur and the vertical movement is not hindered, were placed in this order, and the weight Wa (g) of this measuring device set was measured.
[0089]
A glass filter of 90 mm in diameter (manufactured by Mutual Riken Glass Co., Ltd., pore diameter: 100 to 120 μm) is placed inside a petri dish having a diameter of 150 mm, and 0.90 wt% physiological saline (20 to 25 ° C.) is glass. It added so that it might become the same level as the upper surface of a filter. On top of that, a sheet of filter paper having a diameter of 90 mm (ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No. 2), thickness 0.26 mm, retention particle diameter 5 μm) was placed so that the entire surface was wetted, and Excess liquid was removed.
The set of measuring devices was placed on the wet filter paper, and the liquid was absorbed under load. After 1 hour, the measuring device set was lifted and its weight Wb (g) was measured. And the absorption capacity | capacitance (g / g) under pressure was computed from Wa and Wb according to following Formula.
[0090]
Absorption capacity under pressure (g / g)
= (Wa (g) -Wb (g)) / weight of water-absorbing agent ((0.9) g)
(3) Weight average particle diameter
The water-absorbing resin powder or water-absorbing agent was sieved with JIS standard sieves having an opening of 850 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, 75 μm, etc., and the residual percentage R was plotted on logarithmic probability paper. Thereby, the weight average particle diameter (D50) was read.
The method of sieving and classifying SFC for each particle size described later is as follows: water-absorbent resin powder or 10.0 g of water-absorbing agent is opened at room temperature (20 to 25 ° C.) and humidity of 50 RH%. 850 μm, 600 μm, 500 μm, 300 μm, 150 μm JIS standard sieve (THE IIDA TESTING SIVE: diameter 8 cm) was charged for 10 minutes with vibration classifier (IIDA SIEVE SHAKER, TYPE: ES-65 type, SER No. 0501). , Classification was done.
[0091]
(4) 0.69 wt% saline flow conductivity (SFC)
It carried out according to the physiological saline flow inductivity (SFC) test of Tokuheihei 9-509591.
Using the apparatus shown in FIG. 1, the water-absorbing agent (0.900 g) uniformly placed in the container 40 is swollen in the artificial urine (1) for 60 minutes under a pressure of 0.3 psi (2.07 kPa), The height of the gel layer is recorded, and then 0.69 wt% saline 33 is passed through the swelled gel layer from the tank 31 at a constant hydrostatic pressure under a pressure of 0.3 psi (2.07 kPa). . The SFC test was performed at room temperature (20-25 ° C.). Using a computer and a balance, the amount of liquid passing through the gel layer at 20 second intervals as a function of time is recorded for 10 minutes. Flow velocity F passing through swollen gel 44 (mainly between particles)_s(T) is determined in units of g / s by dividing the increased weight (g) by the increased time (s). The time at which a constant hydrostatic pressure and a stable flow rate were obtained was t_sAnd t_sAnd only the data obtained during 10 minutes is used for the flow rate calculation, t_sAnd F using the flow rate obtained during 10 minutes._sCalculate the value of (t = 0), ie the initial flow rate through the gel layer. F_s(T = 0) is F_s(T) Calculated by extrapolating the result of least squares versus time to t = 0.
[0092]

here,
F_s(T = 0): flow rate expressed in g / s
L₀: Height of gel layer in cm
ρ: density of NaCl solution (1.003 g / cm^Three)
A: Area above the gel layer in the cell 41 (28.27 cm²)
ΔP: Hydrostatic pressure applied to the gel layer (4920 dyne / cm²)
And the unit of SFC value is (10^-7× cm^Three× s × g^-1).
[0093]
As an apparatus shown in FIG. 1, a glass tube 32 is inserted into the tank 31, and the lower end of the glass tube 32 is filled with 0.69 wt% physiological saline 33 from the bottom of the swelling gel 44 in the cell 41. It was arranged so that it could be maintained at a height of 5 cm. 0.69 wt% physiological saline 33 in the tank 31 was supplied to the cell 41 through the L-shaped tube 34 with a cock. Under the cell 41, a container 48 for collecting the passed liquid is disposed, and the collection container 48 is installed on an upper pan balance 49. The inner diameter of the cell 41 is 6 cm. A 400 stainless steel wire mesh (aperture 38 μm) 42 was installed. There is a hole 47 sufficient for the liquid to pass through the lower part of the piston 46, and a glass filter 45 with good permeability is attached to the bottom so that the water absorbing agent or its swollen gel does not enter the hole 47. The cell 41 was placed on a table on which the cell was placed, and the surface of the table in contact with the cell was placed on a stainless steel wire mesh 43 that did not prevent liquid permeation.
[0094]
Artificial urine (1) is calcium chloride dihydrate 0.25 g, potassium chloride 2.0 g, magnesium chloride hexahydrate 0.50 g, sodium sulfate 2.0 g, ammonium dihydrogen phosphate 0.85 g, What added 0.15 g of hydrogen ammonium diphosphate and 994.25 g of pure waters was used.
(5) Mechanical damage test
A glass container (Yamamura Glass mayonnaise bottle, trade name: A-29) shown in FIG. 2 was charged with 30 g of a water-absorbing agent and 10 g of glass beads (soda-lime glass beads for precision fractional filling with a ball diameter of about 6 mm). This was sandwiched and fixed between clamps provided in a disperser (manufactured by Toyo Seiki Seisakusho, No. 488 test disperser) shown in FIG. 3, and a vibration with a vibration rotational speed of 750 cpm was applied at 100 V / 60 Hz for 10 minutes. As a result, the container fixed to the disperser tilts and moves 12.5 ° to the left and right (total 25 °) with respect to the mounting surface of the clamp in the disperser, and at the same time, vibrates to the front and rear by 8 mm (total 16 mm). By doing so, an impact is given to the water-absorbing agent inside the container. The above impact is a force empirically determined as representative of the impact force received by the water absorbent during the manufacturing process of the water absorbent, but can also be widely applied to damage after transportation and water absorber production. It is. In the present invention, when mechanical damage is caused, it is particularly assumed that the water absorbing agent is manufactured and the water absorbing body is manufactured. Further, the SFC change index, the SFC variation coefficient, and the SFC variation rate are indicators for measuring the variation in the performance of the water absorbent within the water absorbent. Therefore, when measuring physical properties by particle size, all water absorbents manufactured in a laboratory scale (the amount of water absorbent obtained in one manufacturing process is 20 kg or less) must cause the mechanical damage. .
[0095]
(6) Amount of soluble component (water-soluble component)
A plastic container with a lid with a capacity of 250 ml is weighed 184.3 g of 0.9% by weight physiological saline solution (saline), and 1.00 g of a water absorbent resin is added to the aqueous solution and stirred for 16 hours. Soluble components were extracted. Filtration of this extract using one sheet of filter paper (ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No. 2), thickness 0.26 mm, retained particle diameter 5 μm) gave 50. 0 g was measured and used as a measurement solution.
First, the physiological saline alone is titrated to pH 10 with a 0.1N aqueous NaOH solution, and then titrated to a pH 2.7 with a 0.1N aqueous HCl solution (blank titration [[bNaOH] ml, [bHCl] ml).
[0096]
The titration ([NaOH] ml, [HCl] ml) was determined by performing the same titration operation on the measurement solution.
For example, in the case of a water-absorbing resin composed of a known amount of acrylic acid and its sodium salt, based on the average molecular weight of the monomer and the titration amount obtained by the above operation, the soluble content in the water-absorbing resin is calculated as follows: Can be calculated. In the case of an unknown amount, the average molecular weight of the monomer is calculated using the neutralization rate obtained by titration.
Soluble content (% by weight) = 0.1 × (average molecular weight) × 184.3 × 100 × ([HCl] − [bHCl]) / 1000 / 1.0 / 50.0
Neutralization rate (mol%) = (1 − ([NaOH] − [bNaOH]) / ([HCl] − [bHCl])) × 100
(7) Amount of surface layer soluble component (water soluble component)
100 g of a 0.50 wt% physiological saline solution was weighed into a 250 ml capacity plastic container with a lid, 0.50 g of a water absorbing agent was added to the aqueous solution, and the surface soluble component in the water absorbing agent was extracted for 1 hour. In this extraction operation, stirring is performed only for the purpose of dispersing the initial water-absorbing agent and homogenizing the last liquid, and stirring is not performed except for the above. Specifically, the surface soluble component is extracted by standing, and is stirred for 1 minute before and after extraction (stirring speed: 400 rpm, stirrer: made of Teflon (registered trademark) (2.5 cm)). Filtration of this extract using one sheet of filter paper (ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No. 2), thickness 0.26 mm, retained particle diameter 5 μm) gave 50. 0 g was measured and used as a measurement solution.
[0097]
First, only 0.5 wt% NaCl aqueous solution is titrated to pH 10 with 0.1N NaOH aqueous solution, and then titrated to pH 2.7 with 0.1N HCl aqueous solution to give an empty titration ([bNaOH] ml). [BHCl] ml).
The titration ([NaOH] ml, [HCl] ml) was determined by performing the same titration operation on the measurement solution.
For example, in the case of a water-absorbing agent comprising a known amount of acrylic acid and its sodium salt, based on the average molecular weight of the monomer and the titration amount obtained by the above operation, the amount of soluble matter in the surface layer in the water-absorbing agent is calculated by the following formula: Can be calculated. In the case of an unknown amount, the average molecular weight of the monomer is calculated using the neutralization rate obtained by titration.
[0098]
Surface layer soluble content (% by weight) = 0.1 × (average molecular weight) × 100 × 100 × ([HCl] − [bHCl]) / 1000 / 0.5 / 50.0
Neutralization rate (mol%) = (1 − ([NaOH] − [bNaOH]) / ([HCl] − [bHCl])) × 100
(8) Neutralization index
In accordance with JP-A-10-101735 and claim 3 thereof (European Patent Publication No. 0882502 and claims 2 to 4 thereof), the neutralization index of the water-absorbent resin powder and the water-absorbing agent was determined.
[0099]
That is, 200 particles of water-absorbing resin powder or water-absorbing agent classified to 300 to 600 μm with a JIS standard sieve are placed in a 1.6 mm thick plastic plate having a 20 mm × 20 mm opening with a cover glass attached thereto, Add 0.2 ml deionized water. Furthermore, 0.05 ml of a 1.5: 1 mixed solution of 0.1 wt% ethanol solution of bulumthymol blue (BTB) and 0.1 wt% methyl red (MR) was added to the swollen gel with a micro syringe. Then, coloring of 200 particles was observed with a pH indicator. Thus, the number of particles neutralized inhomogeneously exceeding 20 mol% from the average neutralization rate of the water-absorbing resin or water-absorbing agent was determined (some of 200 particles). The number was determined as the neutralization index (first neutralization index / claim 3 in the above patent). Of course, the higher the neutralization index, the more uneven the neutralization of the water absorbent resin powder. See the above patent for details.
[0100]
  (ManufacturingExample 1): Production / neutralization polymerization of water absorbent resin powder (A)
  5500 g of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% (single quantity) in a reactor formed by attaching a lid to a 10-liter jacketed stainless steel double-arm kneader having two sigma-shaped blades 3.70 g of polyethylene glycol diacrylate (n = 9) was dissolved in a body concentration of 38% by weight and an average molecular weight of the monomer of 88.5) to prepare a reaction solution. Next, this reaction solution was degassed for 30 minutes in a nitrogen gas atmosphere. Subsequently, 28.3 g of a 10 wt% aqueous sodium persulfate solution and 2.1 g of a 1 wt% L-ascorbic acid aqueous solution were added to the reaction solution with stirring. Polymerization started after about 1 minute. And it superposed | polymerized at 20-95 degreeC, grind | pulverizing the produced | generated gel, 30 minutes after superposition | polymerization started, the water-containing gel-like crosslinked polymer (1) was taken out.
[0101]
The obtained hydrogel crosslinked polymer (1) had a diameter of about 5 mm or less. This finely divided hydrogel crosslinked polymer (1) was spread on a 50 mesh (mesh opening 300 μm) wire net and dried with hot air at 150 ° C. for 90 minutes. Next, the mixture was pulverized using a roll mill and further classified with a JIS standard sieve having openings of 850 μm and 106 μm to obtain a water absorbent resin powder (A) in which most of the particles were in the range of 850 μm to 106 μm.
The absorption capacity of the obtained water absorbent resin powder (A) under no pressure is 49 (g / g), the soluble content is 23% by weight, and the weight average particle diameter (D50) is in the range of 330 μm, 850 μm to 150 μm. The water absorbent resin powder was 97% by weight.
[0102]
  (ManufacturingExample 2): Production of water-absorbent resin powder (B) / neutralization polymerization
  5500 g of sodium acrylate aqueous solution having a neutralization rate of 71 mol% (single unit) in a reactor formed by attaching a cover to a stainless steel double-armed kneader with a volume of 10 liters and having two sigma blades A reaction solution was prepared by dissolving 8.05 g of polyethylene glycol diacrylate (n = 9) in a body concentration of 41% by weight and an average molecular weight of the monomer of 87.7). Next, this reaction solution was degassed for 30 minutes in a nitrogen gas atmosphere. Subsequently, 30.8 g of a 10 wt% aqueous sodium persulfate solution and 2.57 g of a 1 wt% L-ascorbic acid aqueous solution were added to the reaction solution with stirring, and polymerization started about 1 minute later. And it superposed | polymerized at 20-95 degreeC, grind | pulverizing the produced | generated gel, 30 minutes after superposition | polymerization started, the water-containing gel-like crosslinked polymer (2) was taken out.
[0103]
The obtained hydrogel crosslinked polymer (2) was subdivided to have a diameter of about 5 mm or less. This finely divided hydrogel crosslinked polymer (2) was spread on a 50 mesh (mesh opening 300 μm) wire mesh and dried with hot air at 180 ° C. for 50 minutes. Next, the mixture was pulverized using a roll mill and further classified with a JIS standard sieve having an opening of 850 μm to obtain a water-absorbent resin powder (B) in which most of the particles were in the range of 850 μm or less.
The absorption capacity of the obtained water absorbent resin powder (B) under no pressure is 36 (g / g), the soluble content is 10% by weight, and the weight average particle diameter (D50) is in the range of 450 μm, 850 μm to 150 μm. The water absorbent resin powder was 97% by weight.
[0104]
  (ManufacturingExample 3): Production example of water-absorbent resin powder (C) / neutralization polymerization
  ManufacturingIn Example 2, except that it was changed to 5.01 g of polyethylene glycol diacrylateManufacturingPolymerization, drying, pulverization and classification were carried out in the same manner as in Example 2 to obtain a water absorbent resin powder (C). The absorption capacity of the obtained water-absorbent resin powder (C) under no pressure is 39 (g / g), the soluble content is 13% by weight, and the weight average particle diameter (D50) is in the range of 450 μm, 850 μm to 150 μm. The water absorbent resin powder was 97% by weight.
  (ManufacturingExample 4): Production Example of Water Absorbent Resin Powder (D) / Neutralization Polymerization
  ManufacturingIn Example 2, except that it was changed to 5.01 g of polyethylene glycol diacrylateManufacturingPolymerization, drying and grinding were carried out in the same manner as in Example 2. The obtained pulverized product was further classified with a JIS standard sieve having openings of 600 μm and 300 μm to obtain water absorbent resin powder (D) in the range of 600 μm to 300 μm. The resultant water-absorbent resin powder (D) had an absorption capacity of 40 (g / g) under no pressure, a soluble content of 9% by weight, and a weight average particle size (D50) of 450 μm.
[0105]
  (referenceExample 1): Cross-linking treatment of water-absorbent resin powder (A) / with water-soluble inorganic base
  ManufacturingTo 100 g of the water-absorbent resin powder (A) obtained in Example 1, 0.027 g of ethylene glycol diglycidyl ether (Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.), 0.9 g of propylene glycol, 2.7 g of water, and carbonic acid After mixing the surface treating agent consisting of a mixed solution of sodium hydride 0.18 g, the mixture was heat treated at 210 ° C. for 35 minutes to obtain a water absorbing agent (1). The obtained water-absorbing agent (1) was also in the form of powder. Table 1 shows the results of measuring the absorption capacity under no pressure, the absorption capacity under pressure, and the saline flow conductivity.
[0106]
  (referenceExample 2): Cross-linking treatment of water-absorbent resin powder (A) / with water-soluble inorganic base
  referenceIn Example 1, a water-absorbing agent (2) was obtained in the same manner except that 0.09 g of sodium carbonate was used instead of sodium bicarbonate. Table 1 shows the results of measurement of absorption capacity under no pressure, absorption capacity under pressure, and physiological saline flow conductivity.
  (Comparative Example 1): Crosslinking treatment of water-absorbent resin powder (A) / no water-soluble inorganic base
  referenceIn Example 1, a comparative water-absorbing agent (1) was obtained in the same manner except that 0.81 g of isopropyl alcohol was used instead of sodium bicarbonate. Table 1 shows the results of measurement of absorption capacity under no pressure, absorption capacity under pressure, and physiological saline flow conductivity.
[0107]
  (Comparative Example 2): Crosslinking treatment of water-absorbent resin powder (A) / no water-soluble inorganic base
  referenceIn Example 1, a comparative water-absorbing agent (2) was obtained in the same manner except that sodium bicarbonate was not used. Table 1 shows the results of measurement of absorption capacity under no pressure, absorption capacity under pressure, and physiological saline flow conductivity.
  (referenceExample 3): Cross-linking treatment of water-absorbent resin powder (B) / with water-soluble inorganic base
  ManufacturingTo 100 g of the water-absorbent resin powder (B) obtained in Example 2, 0.384 g of 1,4-butanediol, 0.6 g of propylene glycol, 3.28 g of water, and 0.3 g of a 24 wt% aqueous sodium hydroxide solution (solid content) 0.072 g) was mixed with the surface treatment agent, and then the mixture was heat treated at 212 ° C. for 30 minutes to obtain a water absorbing agent (3). The obtained water-absorbing agent (3) was also in the form of a powder. The results of measuring the absorption capacity under no pressure, the absorption capacity under pressure, and the physiological saline flow conductivity are shown in Table 1.
[0108]
  (Comparative Example 3): Crosslinking treatment of water-absorbent resin powder (B) / no water-soluble inorganic base
  referenceA comparative water-absorbing agent (3) was obtained in the same manner as in Example 3, except that the 24 wt% aqueous sodium hydroxide solution was not used. Table 1 shows the results of measurement of absorption capacity under no pressure, absorption capacity under pressure, and physiological saline flow conductivity.
  (referenceExample 4): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base
  ManufacturingSurface treatment comprising a mixed solution of 0.384 g of 1,4-butanediol, 0.6 g of propylene glycol, 3.28 g of water, and 0.24 g of sodium bicarbonate to 100 g of the water absorbent resin powder (C) obtained in Example 3 After mixing the agent, the mixture was heat-treated at 212 ° C. for 40 minutes to obtain a water-absorbing agent (4). The obtained water-absorbing agent (4) was also in the form of a powder. The results of measuring the absorption capacity under no pressure, the absorption capacity under pressure, and the physiological saline flow conductivity are shown in Table 1.
[0109]
  (referenceExample 5): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base
  referenceIn Example 4, a water absorbing agent (5) was obtained in the same manner except that 0.12 g of sodium carbonate was used instead of using sodium hydrogen carbonate. Table 1 shows the results of measurement of absorption capacity under no pressure, absorption capacity under pressure, and physiological saline flow conductivity.
  (referenceExample 6): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base
  referenceIn Example 4, a water-absorbing agent (6) was obtained in the same manner except that 0.3 g of a 24 wt% aqueous sodium hydroxide solution (solid content: 0.072 g) was used instead of using sodium bicarbonate. Table 1 shows the results of measurement of absorption capacity under no pressure, absorption capacity under pressure, and physiological saline flow conductivity.
[0110]
  (Comparative Example 4): Crosslinking treatment of water-absorbent resin powder (C) / without water-soluble inorganic base
  referenceIn Example 4, a comparative water absorbing agent (4) was obtained in the same manner except that sodium bicarbonate was not used. Table 1 shows the results of measurement of absorption capacity under no pressure, absorption capacity under pressure, and physiological saline flow conductivity.
  (referenceExample 7): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base
  referenceIn Example 4, a water absorbing agent (7) was obtained in the same manner except that the heat treatment time was 30 minutes. Table 1 shows the results of measurement of absorption capacity under no pressure, absorption capacity under pressure, and physiological saline flow conductivity.
[0111]
  (referenceExample 8): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base
  referenceIn Example 7, a water absorbing agent (8) was obtained in the same manner except that 0.12 g of sodium carbonate was used instead of sodium hydrogen carbonate. Table 1 shows the results of measurement of absorption capacity under no pressure, absorption capacity under pressure, and physiological saline flow conductivity.
  (referenceExample 9): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base
  referenceIn Example 7, a water-absorbing agent (9) was obtained in the same manner except that 0.3 g of a 24 wt% aqueous sodium hydroxide solution (solid content: 0.072 g) was used instead of using sodium bicarbonate. Table 1 shows the results of measurement of absorption capacity under no pressure, absorption capacity under pressure, and physiological saline flow conductivity. Moreover, the surface layer soluble content of the water absorbing agent (9) was 3.8% by weight.
[0112]
  (Comparative Example 5): Crosslinking treatment of water-absorbent resin powder (C) / without water-soluble inorganic base
  referenceIn Example 7, a comparative water-absorbing agent (5) was obtained in the same manner except that sodium bicarbonate was not used. Table 1 shows the results of measurement of absorption capacity under no pressure, absorption capacity under pressure, and physiological saline flow conductivity. Further, the surface layer soluble component of the comparative water-absorbing agent (5) was 6.5% by weight.
  (Comparative Example 6): Crosslinking treatment of water-absorbent resin powder (C) / without water-soluble inorganic base
  referenceIn Example 9, a comparative water absorbing agent (6) was prepared in the same manner except that 0.455 g of aluminum sulfate 14-18 hydrate was used in accordance with WO 00/53664 instead of the 24 wt% aqueous sodium hydroxide solution. Obtained. The results are shown in Table 1.
[0113]
  (referenceExample 10): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base
  ManufacturingTo 100 g of the water absorbent resin powder (C) obtained in Example 3, 0.784 g of ethylene glycol diglycidyl ether (Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.), 4.0 g of water, and 24% by weight sodium hydroxide After mixing the surface treating agent which consists of 0.5 g of aqueous solution (solid content 0.12g) liquid mixture, the water absorbing agent (10) was obtained by heat-processing a mixture for 40 minutes at 212 degreeC. The obtained water-absorbing agent (10) was also in the form of a powder. The results are shown in Table 1.
  (Comparative Example 7): Cross-linking treatment of water-absorbent resin powder (C) / no water-soluble inorganic base
  referenceA comparative water-absorbing agent (7) was obtained in the same manner as in Example 10 except that the 24 wt% aqueous sodium hydroxide solution was not used. The results are shown in Table 1.
[0114]
  (referenceExample 11): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base
  ManufacturingTo 100 g of the water-absorbent resin powder (C) obtained in Example 3, 0.4 g of 3-ethyl-3-oxetanemethanol, 3.0 g of water, and 0.3 g of a 24 wt% aqueous sodium hydroxide solution (solid content 0.072 g) After mixing the surface treatment agent consisting of the mixed solution, the mixture was heat-treated at 212 ° C. for 40 minutes to obtain a water-absorbing agent (11). The resultant water-absorbing agent (11) was also in the form of a powder. The results are shown in Table 1.
  (Comparative Example 8): Cross-linking treatment of water-absorbent resin powder (C) / no water-soluble inorganic base
  referenceA comparative water-absorbing agent (8) was obtained in the same manner as in Example 11 except that the 24 wt% aqueous sodium hydroxide solution was not used. The results are shown in Table 1.
[0115]
  (Example1): Water-absorbing resin powder (C) cross-linking treatment / with pH buffer
  ManufacturingTo 100 g of the water-absorbent resin powder (C) obtained in Example 3, 0.15 g of ethylene glycol diglycidyl ether (Denacol EX-810, manufactured by Nagase Kasei), 1.0 g of propylene glycol, 5.0 g of water, and dihydrogen phosphate After mixing the surface treatment agent consisting of a mixed solution of sodium dihydrate 0.5 g, the mixture was heat treated at 150 ° C. for 30 minutes to obtain a water absorbing agent (12). The obtained water-absorbing agent (12) was also in the form of a powder. The results are shown in Table 1.
  (Comparative Example 9): Cross-linking treatment of water-absorbent resin powder (C) / no pH buffering agent
  Example1In Comparative Example 1, a comparative water-absorbing agent (9) was obtained in the same manner except that sodium dihydrogen phosphate dihydrate was not used. The results are shown in Table 1.
[0116]
  (referenceExample12): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base
  referenceIn Example 9, a water absorbing agent (13) was obtained using the same method. The obtained water-absorbing agent (13) was subjected to the mechanical damage for 10 minutes, and then the water-absorbing agent (13) was subjected to measurement of the absorption capacity under no pressure, the absorption capacity under pressure, and the saline flow-inductivity. The results are shown in Table 2. Further, the obtained water-absorbing agent (13) was sieved with a JIS standard sieve (aperture 850 μm, 600 μm, 500 μm, 300 μm, 150 μm), and each particle (13-a) having a particle size of less than 850 μm and 600 μm or more was smaller than 600 μm. Particles (13-b) having a particle diameter of less than 500 μm and particles having a particle diameter of less than 500 μm (13-c), and particles having a particle diameter of less than 300 μm and having a particle diameter of not less than 150 μm (13-d) were obtained. Table 2 shows the results of measuring the obtained water-absorbing agents (13-a), (13-b), (13-c), and (13-d). Table 3 shows the results of calculating the SFC change index, SFC variation coefficient, and SFC variation rate.
[0117]
  (referenceExample13): Cross-linking treatment of water-absorbent resin powder (C) / with water-soluble inorganic base
  referenceA water absorbing agent (14) was obtained in the same manner as in Example 9 except that the heating time was 20 minutes. Table 2 shows the results of measuring the obtained water-absorbing agent (14) after giving the mechanical damage to the obtained water-absorbing agent (14) for 10 minutes. Further, the obtained water-absorbing agent (14) was sieved with a JIS standard sieve (aperture 850 μm, 600 μm, 500 μm, 300 μm, 150 μm), and each particle (14-a) having a particle size of less than 850 μm and 600 μm or more, and a particle diameter of less than 600 μm Particles (14-b) having a particle diameter of less than 500 μm and particles having a particle diameter of less than 500 μm (14-c) and particles having a particle diameter of less than 300 μm and having a particle diameter of 150 μm or more (14-d) were obtained. Table 2 shows the results of measuring the obtained water-absorbing agent (14-a), (14-b), (14-c), and (14-d). Table 3 shows the results of calculating the SFC change index, SFC variation coefficient, and SFC variation rate.
[0118]
(Comparative Example 10): Cross-linking treatment of water-absorbent resin powder (C) / no water-soluble inorganic base
In Comparative Example 5, a comparative water absorbing agent (10) was obtained using the same method. After giving mechanical damage to the obtained comparative water-absorbing agent (10) for 10 minutes, the comparative water-absorbing agent (10) has an absorption capacity under no pressure, an absorption capacity under pressure, and saline flow conductivity. The measurement results are shown in Table 2. Further, the comparative water-absorbing agent (10) thus obtained was sieved with a JIS standard sieve (mesh opening 850 μm, 600 μm, 500 μm, 300 μm, 150 μm), and each particle (10-a) having a particle size of less than 850 μm and 600 μm or more was obtained. Particles (10-b) having a particle size of less than 600 μm and 500 μm or more, particles (10-c) having a particle size of less than 500 μm and 300 μm or more, and particles (10-d) having a particle size of less than 300 μm and 150 μm or more were obtained. Table 2 shows the results obtained by measuring the obtained comparative water-absorbing agent (10-a), (10-b), (10-c), and (10-d). Table 3 shows the results of calculating the SFC change index, SFC variation coefficient, and SFC variation rate.
[0119]
(Comparative Example 11): Commercially available water absorbing agent
A water absorbing agent was taken out from a diaper of Pampers Active Fit (manufactured by P & G, purchased on December 5, 2001) commercially available in Germany to obtain a comparative water absorbing agent (11). Table 2 shows the results of measuring the absorption capacity under no pressure, the absorption capacity under pressure, and the saline flow conductivity of the comparative water-absorbing agent (11) obtained. Further, the comparative water-absorbing agent (11) thus obtained was sieved with a JIS standard sieve (aperture 850, 600, 500, 300, 150 μm), and each particle (11-a) having a particle size of less than 850 μm and 600 μm or more was measured. Particles (11-b) having a particle diameter of less than 600 μm and 500 μm or more, particles (11-c) having a particle diameter of less than 500 μm and 300 μm or more, and particles (11-d) having a particle diameter of less than 300 μm and 150 μm or more were obtained. Table 2 shows the results obtained by measuring the obtained water-absorbing agent (11-a), (11-b), (11-c), and (11-d). Table 3 shows the results of calculating the SFC change index, SFC variation coefficient, and SFC variation rate.
[0120]
(Comparative Example 12): Commercially available water-absorbing agent
A water absorbing agent was taken out from a diaper of “Pampers Sarasara Care” (P & G, purchased in December 1997) that was commercially available in Japan, and used as a comparative water absorbing agent (12). Table 2 shows the results of measuring the absorption capacity under no pressure, the absorption capacity under pressure, and the saline flow conductivity of the comparative water-absorbing agent (12).
Further, the obtained water-absorbing agent (12) for comparison was sieved with a JIS standard sieve (aperture 850, 600, 500, 300, 150 μm), and each particle (12-a) was less than 850 μm and 600 μm or more, and the particle diameter was 600 μm. Particles (12-b) having a particle diameter of less than 500 μm, particles (12-c) having a particle diameter of less than 500 μm and having a particle diameter of less than 300 μm, and particles (12-d) having a particle diameter of less than 300 μm were obtained. Results of measuring the absorption capacity under no pressure, the absorption capacity under pressure, and the saline flow conductivity of the obtained water-absorbing agents (12-a), (12-b), (12-c), and (12-d) Are shown in Table 2. Table 3 shows the results of calculating the SFC change index, SFC variation coefficient, and SFC variation rate.
[0121]
  (referenceExample14): Cross-linking treatment of water-absorbent resin powder (D) / with water-soluble inorganic base
  ManufacturingTo 100 g of the water-absorbent resin powder (D) obtained in Example 4, 0.384 g of 1,4-butanediol, 0.6 g of propylene glycol, 3.28 g of water, and 0.3 g of a 24 wt% sodium hydroxide aqueous solution (solid content) 0.072 g) was mixed with the surface treatment agent, and then the mixture was heat-treated at 212 ° C. for 20 minutes to obtain a water absorbing agent (15). Table 2 shows the results of measuring the obtained water-absorbing agent (15) after giving the mechanical damage to the obtained water-absorbing agent (15) for 10 minutes. Further, the obtained water-absorbing agent (15) was sieved with a JIS standard sieve (mesh size 850 μm, 600 μm, 500 μm, 300 μm, 150 μm), and each particle (15-b) having a particle diameter of less than 600 μm and 500 μm or more was measured. Were less than 500 μm and particles (15-c) of 300 μm or more were obtained. Table 2 shows the results obtained by measuring the obtained water-absorbing agents (15-b) and (15-c). Table 3 shows the results of calculating the SFC change index, SFC variation coefficient, and SFC variation rate.
[0122]
  (referenceExample15): Cross-linking treatment of water-absorbent resin powder (D) / with water-soluble inorganic base
  referenceExample14The water absorbing agent (16) was obtained in the same manner except that the heating time was 40 minutes. Table 2 shows the results of measuring the obtained water-absorbing agent (16) after giving the mechanical damage to the obtained water-absorbing agent (16) for 10 minutes. Further, the obtained water-absorbing agent (16) was sieved with a JIS standard sieve (mesh size: 850 μm, 600 μm, 500 μm, 300 μm, 150 μm), and each of the particles (16-b) having a particle diameter of less than 600 μm and 500 μm or more was measured. Were less than 500 μm and particles (16-c) of 300 μm or more were obtained. Table 2 shows the results of measuring the obtained water-absorbing agents (16-b) and (16-c). Table 3 shows the results of calculating the SFC change index, SFC variation coefficient, and SFC variation rate.
[0123]
  (Comparative Examples 13 to 16): Commercially available water-absorbing agent
  As a water-absorbing agent (water-absorbing resin) actually used, a water-absorbing resin was taken out from a commercially available paper diaper in 2001 and used as comparative water-absorbing agents (13) to (16). Table 4 shows the results of measuring the absorption capacity under no pressure, the absorption capacity under pressure, and the saline flow conductivity of the comparative water-absorbing agents (13) to (16).
  (ManufacturingExample 5): Production of water-absorbent resin powder (E) / post-neutralization by acid type polymerization
  A 2 L plastic container was mixed with 252.2 g of acrylic acid, 1.1 g of N, N′-methylenebisacrylamide, and 998.4 g of water to prepare a reaction solution. Next, this reaction solution was degassed for 30 minutes in a nitrogen gas atmosphere. Subsequently, the reaction solution was mixed with 15 wt% 2,2′-azobis (2-amidinopropane) dihydrochloride 5.1 g, 10 wt% L-ascorbic acid aqueous solution 0.63 g, and 7 wt% hydrogen peroxide aqueous solution 3. 6 g was added to initiate the polymerization. Polymerization was carried out at 16 to 74 ° C., and the hydrogel crosslinked polymer (5) was taken out 3 hours after the start of the polymerization. After cutting the obtained polymer (5) into about 5 cm square, 15.0 g of a 48 wt% sodium hydroxide aqueous solution with an amount of neutralization of 65 mol% was mixed with 1000 g of the polymer (5), and the die diameter was further reduced. It was set as the pulverized gel finely divided by passing through a 9.5 mm meat chopper. The obtained crushed gel was spread on a 50 mesh (mesh opening 300 μm) wire mesh and dried with hot air at 170 ° C. for 40 minutes. Next, the mixture was pulverized using a roll mill, and further classified with a JIS standard mesh having openings of 500 μm and 300 μm to obtain a water absorbent resin powder (E) in which most of the particles were in the range of 500 μm to 300 μm. The resultant water-absorbent resin powder (E) had an absorption capacity of 49 (g / g) under no pressure and a soluble content of 6% by weight.
[0124]
  Furthermore, in order to investigate the uniformity of the neutralization rate of the obtained particles, 200 particles were swollen and further neutralized by adding 0.1 wt% ethanol solution of bromothymol blue and methyl red as pH indicators. The index (Claim 3 of JP-A-10-101735) was measured. as a result,ManufacturingIn the water-absorbent resin powders (A), (F), and (G) obtained from the neutralization polymerization obtained in Examples 1, 6, and 7, 200 particles are uniformly yellow (neutralization index is 0). On the other hand, the particles of the water-absorbent resin powder (E) are mixed with particles that develop in various colors from dark green to red, and the neutralization rate of individual particles is very uneven (neutralization index is 15). That's it).
[0125]
  (ManufacturingExample 6): Production example of water absorbent resin powder (F) / neutralization polymerization
  ManufacturingIn Example 1, the monomer concentration was changed to 39% by weight, the neutralization rate was changed to 71 mol%, and polyethylene glycol diacrylate was changed to 9.6 g.ManufacturingPolymerization, drying and pulverization were carried out in the same manner as in Example 1. The obtained pulverized product was further classified with a JIS standard sieve having openings of 500 μm and 300 μm to obtain a water absorbent resin powder (F) in which most of the particles were in the range of 500 μm to 300 μm. The absorption capacity of the obtained water absorbent resin powder (F) under no pressure was 32 (g / g), and the soluble content was 10% by weight.
  (ManufacturingExample 7): Production example of water-absorbent resin powder (G) / neutralization polymerization
  ManufacturingIn Example 1, the monomer concentration was 41 wt%, the neutralization rate was 71 mol%, polyethylene glycol diacrylate 5.47 g, sodium persulfate aqueous solution 30.8 g, L-ascorbic acid aqueous solution 2.57 g, hot air drying temperature 180 Except for changing to ℃, hot air drying time 50 minutesManufacturingPolymerization, drying and pulverization were carried out in the same manner as in Example 1. The obtained pulverized product was further classified with a JIS standard sieve having an opening of 850 μm to obtain a water-absorbent resin powder (G) in which most of the particles were in the range of 850 μm or less.
[0126]
  The resulting water-absorbent resin powder (G) had an absorption capacity of 38 (g / g) under no pressure, a soluble content of 13% by weight, and a weight average particle size (D50) of 400 μm.
  (Example2): Water-absorbent resin powder (E) has a crosslinking treatment / pH buffering agent
  Manufacturing100 g of the water-absorbent resin powder (E) obtained in Example 5 was added with 0.5 g of ethylene glycol diglycidyl ether (Denacol EX-810, manufactured by Nagase Kasei Co., Ltd.), 1.0 g of propylene glycol, and neutral phosphate pH. After mixing a surface treatment agent composed of 6.0 g of a standard solution (potassium dihydrogen phosphate / disodium hydrogen phosphate; pH 6.86) and 1.0 g of isopropyl alcohol, the mixture was heated at 120 ° C. for 30 minutes. The water-absorbing agent (17) was obtained by processing. The obtained water-absorbing agent (17) was also in the form of a powder. The results of measuring the absorption capacity under no pressure and the absorption capacity under pressure are shown in Table 5.
[0127]
  (Comparative Example 17): Crosslinking treatment of water-absorbent resin powder (E) / no pH buffering agent
  Example2The comparative water-absorbing agent (17) was obtained in the same manner except that 6.0 g of water was used instead of the neutral phosphate pH standard solution. Absorption capacity under no pressure and absorption capacity under pressure were measured, and the results are shown in Table 5.
  (Example3): Water-absorbent resin powder (F) is crosslinked / pH buffered
  ManufacturingMixing 100 g of the water-absorbent resin powder (F) obtained in Example 6 with 0.32 g of 1,4-butanediol, 0.5 g of propylene glycol, 2.73 g of water, and 1.2 g of sodium dihydrogen phosphate dihydrate After mixing the liquid surface treatment agent, the mixture was heat-treated at 197 ° C. for 10 minutes to obtain a water absorbing agent (18). The resultant water-absorbing agent (18) was also in the form of a powder. Table 5 shows the results of measuring the absorption capacity under no pressure and the absorption capacity under pressure.
[0128]
  (Comparative Example 18): Cross-linking treatment of water-absorbent resin powder (F) / no pH buffering agent
  Example3In Comparative Example 1, a comparative water-absorbing agent (18) was obtained in the same manner except that 0.6 g of phosphoric acid (85% by weight) was used instead of sodium dihydrogen phosphate dihydrate. Table 5 shows the results of measuring the absorption capacity under no pressure and the absorption capacity under pressure.
  (Comparative Example 19): Cross-linking treatment of water-absorbent resin powder (F) / no pH buffering agent
  Example3In Comparative Example 1, a comparative water-absorbing agent (19) was obtained in the same manner except that sodium dihydrogen phosphate dihydrate was not used. Table 5 shows the results of measuring the absorption capacity under no pressure and the absorption capacity under pressure.
[0129]
  (Example4): Water-absorbent resin powder (G) cross-linking treatment / with pH buffering agent
  ManufacturingSurface treatment comprising a mixed liquid of 0.32 g of 1,4-butanediol, 0.5 g of propylene glycol, 2.73 g of water, and 0.2 g of sodium hydrogencarbonate on 100 g of the water absorbent resin powder (G) obtained in Example 7. After mixing the agent solution, the mixture was heat-treated at 212 ° C. for 25 minutes to obtain a water absorbing agent (19). Table 5 shows the results of measuring the absorption capacity under no pressure and the absorption capacity under pressure.
  (Example5): Water-absorbent resin powder (G) cross-linking treatment / with pH buffering agent
  ManufacturingSurface treatment comprising a mixed liquid of 0.32 g of 1,4-butanediol, 0.5 g of propylene glycol, 2.73 g of water, and 0.24 g of potassium bicarbonate to 100 g of the water absorbent resin powder (G) obtained in Example 7. After mixing the agent solution, the mixture was heated at 212 ° C. for 25 minutes to obtain a water absorbing agent (20). Table 5 shows the results of measuring the absorption capacity under no pressure and the absorption capacity under pressure.
[0130]
  (Comparative Example 20): Cross-linking treatment of water-absorbent resin powder (G) / no pH buffering agent
  Example4The comparative water-absorbing agent (20) was obtained in the same manner except that sodium bicarbonate was not used. Table 5 shows the results of measuring the absorption capacity under no pressure and the absorption capacity under pressure.
  (referenceExample16): Continuous production system
  71 mol% neutralized acrylic acid partial sodium salt and polyethylene glycol diacrylate (n = 9)ManufacturingIn the ratio of Example 3, aqueous solution polymerization (belt residence time: about 30 minutes, thickness: about 25 mm) was continuously performed, and the obtained water-containing gel-containing crosslinked polymer was roughly crushed into particles with a meat chopper. This was spread thinly on a perforated plate of a band dryer and dried with continuous hot air at 180 ° C. for 30 minutes. A block-shaped dry polymer was obtained at the outlet of the dryer. The dried polymer was taken out and crushed at the same time, and the resulting particulate dried product was continuously supplied to a three-stage roll granulator (roll gap is 1.0 mm / 0.55 mm / 0.42 mm from above) at 1000 kg / h. And then crushed. The obtained particulate water-absorbing resin powder of about 60 ° C. is classified by a sieving device having a sieve screen having a mesh opening of 850 μm, and a water-absorbing resin powder having a size of 90% by weight or more and less than 850 μm and a size of 150 μm or more (H (Average particle size: 430 to 460 μm). The resulting water-absorbent resin powder (H) had an average absorption capacity (CRC) of 40 g / g under no pressure, and the average amount of soluble components was 11% by weight. The physical properties of CRC and soluble content are average values measured every 2 hours (2000 kg / Lot).
[0131]
Further, the water-absorbent resin powder (H) was continuously supplied to a high-speed continuous mixer (turbulator / 1000 rpm) at 1000 kg / h, and further 1,4-butanediol / propylene was added to the water-absorbent resin powder (H). A surface cross-linking agent aqueous solution composed of glycol / water / 24% aqueous sodium hydroxide = 0.384 / 0.63 / 3.39 / 0.3 (weight% / powder) is sprayed into droplets of about 200 μm. Sprayed and mixed. Subsequently, the obtained mixture was continuously heat-treated with a paddle dryer at 195 ° C. for 40 minutes to obtain a water absorbent powder. Furthermore, the obtained water-absorbing agent powder was classified by a sieving device having a sieve screen having a mesh opening of 850 μm to obtain a water-absorbing agent (21) in which particles having a size of less than 850 μm and a size of 150 μm or more were 90% by weight or more.
[0132]
  The series of steps (polymerization, drying, pulverization, heat treatment) was performed continuously for 24 hours, and the physical properties (Lot number: 11 points) of the water-absorbing agent were measured every 2 hours (2000 kg / Lot). The average value of the absorption capacity under pressure was 31.1 g / g, the average value of the absorption capacity under pressure was 25.5 g / g, and the average value of the saline flow conductivity was 30 (SFC value per lot: 32 32, 28, 28, 30, 27, 27, 32, 31, 32, 28), and the standard deviation of the SFC was 2.1.
  (referenceExample17): Continuous production system
  referenceExample16In the above, continuous production was carried out in the same manner except that 24 hours was changed to 10 days to obtain a water absorbing agent (22). As a result of measuring the physical properties (Lot number: 110 points) of the water-absorbing agent every 2 hours (2000 kg / Lot), the average value of the absorption capacity under no pressure was 31.3 g / g, and the average value of the absorption capacity under pressure Was 25.2 g / g, the average value of physiological saline flow inductivity was 30 (the SFC value for each lot was omitted), and the standard deviation value of the SFC was 3.9.
[0133]
  (Comparative Example 21): Continuous production system
  referenceExample16In Example 1, a continuous production was carried out in the same manner except that a 24% aqueous sodium hydroxide solution was not used to obtain a comparative water-absorbing agent (21). As a result of measuring the physical properties (Lot number: 11 points) of the water-absorbing agent every 2 hours (2000 kg / Lot), the average value of the absorption capacity under no pressure was 31.1 g / g, the average value of the absorption capacity under pressure Is 24.2 g / g, the average value of the saline flow inductivity is 20 (SFC values per lot: 26, 17, 11, 17, 17, 18, 20, 17, 16, 28, 28), The standard deviation value of SFC was 5.5.
[0134]
  referenceExample16andreferenceExample17The water-absorbing agent (21), (22) described in (2) has a smaller standard deviation of SFC than the comparative water-absorbing agent (21) described in Comparative Example 21, and the water-absorbing agent of the present invention is continuously produced. This indicates that there is no occurrence of defective products (such as low SFC products) and that variations in quality (SFC) are reduced.
[0135]
[Table 1]

[0136]
[Table 2]

[0137]
[Table 3]

[0138]
  referenceExample 1 andreferenceThe water-absorbing agents (1) and (2) described in Example 2 have a higher absorption capacity under pressure than the comparative surface-crosslinked water-absorbing agents (1) and (2). Excellent balance of reduction absorption.
  referenceExample3The water-absorbing agent (3) described in 1 is superior to the comparative water-absorbing agent (3) described in Comparative Example 3 in three balances of absorption capacity under no pressure, absorption capacity under pressure, and saline flow conductivity. ing.
  further,referenceExample 4 andreferenceExample 5 andreferenceThe water-absorbing agent (4), (5), (6) described in Example 6 has substantially the same absorption capacity without pressure as the comparative water-absorbing agent (4) described in Comparative Example 4, but is physiological saline. Water flow inductivity shows a high value.
[0139]
  Similarly,referenceExample 7 andreferenceExample 8 andreferenceIn the water-absorbing agents (7), (8) and (9) described in Example 9, the water-absorbing agent (5) and the comparative water-absorbing agent (6) described in Comparative Example 5 and Comparative Example 6 were not added. The absorption ratio under reduction is almost the same, but the absorption ratio under pressure and saline flow inductivity are high.
  Also,referenceExample 10,referenceExample 11, Example1The water-absorbing agents (10), (11), and (12) described in 1 are compared with the comparative water-absorbing agents (7), (8), and (9) described in Comparative Example 7, Comparative Example 8, and Comparative Example 9, respectively. The absorption capacity under no pressure is almost the same, but the saline flow inductivity shows a high value.
[0140]
  referenceExample12andreferenceExample13The water-absorbing agents (13) and (14) described in 1 were compared with the comparative water-absorbing agents (10), (11), and (12) described in Comparative Example 10, Comparative Example 11 and Comparative Example 12, respectively. The SFC variation coefficient is small, the SFC variation rate is large, and the variation in SFC is reduced in both cases.
  Also,referenceExample14andreferenceExample15In the water absorbing agents (15) and (16) described in 1), the SFC change index and the SFC fluctuation index are small, the SFC fluctuation rate is large, and both of the variations in SFC are reduced.
  Thus, the water-absorbing agent produced by the method of the present invention is excellent in three balances of absorption capacity under no pressure, absorption capacity under pressure, and physiological saline flow inductivity, and has good performance. Furthermore, since there is little variation in SFC for each particle size, it is a very excellent water-absorbing agent in stabilizing the performance of diapers.
[0141]
[Table 4]

[0142]
The comparative water-absorbing agents (13), (14), (15), and (16) described in Comparative Example 13, Comparative Example 14, Comparative Example 15, and Comparative Example 16 are all absorbed under no pressure and absorbed under pressure. The balance between magnification and physiological saline flow inductivity was poor.
[0143]
[Table 5]

[0144]
  Example2The water-absorbing agent (17) described is superior to the comparative water-absorbing agent (17) described in Comparative Example 17 in terms of the balance between the absorption capacity without pressure and the absorption capacity under pressure and the total thereof.
  Examples3The water-absorbing agent (18) described above undergoes a cross-linking reaction in a short time of 10 minutes as compared with the comparative water-absorbing agent (18) described in Comparative Example 18 to which phosphoric acid has been added. Although it is the same, the absorption capacity under pressure shows a high value. Furthermore, for the comparative water-absorbing agent (19) described in Comparative Example 19 in which nothing was added, sufficient crosslinking reaction did not proceed in a short time of 10 minutes, and almost no decrease in absorption capacity under no pressure was observed. Absorption capacity under pressure is also low.
[0145]
Thus, the water-absorbing agent produced by the method of the present invention is excellent in the balance between the absorption capacity under no pressure and the absorption capacity under pressure and the total thereof, and has good performance even in a short reaction time.
[0146]
【The invention's effect】
According to the present invention, during the crosslinking treatment, while exhibiting the effect as a mixing aid, it does not inhibit the crosslinking reaction, and in some cases also has an effect as a reaction catalyst, and in the partially neutralized water-absorbing resin. Uniform surface cross-linking can be realized almost regardless of the difference in the sum rate and the uniformity of the neutralization rate resulting from the post-neutralization operation of the acid type polymerization. Absorption capacity under no pressure, Absorption capacity under pressure, Saline flow A method for producing a water-absorbing agent having a stable physical property in a short time with excellent balance of inductivity and small fluctuation (variation) of physiological saline flow-inductive value in each lot during production or in each lot, and A water absorbing agent can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a measuring apparatus used for measurement of physiological saline flow inductivity.
FIG. 2 is a schematic side view (a) and a schematic plan view (b) of a glass container used for a mechanical damage test.
FIG. 3 is a schematic view of a disperser used for a mechanical damage test.
[Explanation of symbols]
31 tanks
32 glass tubes
33 0.69 wt% sodium chloride aqueous solution
34 L-shaped tube with cock
35 cock
40 containers
41 cells
42 Stainless steel wire mesh
43 Stainless steel wire mesh
44 swelling gel
45 Glass filter
46 piston
47 Hole in piston
48 Collection container
49 Precision Balance
51 glass container
52 Disperser
53 Upper clamp
54 Lower clamp

Claims (11)

A method for producing a water-absorbing agent comprising mixing a water-absorbing resin powder (a) containing an acid group with a surface cross-linking agent (c) capable of reacting with the acid group, and crosslinking the water-absorbing resin powder (a).
The water-absorbent resin powder has a weight average particle diameter (D50) based on the following definition of 300 to 600 μm and a fine powder of 150 μm or less in an amount of 10% by weight or less. The amount is 0.005-0.5 mol%), and
When mixing the surface cross-linking agent , a non-reducing alkali metal salt pH buffer (b2) which is a partial alkali metal salt of an inorganic polybasic acid or a partial alkali metal salt of an organic polyvalent carboxylic acid is also mixed.
A method for producing a water-absorbing agent.
However, the weight average particle diameter (D50) of the water-absorbent resin powder is sieved with a JIS standard sieve (850 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, 75 μm), and the residual percentage R is logarithmic probability paper. It is specified by plotting. The method for producing a water-absorbing agent according to claim 1 , wherein the alkali metal salt pH buffer (b2) comprises one or more of hydrogen carbonate, dihydrogen phosphate, and hydrogen phosphate. . The method for producing a water-absorbing agent according to claim 1 or 2 , wherein the surface crosslinking agent (c) is a dehydration-reactive crosslinking agent (c1). The method for producing a water-absorbing agent according to claim 3 , wherein a non-dehydrating reactive crosslinking agent is also used as the surface crosslinking agent together with the dehydrating reactive crosslinking agent (c1) when the surface crosslinking agent is mixed. The method for producing a water absorbing agent according to claim 3 or 4 , wherein the dehydration-reactive crosslinking agent (c1) is a polyhydric alcohol compound. After the aqueous solution was mixed before Kihi reducing alkali metal salt pH buffer agent (b2) in advance to the surface cross-linking agent (c) or dehydration reactive crosslinking agent (c1), the aqueous solution, the water-absorbent resin The method for producing a water-absorbing agent according to any one of claims 1 to 5 , wherein the powder (a) or (a1) is added by spraying. The manufacturing method according to any one of claims 1 to 6 , wherein 0.5 to 20 parts by weight of water is used at a ratio of 100 parts by weight of the water-absorbing resin when the surface crosslinking agent is mixed. The manufacturing method according to any one of claims 1 to 7 , wherein 0 to 10 parts by weight of a hydrophilic organic solvent is used in a ratio with respect to 100 parts by weight of the water-absorbing resin when the surface crosslinking agent is mixed. The manufacturing method of the water absorbing agent in any one of Claim 1-8 whose temperature of the water absorbing resin powder before mixing a surface crosslinking agent is 40-70 degreeC. The method for producing a water absorbing agent according to any one of claims 1 to 9 , wherein the crosslinking treatment is performed by a heat treatment at 150 to 230 ° C. The water-absorbent resin, polymerizing a monomer composed mainly of acrylic acid and / or its salts, obtained by post-neutralization Furthermore, a polyacrylate crosslinked polymer, Claims 1 to 10 The manufacturing method of the water absorbing agent in any one of.

Images