JP4286335B2 - Method for producing water absorbent resin - Google Patents

Description

（式中、Ｘ₁ 、Ｘ₂ は、それぞれ独立して、炭素数１〜４のアルキレン基を表し、Ｒ₁、Ｒ₂ 、Ｒ₃ 、Ｒ₄ 、Ｒ₅ 、Ｒ₆ は、それぞれ独立して、水素原子、炭素数１〜４のアルキル基、アリール基、アリル基、またはベンジル基を表す）または一般式（２）
【００３７】
【化２】

（式中、Ｘ₃ 、Ｘ₄ は、それぞれ独立して、炭素数１〜４のアルキレン基を表し、Ｘ₅、Ｘ₆ は、それぞれ独立して、炭素数２〜４のアルキレン基を表し、Ｒ₇ 、Ｒ₈ は、それぞれ独立して、水素原子または炭素数１〜４のアルキル基を表す）
で表される、アミノ基含有アゾ化合物のアクリル酸塩；等が挙げられる。これら発泡剤は、単独で用いてもよく、また、二種類以上を併用してもよい。炭酸ナトリウム等の炭酸塩を用いる場合、界面活性剤や分散剤を用いることが好ましい。界面活性剤や分散剤を用いることで、得られる含水ゲルの気泡の平均気泡径が大きくなり過ぎて、吸収速度が遅くなることを防ぐことができる。
【００３８】
上記例示の発泡剤のうち、アミノ基含有アゾ化合物のアクリル酸塩がより好ましい。アミノ基含有アゾ化合物のアクリル酸塩は、界面活性剤や水溶性高分子等の分散安定剤を用いなくても、或いは、単量体水溶液を攪拌しなくても、その平均粒子径を所定の値に維持したまま、該単量体水溶液中に静置状態で均一に分散させることができ、沈降や浮遊、分離を引き起こすことはない。そして、アミノ基含有アゾ化合物のアクリル酸塩は、アクリル酸塩系単量体に対する分散性に特に優れている。
【００３９】
上記一般式（１）または一般式（２）で表されるアミノ基含有アゾ化合物のアクリル酸塩としては、具体的には、例えば、２，２’−アゾビス（２−メチル−Ｎ−フェニルプロピオンアミジン）二アクリル酸塩、２，２’−アゾビス［Ｎ−（４−クロロフェニル）−２−メチル−プロピオンアミジン］二アクリル酸塩、２，２’−アゾビス［Ｎ−（４−ヒドロキシフェニル）−２−メチルプロピオンアミジン］二アクリル酸塩、２，２’−アゾビス［２−メチル−Ｎ−（フェニルメチル）−プロピオンアミジン］二アクリル酸塩、２，２’−アゾビス［２−メチル−Ｎ−（２−プロペニル）プロピオンアミジン］二アクリル酸塩、２，２’−アゾビス（２−メチルプロピオンアミジン）二アクリル酸塩、２，２’−アゾビス［Ｎ−（２−ヒドロキシエチル）−２−メチル−プロピオンアミジン］二アクリル酸塩、２，２’−アゾビス［２−（５−メチル−２−イミダゾリン−２−イル）プロパン］二アクリル酸塩、２，２’−アゾビス［２−（２−イミダゾリン−２−イル）プロパン］二アクリル酸塩、２，２’−アゾビス−［２−（４，５，６，７−テトラヒドロ−１Ｈ−１，３−ジアゼピン−２−イル）プロパン］二アクリル酸塩、２，２’−アゾビス［２−（３，４，５，６−テトラヒドロピリミジン−２−イル）プロパン］二アクリル酸塩、２，２’−アゾビス［２−（５−ヒドロキシ−３，４，５，６−テトラヒドロピリミジン−２−イル）プロパン］二アクリル酸塩、２，２’−アゾビス｛２−［１−（２−ヒドロキシエチル）−２−イミダゾリン−２−イル］プロパン｝二アクリル酸塩等が挙げられるが、特に限定されるものではない。
【００４０】
尚、アミノ基含有アゾ化合物のアクリル酸塩は、例えば単量体水溶液中で析出させた後、ろ過等の方法を用いることにより、単離することができる。また、アミノ基含有アゾ化合物のアクリル酸塩を単量体水溶液中で析出させる際には、該単量体水溶液に、必要に応じて、冷却等を行ってもよい。
【００４１】
上記の発泡剤は、予め調製したものを単量体水溶液に添加して使用してもよく、また、該発泡剤の前駆体（以下、発泡剤前駆体と称する）を単量体水溶液に溶解した後、必要に応じて、該単量体水溶液に炭酸ガスやアクリル酸塩を添加することにより、単量体水溶液中で調製することもできる。つまり、発泡剤前駆体と、炭酸ガスやアクリル酸塩とを単量体水溶液中で反応させることにより、発泡剤を析出させることもできる。該アクリル酸塩としてはアクリル酸ナトリウムが好適である。また、単量体がアクリル酸塩系単量体である場合には、該単量体をアクリル酸塩として作用させることができる。
【００４２】
上記アミノ基含有アゾ化合物のアクリル酸塩は、発泡剤としての機能と、ラジカル重合開始剤としての機能とを備えている。そして、該アミノ基含有アゾ化合物のアクリル酸塩の存在下に単量体を重合させることにより、水可溶性成分量並びに残存単量体量がさらに一層低減された吸水性樹脂を得ることができる。つまり、アミノ基含有アゾ化合物のアクリル酸塩を用いることにより、水可溶性成分量が２０重量％以下であり、かつ、残存単量体量が１，０００ｐｐｍ以下に低減された吸水性樹脂を得ることができる。
【００４３】
単量体に対する上記発泡剤の使用量は、単量体および発泡剤の組み合わせ等に応じて設定すればよく、特に限定されるものではないが、単量体１００重量部に対して０．００１重量部〜１０重量部の範囲内がより好ましい。発泡剤の使用量が上記の範囲外である場合には、得られる吸水性樹脂の吸水特性が不充分となるおそれがある。
【００４４】
また、単量体水溶液中において重合時に分散状態で存在する発泡剤の平均粒子径は、１μｍ〜５００μｍの範囲内が好ましい。発泡剤の平均粒子径を上記の範囲内に設定することにより、吸水性樹脂の平均孔径を１０μｍ〜１，０００μｍの範囲内に調整することができ、該吸水性樹脂の吸水特性（例えば、水性液体の拡散性や吸水速度等）を向上させることができる。つまり、発泡剤の平均粒子径を設定することにより、吸水性樹脂の平均孔径を所望の範囲内に設定することができる。
【００４５】
発泡剤の平均粒子径が１μｍよりも小さい場合、発泡が不充分となり、吸水性樹脂の平均孔径を所望の範囲内に調整することができないので好ましくない。一方、発泡剤の平均粒子径が５００μｍよりも大きい場合には、吸水性樹脂の平均孔径を所望の範囲内に調整することができない。また、得られる吸水性樹脂のゲル強度が低下すると共に、水可溶性成分量が増加するので好ましくない。尚、単量体水溶液中における発泡剤の平均粒子径は、レーザー式粒度分布計を用いることによって容易に測定することができる。
【００４６】
上記発泡剤が無機化合物である場合の発泡剤前駆体としては、具体的には、例えば、酸化カルシウムや酸化マグネシウム等が挙げられる。
【００４７】
上記発泡剤がアミノ基含有アゾ化合物のアクリル酸塩である場合の発泡剤前駆体は、アミノ基含有アゾ化合物の塩酸塩であり、具体的には、例えば、２，２’−アゾビス（２−メチル−Ｎ−フェニルプロピオンアミジン）二塩酸塩、２，２’−アゾビス［Ｎ−（４−クロロフェニル）−２−メチル−プロピオンアミジン］二塩酸塩、２，２’−アゾビス［Ｎ−（４−ヒドロキシフェニル）−２−メチルプロピオンアミジン］二塩酸塩、２，２’−アゾビス［２−メチル−Ｎ−（フェニルメチル）−プロピオンアミジン］二塩酸塩、２，２’−アゾビス［２−メチル−Ｎ−（２−プロペニル）プロピオンアミジン］二塩酸塩、２，２’−アゾビス（２−メチルプロピオンアミジン）二塩酸塩、２，２’−アゾビス［Ｎ−（２−ヒドロキシエチル）−２−メチル−プロピオンアミジン］二塩酸塩、２，２’−アゾビス［２−（５−メチル−２−イミダゾリン−２−イル）プロパン］二塩酸塩、２，２’−アゾビス［２−（２−イミダゾリン−２−イル）プロパン］二塩酸塩、２，２’−アゾビス−［２−（４，５，６，７−テトラヒドロ−１Ｈ−１，３−ジアゼピン−２−イル）プロパン］二塩酸塩、２，２’−アゾビス［２−（３，４，５，６−テトラヒドロピリミジン−２−イル）プロパン］二塩酸塩、２，２’−アゾビス［２−（５−ヒドロキシ−３，４，５，６−テトラヒドロピリミジン−２−イル）プロパン］二塩酸塩、２，２’−アゾビス｛２−［１−（２−ヒドロキシエチル）−２−イミダゾリン−２−イル］プロパン｝二塩酸塩等が挙げられる。これらアミノ基含有アゾ化合物の塩酸塩は、熱分解型アゾ系重合開始剤である。
【００４８】
アミノ基含有アゾ化合物の塩酸塩とアクリル酸塩とを反応させてアミノ基含有アゾ化合物のアクリル酸塩を調製する際の条件は、特に限定されるものではないが、以下の条件が好ましい。そして、これら条件を任意に設定して、アミノ基含有アゾ化合物のアクリル酸塩の分散時における粒子径を適宜調節することにより、得られる吸水性樹脂の孔径を所望の大きさに調節すればよい。
【００４９】
即ち、調製温度は、−１０℃〜５０℃が好ましく、０℃〜４０℃がより好ましい。また、アクリル酸塩は、アクリル酸アルカリ金属塩がより好ましく、アクリル酸ナトリウムがさらに好ましい。該アクリル酸塩の中和率は、５０モル％以上が好ましく、７０モル％以上がより好ましい。そして、単量体水溶液中におけるアクリル酸塩の濃度は、２０重量％〜飽和濃度の範囲内が好ましく、２５重量％〜飽和濃度の範囲内がより好ましい。
【００５０】
また、アミノ基含有アゾ化合物のアクリル酸塩を調製する際には、単量体水溶液を攪拌することが好ましい。そして、単量体水溶液を好ましくは１０ｒｐｍ以上、より好ましくは２０ｒｐｍ〜１０，０００ｒｐｍの範囲内で攪拌することにより、ほぼ均一な粒子径を有するアミノ基含有アゾ化合物のアクリル酸塩を短時間で調製することができる。尚、調製されたアミノ基含有アゾ化合物のアクリル酸塩は、単量体の重合にそのまま用いればよく、一旦単離する必要はない。
【００５１】
アミノ基含有アゾ化合物のアクリル酸塩を単量体水溶液中で調製する方法、つまり、単量体水溶液に該アミノ基含有アゾ化合物のアクリル酸塩を分散させる方法としては、例えば、以下の方法が挙げられる。即ち、中和率が１００％のアクリル酸塩にアミノ基含有アゾ化合物の塩酸塩を添加してアミノ基含有アゾ化合物のアクリル酸塩を調製した後、該アクリル酸塩に未中和のアクリル酸等の単量体、架橋剤、および、必要に応じて溶媒を混合して、単量体水溶液を得る方法；予め調製された単量体水溶液に、アミノ基含有アゾ化合物の塩酸塩、および、必要に応じてアクリル酸塩を添加して、アミノ基含有アゾ化合物のアクリル酸塩が分散した単量体水溶液を調製する方法等が挙げられる。これら方法のうち、後者の方法が、アミノ基含有アゾ化合物のアクリル酸塩をより効率的に得ることができ、かつ、その粒子径がより均一となるので好ましい。尚、アミノ基含有アゾ化合物のアクリル酸塩を調製した後、単量体水溶液に水等の溶媒を添加することにより、該単量体水溶液中の単量体を所望の濃度に調節してもよい。
【００５２】
内部に気泡を含有する含水ゲルは、上記単量体水溶液に窒素、二酸化炭素、アルゴン、ヘリウム、空気等の、重合反応に対し不活性となる不活性ガスの気体を分散させた状態で該単量体を重合することにより得ることもできる。分散した不活性ガスの気体は、単量体の重合を阻害する恐れがないので、吸水性能に優れた吸水性樹脂を得ることができる。また、後述する界面活性剤等を併用することにより、内部に分散した気泡の大きさや分布を調整することが容易で、所望の吸水性樹脂を得ることができる。
【００５３】
不活性ガスの気泡を単量体水溶液中に分散させる方法としては、上記単量体水溶液中に不活性ガスを導入する方法、単量体水溶液を高速で強く攪拌する方法、発泡剤を予め添加する方法等が挙げられる。また、これらの方法を組み合わせて、不活性ガスの気泡を単量体水溶液中に分散させてもよい。上記高速で強く攪拌する方法としては、スターラーおよび攪拌羽により強攪拌する方法、高速ホモジナイザーおよび超音波ホモジナイザーにより強攪拌する方法等が挙げられる。
【００５４】
上記不活性ガスの気泡が分散した単量体水溶液の体積は、非分散状態の単量体水溶液の体積に対して１．０２倍以上であることが好ましく、１．０８倍以上であることがより好ましく、１．１１倍以上であることがさらに好ましく、１．２倍以上であることが特に好ましい。
【００５５】
従来より行われてきた攪拌下における重合反応操作においても、単量体水溶液に気泡が混入することもあり得るが、発明者らの確認によれば、通常の操作で気泡が混入しても、それによる体積変化は１．０１倍にも満たない。不活性ガスの気泡が分散した単量体水溶液の体積が非分散状態の単量体水溶液の体積に対して１．０２倍以上の体積変化を示すのは、上記方法により意図的に含水ゲルに気泡を含有させた結果であり、これにより、吸水性能のより一層向上した吸水性樹脂を得ることができる。尚、単量体水溶液に不活性ガスの気泡が分散した状態は、単量体水溶液の透明性が低下することにより、容易に目視で確認できる。さらに、単量体水溶液の体積変化は、反応容器中の喫水線の高さだけの変化により現れるので、体積変化は容易に確認できる。
【００５６】
上記不活性ガスからなる気泡を単量体水溶液に分散させる際には、界面活性剤を併用することが好ましい。界面活性剤を併用することにより、上記該気泡を安定に分散させることができる。また、気泡の気泡径および気泡の分布は、上記界面活性剤によって、より容易に制御することが可能である。
【００５７】
上記の界面活性剤としては、アニオン系界面活性剤、ノニオン系界面活性剤、カチオン系界面活性剤、および、両性イオン界面活性剤等が挙げられる。アニオン系界面活性剤としては、具体的には、例えば、混合脂肪酸ナトリウム石鹸、半硬化牛脂肪酸ナトリウム石鹸、ステアリン酸ナトリウム石鹸、オレイン酸カリウム石鹸、オレイン酸ナトリウム石鹸、ヒマシ油カリウム石鹸等の脂肪酸塩；ラウリル硫酸ナトリウム、ラウリル硫酸アンモニウム、高級アルコール硫酸ナトリウム、ラウリル硫酸トリエタノールアミン等のアルキル硫酸エステル塩；ドデシルベンゼンスルホン酸ナトリウム等のアルキルベンゼンスルホン酸塩；アルキルナフタレンスルホン酸ナトリウム等のアルキルナフタレンスルホン酸塩；ジアルキルスルホコハク酸ナトリウム等のアルキルスルホコハク酸塩；アルキルジフェニルエーテルジスルホン酸ナトリウム等のアルキルジフェニルエーテルジスルホン酸塩；アルキルリン酸カリウム等のアルキルリン酸塩；ポリオキシエチレンラウリルエーテル硫酸ナトリウム、ポリオキシエチレンアルキルエーテル硫酸ナトリウム、ポリオキシエチレンアルキルエーテル硫酸トリエタノールアミン、ポリオキシエチレンアルキルフェニルエーテル硫酸ナトリウム等のポリオキシエチレンアルキル（またはアルキルアリル）硫酸エステル塩；特殊反応型アニオン界面活性剤；特殊カルボン酸型界面活性剤；β−ナフタレンスルホン酸ホルマリン縮合物のナトリウム塩、特殊芳香族スルホン酸ホルマリン縮合物のナトリウム塩等のナフタレンスルホン酸ホルマリン縮合物；特殊ポリカルボン酸型高分子界面活性剤；ポリオキシエチレンアルキルリン酸エステル等が挙げられるが、特に限定されるものではない。
【００５８】
ノニオン系界面活性剤としては、具体的には、例えば、ポリオキシエチレンラウリルエーテル、ポリオキシエチレンセチルエーテル、ポリオキシエチレンステアリルエーテル、ポリオキシエチレンオレイルエーテル、ポリオキシエチレン高級アルコールエーテル等のポリオキシエチレンアルキルエーテル、ポリオキシエチレンノニルフェニルエーテル等のポリオキシエチレンアルキルアリールエーテル；ポリオキシエチレン誘導体；ソルビタンモノラウレート、ソルビタンモノパルミテート、ソルビタンモノステアレート、ソルビタントリステアレート、ソルビタンモノオレエート、ソルビタントリオレエート、ソルビタンセスキオレエート、ソルビタンジステアレート等のソルビタン脂肪酸エステル；ポリオキシエチレンソルビタンモノラウレート、ポリオキシエチレンソルビタンモノパルミテート、ポリオキシエチレンソルビタンモノステアレート、ポリオキシエチレンソルビタントリステアレート、ポリオキシエチレンソルビタンモノオレエート、ポリオキシエチレンソルビタントリオレエート等のポリオキシエチレンソルビタン脂肪酸エステル；テトラオレイン酸ポリオキシエチレンソルビット等のポリオキシエチレンソルビトール脂肪酸エステル；グリセロールモノステアレート、グリセロールモノオレエート、自己乳化型グリロセールモノステアレート等のグリセリン脂肪酸エステル；ポリエチレングリコールモノラウレート、ポリエチレングリコールモノステアレート、ポリエチレングリコールジステアレート、ポリエチレングリコールモノオレエート等のポリオキシエチレン脂肪酸エステル；ポリオキシエチレンアルキルアミン；ポリオキシエチレン硬化ヒマシ油；アルキルアルカノールアミド等が挙げられるが、特に限定されるものではない。
【００５９】
カチオン系界面活性剤および両面界面活性剤としては、具体的には、例えば、ココナットアミンアセテート、ステアリルアミンアセテート等のアルキルアミン塩；ラウリルトリメチルアンモニウムクロライド、ステアリルトリメチルアンモニウムクロライド、セチルトリメチルアンモニウムクロライド、ジステアリルジメチルアンモニウムクロライド、アルキルベンジルジメチルアンモニウムクロライド等の第四級アンモニウム塩；ラウリルベタイン、ステアリルベタイン、ラウリルカルボキシメチルヒドロキシエチルイミダゾリニウムベタイン等のアルキルベタイン；ラウリルジメチルアミンオキサイド等のアミンオキサイド；等が挙げられるが、特に限定されるものではない。
【００６０】
さらに、界面活性剤としては、フッ素系界面活性剤がある。フッ素系界面活性剤を用いることにより、単量体水溶液中に不活性ガスの気泡を長時間安定に分散させることができる。また、気泡の量、気泡の気泡径の制御も容易である。そして、得られる吸水性樹脂は発泡体で、多孔質なものとなり、吸水速度の速いものとなる。本発明において使用されるフッ素系界面活性剤としては、特に限定されるものではなく、従来公知の種々のものがあるが、例えば、一般の界面活性剤の親油基の水素をフッ素に置換してパーフルオロアルキル基としたものであり、界面活性が格段に強くなっているものが好適である。
【００６１】
フッ素系界面活性剤の親水基を変えると、アニオン型、ノニオン型、カチオン型および両性型の４種類があるが、疏水基の場合、同じ構造のフルオロカーボン鎖を用いることが多い。また、疏水基である炭素鎖は直鎖であっても分枝状であってもよい。上記フッ素系界面活性剤としては、具体的には、例えば、フルオロアルキル（Ｃ₂ 〜Ｃ₁₀）カルボン酸、Ｎ−パーフルオロオクチルスルホニルグルタミン酸ジナトリウム、３−〔フルオロアルキル（Ｃ₆〜Ｃ₁₁）オキシ〕−１−アルキル（Ｃ₃ 〜Ｃ₄ ）スルホン酸ナトリウム、３−〔ω−フルオロアルカノイル（Ｃ₆〜Ｃ₈ ）−Ｎ−エチルアミノ〕−１−プロパンスルホン酸ナトリウム、Ｎ−〔３−（パーフルオロオクチルスルホンアミド）プロピル〕−Ｎ，Ｎ’−ジメチル−Ｎ−カルボキシメチレンアンモニウムベタイン、フルオロアルキル（Ｃ₁₁〜Ｃ₂₀）カルボン酸、パーフルオロアルキルカルボン酸（Ｃ₇〜Ｃ₁₃）、パーフルオロオクチルスルホン酸ジエタノールアミド、パーフルオロアルキル（Ｃ₄〜Ｃ₁₂）スルホン酸塩（Ｌｉ、Ｋ、Ｎａ）、Ｎ−プロピル−Ｎ−（２−ヒドロキシエチル）パーフルオロオクチルスルホンアミド、パーフルオロアルキル（Ｃ₆〜Ｃ₁₀）スルホンアミドプロピルトリメチルアンモニウム塩、パーフルオロアルキル（Ｃ₆〜Ｃ₁₀）−Ｎ−エチルスルホニルグリシン塩（Ｋ）、リン酸ビス（Ｎ−パーフルオロオクチルスルホニル−Ｎ−エチルアミノエチル）、モノパーフルオロアルキル（Ｃ₆〜Ｃ₁₆）エチルリン酸エステル、パーフルオロアルキル第四級アンモニウムヨウ化物（商品名；フロラードＦＣ−１３５、住友スリーエム株式会社製、カチオン性フッ素系界面活性剤）、パーフルオロアルキルアルコキシレート（商品名；フロラードＦＣ−１７１、住友スリーエム株式会社製、ノニオン性フッ素系界面活性剤）、パーフルオロアルキルスルホン酸カリウム塩（商品名；フロラードＦＣ−９５およびフロラードＦＣ−９８、住友スリーエム株式会社製、アニオン性フッ素系界面活性剤）等が挙げられるが、特に限定されるものではない。これら界面活性剤は、単独で用いてもよく、また、二種類以上を併用してもよい。
【００６２】
これらの界面活性剤の使用量は、水溶性不飽和単量体および水溶性架橋性単量体の合計量１００重量部当たり０．０００１重量部〜１０重量部の範囲内であることが好ましく、０．０００３重量部〜５重量部の範囲内であることがより好ましい。界面活性剤の使用量が０．０００１重量部よりも小さい場合、吸水速度をより充分に向上させることができない場合があるので好ましくない。一方、１０重量部を超えると、その添加量に見合っただけの効果がでなくなることがあり、非経済的であるので好ましくない。
【００６３】
従来から、水溶液重合において界面活性剤を用いることは公知であるが、このような公知技術では吸水速度が全く改善されない。
【００６４】
単量体成分を重合する重合方法は、特に限定されるものではなく、バルク重合、沈澱重合、水溶液重合または逆相懸濁重合等の従来公知の種々の重合方法を採用することができるが、得られる吸水性樹脂の吸水特性を向上させると共に、重合の制御の容易さから、単量体成分を水溶液として、水溶液重合または逆相懸濁重合を行う方が好ましい。
【００６５】
上記の水溶液重合法としては、駆動ベルト上で薄膜状に重合する薄膜重合；所定の型枠の中に単量体成分の水溶液を入れて重合させる方法；所定の形状を有する攪拌翼を備えたニーダー等の混合機を重合装置として用いて単量体成分の水溶液を重合させると共に、生成する含水ゲルを該攪拌翼の剪断力で細分化する重合方法；等が挙げられる。
【００６６】
これら重合方法のうち、後者の重合方法が、重合反応が終了した時点で粒子状の含水ゲルが得られるのでより好ましい。また、重合反応中に単量体を攪拌することなく、静置して重合させる方が好ましい。さらに、上記のエチレン性不飽和の単量体を水溶液重合させる際には、連続式重合、または回分重合のいずれかの方式を採用してもよく、また、常圧、減圧、加圧の何れの圧力下で実施してもよい。尚、重合反応は、窒素、ヘリウム、アルゴン、二酸化炭素等の不活性ガスの気流下で行うことが好ましい。
【００６７】
また、上記の逆相懸濁重合法としては、例えば、単量体成分の水溶液を分散剤の存在下で疎水性有機溶媒に懸濁させて重合させる方法等が挙げられる。逆相懸濁重合法を採用することにより、重合反応が終了した時点で球状（粒子状）の含水ゲルが得られる。
【００６８】
含水ゲルを解砕する方法としては、筒状の解砕室内に、固定刃と、回転する回転刃とを備えた回転式解砕機を使用して固定刃と回転刃との剪断によって解砕を行うことが挙げられる。上記回転式解砕機では、回転刃は、その刃が垂直方向に延びて、固定刃の刃に対し実質的に平行となっており、また、回転刃の回転軸も垂直となっている。上記回転式解砕機では、固定刃は解砕室内の内壁に周方向に沿って１〜４本設けられている一方、回転刃は回転軸から互いに等間隔で、径方向外向きに延びるように、２〜５本設けられている。
【００６９】
上記回転式解砕機では、各回転刃の間に投入された含水ゲルは、回転する回転刃による遠心力により、含水ゲルが自重で、回転刃の径方向外向きに固定刃と回転刃との間に押し出される。このように押し出された含水ゲルは固定刃と回転刃との剪断により切断されて解砕される。これにより、上記回転式解砕機では、遠心力によって、含水ゲル全体に対し、ほぼ均一に力が加えられて、径方向外向きに移動するため、従来のように、押圧されたり、押し出されたりするときに、気泡が押し潰されることが軽減される。このことから、含水ゲル中に含まれる気泡の減少を抑制しながら、すなわち、解砕後の含水ゲルにおける気泡が２０％以上保持されるように上記含水ゲルを解砕することができる。また、上記含水ゲルは、架橋構造を有しているので、従来における水溶性重合ゲルより大きな所定の硬度や粘度を有しており、回転式解砕機内や、固定刃および回転刃に付着することが防止されるため、回転式解砕機により容易に解砕されるものとなる。
【００７０】
解砕時間、すなわち含水ゲルが回転式解砕機に滞留する滞留時間は、含水ゲルの投入量、固定刃および回転刃の刃の大きさ、回転刃の回転速度、または解砕後の含水ゲルの大きさにより適宜設定できるが、１秒間以上３分間未満が好ましく、５秒間以上１分間未満がより好ましい。解砕時間が１秒間より短い場合、含水ゲルの解砕は不十分なものとなり好ましくない。また、解砕時間が３分間以上である場合、含水ゲルが内部に有する気泡が練り潰されたり、解砕後の含水ゲルが細かくなり過ぎるので好ましくない。
【００７１】
解砕後の含水ゲルの粒子径の大きさは、その内部まで乾燥工程によって十分に乾燥できる程度であればよく、０．１ｍｍ〜３０ｍｍの範囲内が好ましく、１ｍｍ〜１５ｍｍの範囲内がより好ましい。解砕後の含水ゲルの粒子径の大きさが０．１ｍｍよりも小さい場合、吸水性樹脂を乾燥中に目詰まりが起こりやすく、乾燥効率が低下し、また、内部の気泡が潰れてしまうので好ましくない。一方、解砕後の含水ゲルの粒子径の大きさが３０ｍｍよりも大きい場合、吸水性樹脂を内部まで十分に乾燥させることが困難となるので、好ましくない。尚、水溶液重合法により得られる含水ゲルが塊状である場合には、該含水ゲルを所定の粒子径を有する粒子状に解砕することがより好ましい。
【００７２】
解砕された含水ゲルは、回転式解砕機のロストルから排出される。ロストルの口径は、一般に１ｍｍ〜５０ｍｍの範囲内であるので、解砕された含水ゲルは、架橋により、粘着性が低下していて減圧下で吸引することにより、該含水ゲルをロストルに詰まることなく排出することができる。
【００７３】
また、このような回転式解砕機を用いて含水ゲルを解砕することにより、従来のミートチョッパーのような押圧やスクリューにより含水ゲルを移動させることがなく、遠心力により固定刃と回転刃との間に含水ゲルが移動するため、押圧や混錬による含水ゲルの気泡の減少が抑制される。また、固定刃と回転する回転刃との間にはさまれた含水ゲルが、固定刃と回転刃とによる剪断により切断されるため、含水ゲルの全体に対する押圧力を低減できて、押圧により気泡が押しつぶされることが軽減できる。これにより、含水ゲルが内部に含有する気泡が２０％以上保持されるので、得られる吸水性樹脂の吸水特性は、より一層向上したものとなる。
【００７４】
また、従来、ミートチョッパー等のスクリュー型押出機；（機械）加圧ニーダー、インターナショナルミキサー、バンバリーミキサー等のニーダー等により、例えば含水ゲルを解砕した場合と比べて、ハサミ等の手作業でしか実現できなかった気泡保持率の高い多孔質な吸水性樹脂を得ることができる。
【００７５】
本願発明の方法では、固定刃と回転刃とを用いて、含水ゲルを連続的に効率よく解砕できるため、従来のようにハサミを用い、手で解砕した場合と比べて、解砕効率をより向上でき、生産性を改善することが可能となる。
【００７６】
さらに、表面架橋剤を添加することにより、吸水性樹脂に二次架橋（表面架橋）を導入してもよい。上記の表面架橋剤は、複数の反応性基を有し、吸水性樹脂が有するカルボキシル基等の官能基と反応する化合物であればよく、一般に該用途に用いられる公知の表面架橋剤を採用することができる。
【００７７】
上記の表面架橋剤としては、具体的には、例えば、（ポリ）エチレングリコール、ジエチレングリコール、（ポリ）プロピレングリコール、トリエチレングリコール、テトラエチレングリコール、１，３−プロパンジオール、ジプロピレングリコール、２，２，４−トリメチル−１，３−ペンタンジオール、（ポリ）グリセリン、２−ブテン−１，４−ジオール、１，４−ブタンジオール、１，５−ペンタンジオール、１，６−ヘキサンジオール、１，２−シクロヘキサンジメタノール、１，２−シクロヘキサノール、トリメチロールプロパン、ジエタノールアミン、トリエタノールアミン、ポリオキシプロピレン、オキシエチレン−オキシプロピレン・ブロック共重合体、ペンタエリスリトール、ソルビトール、ポリビニルアルコール、グルコース、マンニット、ショ糖、ブドウ糖等の多価アルコール；エチレングリコールジグリシジルエーテル、ポリエチレングリコールジグリシジルエーテル、グリセロールポリグリシジルエーテル、ジグリセロールポリグリシジルエーテル、ポリグリセロールポリグリシジルエーテル、（ポリ）プロピレングリコールジグリシジルエーテル等の多価エポキシ化合物；エチレンジアミン、ジエチレントリアミン、トリエチレンテトラミン、テトラエチレンペンタミン、ペンタエチレンヘキサミン、ポリエチレンイミン等の多価アミン化合物；２，４−トリレンジイソシアネート、ヘキサメチレンジイソシアネート等の多価イソシアネート化合物；１，２−エチレンビスオキサゾリン等の多価オキサゾリン化合物；１，３−ジオキソラン−２−オン、４−メチル−１，３−ジオキソラン−２−オン、４，５−ジメチル−１，３−ジオキソラン−２−オン、４，４−ジメチル−１，３−ジオキソラン−２−オン、４−エチル−１，３−ジオキソラン−２−オン、４−ヒドロキシメチル−１，３−ジオキソラン−２−オン、１，３−ジオキサン−２−オン、４−メチル−１，３−ジオキサン−２−オン、４，６−ジメチル−１，３−ジオキサン−２−オン、１，３−ジオキソパン−２−オン等のアルキレンカーボネート化合物；エピクロロヒドリン、エピブロムヒドリン、α−メチルエピクロロヒドリン等のハロエポキシ化合物；亜鉛、カルシウム、マグネシウム、アルミニウム、鉄、ジルコニウム等の多価金属の水酸化物や塩化物等の多価金属化合物；等が挙げられるが、特に限定されるものではない。これら表面架橋剤は、単独で用いてもよく、また、二種類以上を適宜混合して用いてもよい。
【００７８】
表面架橋剤を用いて吸水性樹脂に表面架橋を導入することにより、吸水性樹脂の加圧下における吸水倍率がより一層向上する。また、水性液体に接触したときに該水性液体に溶出する成分、即ち、いわゆる水可溶性成分の量を低減することができる。尚、表面架橋剤の使用量、処理温度、および処理時間は、吸水性樹脂、および用いる表面架橋剤の種類や組み合わせ、所望する表面架橋の度合い等に応じて適宜設定すればよく、特に限定されるものではない。
【００７９】
本発明の吸水性樹脂の製造方法は、以上のように、含水ゲルが内部に有する気泡を練り潰すことなく解砕することができる。さらに、解砕後の含水ゲルは、その内部に気泡が保持されているので、吸水倍率、吸水速度および加圧下における吸水倍率等の吸水特性に優れると共に、水可溶性成分量や残存単量体量が低減された多孔質で粒状の吸水性樹脂を大量かつ簡単に工業的に得ることができる。
【００８０】
本発明の製造方法により得られた吸水性樹脂は、例えば、紙オムツや生理用ナプキン、タンポン、失禁パット、創傷保護材、創傷治癒材等の衛生材料；ペット用の尿等の吸収物品；建材や土壌用保水材、止水材、パッキング材、ゲル水嚢等の土木建築用資材；食品鮮度保持材、食品用ドリップ吸収材、保冷材等の食品用物品；油水分離材、結露吸水シート、凝固材等の各種産業用物品；農園芸用保水材等の農園芸用物品；等の各種用途に好適に用いることができる。
【００８１】
【実施例】
以下、実施例および比較例により、本発明をさらに具体的に説明するが、本発明はこれらにより何ら限定されるものではない。尚、吸水性樹脂の諸性能は、以下の方法で測定した。また、実施例および比較例に記載の「部」は、「重量部」を示す。
【００８２】
（ａ）無加圧下での吸水倍率
吸水性樹脂約０．２ｇを正確に秤量し、５ｃｍ四方の不織布のティーバッグの中に入れ、ヒートシールにより封入した。このティーバッグを、人工尿中に室温で浸漬した。１時間後にティーバッグを引き上げ、遠心分離機を用いて１３００ｒｐｍで３分間液切りを行った後、上記ティーバッグの重量Ｗ₁ （ｇ）を測定した。別途、同様の操作をティーバッグに吸水性樹脂を封入しないで行い、そのときのティーバッグの重量Ｗ₀（ｇ）をブランクとして求めた。吸水倍率は次式
【００８３】
【数１】

に基づいて算出した。
【００８４】
上記の人工尿の組成およびそれらの配合量は、以下の通りである。
【００８５】
人工尿の組成 各組成の配合量
硫酸ナトリウム ０．２００％
塩化カリウム ０．２００％
塩化マグネシウム６水和物 ０．０５０％
塩化カルシウム２水和物 ０．０２５％
リン酸２水素アンモニウム ０．０３５％
リン酸水素２アンモニウム ０．０１５％
脱イオン水 ９９．４７５％
（ｂ）吸水性樹脂の水可溶性成分量
吸水性樹脂０．５ｇを１，０００ｍｌの脱イオン水中に分散させ、１６時間攪拌した後、ろ紙でろ過した。そして、得られたろ液をコロイド滴定することにより、水可溶性成分量（％）を求めた。
【００８６】
（ｃ）吸水性樹脂の残存単量体量
容量２００ｍｌのビーカーに脱イオン水１００ｍｌを入れた後、吸水性樹脂１．０ｇを攪拌しながら加えることにより、該脱イオン水を全てゲル化させた。１時間後、得られたゲルにリン酸水溶液５ｍｌを添加することにより、ゲルを収縮させた。収縮したゲルを攪拌しながらろ紙でろ過し、ろ液、つまり、収縮によって生じた水を、高速液体クロマトグラフィーを用いて分析した。
【００８７】
一方、濃度が既知の単量体水溶液を標準液として、同様に分析し、検量線を得た。そして、この検量線を外部標準に設定し、ろ液の希釈倍率を考慮して、吸水性樹脂の残存単量体量（ｐｐｍ）を求めた。尚、この残存単量体量は、吸水性樹脂の固形分に対する換算値である。
【００８８】
（ｄ）吸水速度
内径５０ｍｍ、高さ７０ｍｍの有底円筒型のポリプロピレン製カップに、吸水性樹脂１．０ｇを入れた。次に、該カップに生理食塩水２８ｇを注いで、該吸水性樹脂に上記生理食塩水を均一に吸収させた。そして、生理食塩水を注いだ時点から、生理食塩水が全てゲル化し、該生理食塩水が吸水性樹脂に全て吸収されて見えなくなる状態になるまでの時間を測定した。該測定を３回繰り返し、これらの平均値を吸水速度（秒）とした。
【００８９】
（ｅ）吸水性樹脂の加圧下の吸水倍率
先ず、加圧下の吸水倍率の測定に用いる測定装置について、図４を参照しながら、以下に簡単に説明する。
【００９０】
図４に示すように、測定装置は、天秤１と、この天秤１上に載置された所定容量の容器２と、外気吸入パイプ３と、シリコーン樹脂からなる導管４と、ガラスフィルタ６と、このガラスフィルタ６上に載置された測定部５とからなっている。上記の容器２は、その頂部に開口部２ａを、その側面部に開口部２ｂをそれぞれ有しており、開口部２ａに外気吸入パイプ３が嵌入される一方、開口部２ｂに導管４が取り付けられている。
【００９１】
また、容器２には、所定量の人工尿１２が入っている。外気吸入パイプ３の下端部は、人工尿１２中に没している。外気吸入パイプ３は、容器２内の圧力をほぼ大気圧に保つために設けられている。上記のガラスフィルタ６は、直径５５ｍｍに形成されている。そして、容器２およびガラスフィルタ６は、導管４によって互いに連通している。また、ガラスフィルタ６は、容器２に対する位置および高さが固定されている。
【００９２】
上記の測定部５は、ろ紙７と、支持円筒９と、この支持円筒９の底部に貼着された金網１０と、重り１１とを有している。そして、測定部５は、ガラスフィルタ６上に、ろ紙７、支持円筒９（つまり金網１０）がこの順に載置されると共に、支持円筒９内部、即ち、金網１０上に重り１１が載置されてなっている。金網１０は、ステンレスからなり、４００メッシュ（目の大きさ３８μｍ）に形成されている。そして、測定時には、金網１０上に、所定量および所定粒子径の吸水性樹脂１５が均一に撒布されるようになっている。また、金網１０の上面、つまり、金網１０と吸水性樹脂１５との接触面の高さは、外気吸入パイプ３の下端面３ａの高さと等しくなるように設定されている。重り１１は、金網１０、即ち、吸水性樹脂１５に対して、５０ｇ／ｃｍ² の荷重を均一に加えることができるように、その重量が調整されている。
【００９３】
上記構成の測定装置を用いて加圧下の吸水倍率を測定した。測定方法について以下に説明する。
【００９４】
先ず、容器２に所定量の人工尿１２を入れる；容器２に外気吸入パイプ３を嵌入する；等の所定の準備動作を行った。次いで、ガラスフィルタ６上にろ紙７を載置した。また、この載置動作に並行して、支持円筒９内部、即ち、金網１０上に、０．９ｇの吸水性樹脂１５を均一に撒布し、この吸水性樹脂１５上に重り１１を載置した。
【００９５】
次いで、ろ紙７上に、金網１０、つまり、吸水性樹脂１５および重り１１を載置した上記支持円筒９を、その中心部がガラスフィルタ６の中心部に一致するように載置した。
【００９６】
そして、ろ紙７上に支持円筒９を載置した時点から、６０分間にわたって経時的に該吸水性樹脂１５が吸収した人工尿１２の重量Ｗ₂ （ｇ）を、天秤１を用いて測定した。また、同様の操作を吸水性樹脂１５を用いないで行い、そのときの重量、つまり、吸水性樹脂１５以外の例えばろ紙７等が吸収した人工尿１２の重量を、天秤１を用いて測定し、ブランク重量Ｗ₃（ｇ）とした。そして、これら重量Ｗ₂ ・Ｗ₃ から、次式、
加圧下の吸水倍率(g/g)＝（重量Ｗ₂(g)−重量Ｗ₃(g)）／吸水性樹脂の重量(g)
に従って加圧下の吸水倍率（ｇ／ｇ）を算出した。
【００９７】
（ｆ）吸水性樹脂の粒子の面積、細孔の面積、細孔面積率および保持率
先ず、含水ゲルをハサミ、回転式解砕機およびミートチョッパーにより解砕した。それぞれの解砕方法で得られた解砕後の含水ゲルを乾燥し、粉砕して得られたそれぞれの吸水性樹脂における粒子の電子顕微鏡（ＳＥＭ）写真撮影を２５倍の拡大倍率で行なった。次いで、それぞれに得られた吸水性樹脂の粒子および細孔が楕円であるとみなして、上記ＳＥＭ写真中の粒子および粒子表面の細孔の、長径および短径をノギスにより測定した。そして次式、
粒子面積（μｍ² ）＝π／４（粒子の長径／写真の倍率）×（粒子の短径／写真の倍率）
細孔面積（μｍ² ）＝π／４（細孔の長径／写真の倍率）×（細孔の短径／写真の倍率）
細孔面積率（％）＝Σ（粒子表面の細孔面積）／Σ（粒子面積）×１００
保持率（％）＝（細孔面積率）／（ハサミで解砕したときの細孔面積率）×１００
に従って吸水性樹脂の粒子の面積、細孔の面積、細孔面積率および保持率を算出した。
【００９８】
〔実施例１〕
アクリル酸８３．２部、３７重量％アクリル酸ナトリウム水溶液１６６２．８部、ポリエチレングリコールジアクリレート（平均エチレンオキサイド（ＥＯ）付加モル数８）５．５部および脱イオン水６５４．５部を混合することにより、アクリル酸の中和率が８５％であり、かつ単量体濃度が３０重量％である単量体水溶液を調整した。
【００９９】
上記単量体水溶液を温度２４℃に保ちながら、液中に窒素ガスを吹き込むことにより、単量体水溶液中の溶存酸素を追い出した。次いで、１０重量％の２，２’−アゾビス（２−メチルプロピオンアミジン）二塩酸塩水溶液７７部を、単量体水溶液に攪拌しながら添加した。
【０１００】
攪拌を開始してから３分後、２，２’−アゾビス（２−メチルプロピオンアミジン）二塩酸塩を加えた単量体水溶液は白濁し、平均粒子径約９μｍの白色の微粒子状固体が生成した。上記該微粒子状固体は、発泡剤としての２，２’−アゾビス（２−メチルプロピオンアミジン）二アクリル酸塩であった。
【０１０１】
さらに、攪拌を開始してから５分後、窒素雰囲気下で攪拌しながらラジカル重合開始剤としての１０重量％過硫酸ナトリウム水溶液１０．８部および１重量％Ｌ−アスコルビン酸水溶液０．５部を上記該単量体水溶液に添加した。そして、上記該水溶液を十分に攪拌した後、静置した。
【０１０２】
１０重量％過硫酸ナトリウム水溶液および１重量％Ｌ−アスコルビン酸水溶液を添加してから３分後に重合反応が始まった。重合反応は湯浴中で行い、上記該水溶液の温度上昇に湯浴の温度を追随させながら行なった。１０重量％過硫酸ナトリウム水溶液を添加してから２６分後、過硫酸ナトリウム水溶液を添加した上記該水溶液の温度は９７℃に達した。その後、温度を７０℃〜９０℃の範囲内に保ちながら、さらに２０分間上記該水溶液を静置してアクリル酸塩系単量体の重合反応を完了させた。これにより、多孔質の架橋重合体である気泡を有する含水ゲルを得た。
【０１０３】
次いで、上記含水ゲルを前述の回転式解砕機により連続的に解砕した。解砕中の回転式解砕機における含水ゲルの平均滞留時間、つまり解砕時間は、約０．２５分間であった。解砕後の含水ゲルの大きさは、その粒子径が約１ｍｍ〜１５ｍｍの範囲内であった。
【０１０４】
解砕後の含水ゲルを循環式熱風乾燥機で１６０℃、１時間乾燥した。ついで、乾燥後の含水ゲルをロールミルで粉砕し、さらにＪＩＳ規格の標準篩いにより、メッシュの大きさが８５０μｍの篩いを通過し、１５０μｍの篩い上に残る粒子径を有する本発明の吸水性樹脂（１）を得た。得られた本発明の吸水性樹脂（１）の諸性能を測定した結果を表１に記載した。
【０１０５】
さらに、上記吸水性樹脂（１）のＳＥＭ写真撮影を２５倍の倍率で行い、粒子および粒子表面の細孔の長径および短径をノギスで測定することにより、吸水性樹脂の粒子の面積、細孔の面積、細孔面積率および保持率を算出した。上記吸水性樹脂（１）のＳＥＭ写真を図１に、計算結果を表２に示す。
【０１０６】
〔比較例１〕
先ず、気泡を有する含水ゲルを製造した。即ち、実施例１の操作および反応と同様の操作および反応を行うことにより、気泡を有する含水ゲルを得た。さらに、この含水ゲルを口径が８ｍｍのロストルを有するミートチョッパーを用いて解砕した他は実施例１と同様の操作を行って、比較用の吸水性樹脂（１）を得た。解砕には、約５分間を要した。得られた比較用の吸水性樹脂（１）の諸性能を測定した結果を表１に記載した。
【０１０７】
さらに、上記比較用の吸水性樹脂（１）のＳＥＭ写真撮影を２５倍の倍率で行い、粒子および粒子表面の細孔の長径および短径をノギスで測定することにより、比較用の吸水性樹脂（１）の粒子の面積、細孔の面積、細孔面積率および保持率を算出した。上記比較用の吸水性樹脂（１）のＳＥＭ写真を図２に、計算結果を表２に示す。
【０１０８】
〔比較例２〕
先ず、気泡を有する含水ゲルを製造した。即ち、実施例１の操作および反応と同様の操作および反応を行うことにより、気泡を有する含水ゲルを得た。さらに、この含水ゲルをハサミで粒子径が約１ｍｍ〜５ｍｍの範囲内になるように手で細断して解砕した他は実施例１と同様の操作を行って、比較用の吸水性樹脂（２）を得た。解砕には、約３０分間を要した。得られた比較用の吸水性樹脂（２）の諸性能を測定した結果を表１に記載した。
【０１０９】
さらに、上記比較用の吸水性樹脂（２）のＳＥＭ写真撮影を２５倍の倍率で行い、粒子および粒子表面の細孔の長径および短径をノギスで測定することにより、上記比較用の吸水性樹脂（２）の粒子の面積、細孔の面積、細孔面積率および保持率を算出した。上記比較用の吸水性樹脂（２）のＳＥＭ写真を図３に、計算結果を表２に示す。
【０１１０】
〔実施例２〕
アクリル酸２７部、３７重量％アクリル酸ナトリウム水溶液２８５部、ポリエチレングリコールジアクリレート（平均ＥＯ付加モル数８）１．１部、および脱イオン水１１７．６部を混合することにより単量体水溶液を調整した。単量体水溶液はアクリル酸の中和率が７５％であり、かつ単量体濃度が３１重量％の水溶液である。
【０１１１】
上記単量体水溶液を１６℃に保ちながら、液中に窒素ガスを吹き込むことにより、単量体水溶液中の溶存酸素を除去した。次いで、攪拌しながら親水親油バランス（Hydrophile-lypophile balance:HLB）が１４．９の界面活性剤であるポリオキシエチレンソルビタンモノステアレートの１重量％水溶液８．９部を添加した。
【０１１２】
次いで、窒素雰囲気下で攪拌しながらラジカル重合開始剤としての１０重量％過硫酸ナトリウム水溶液２．１部および１重量％Ｌ−アスコルビン酸水溶液０．１部を上記該単量体水溶液に添加した。そして、上記該水溶液を十分に攪拌した後、静置した。
【０１１３】
１０重量％過硫酸ナトリウム水溶液および１重量％Ｌ−アスコルビン酸水溶液を添加してから４分後、単量体水溶液が白濁し始め、重合反応を開始したので、微粉末の炭酸ナトリウム１．８部を添加した。重合反応は湯浴中で行い、上記該水溶液の温度上昇に湯浴の温度を追随させながら行なった。１０重量％過硫酸ナトリウムを上記該水溶液に添加してから３７分後、上記該水溶液の温度は約９３℃に達した。
【０１１４】
その後、温度を７０℃〜９０℃の範囲内に保ちながら、さらに２０分間単量体水溶液を静置してアクリル酸塩系単量体の重合反応を完了させた。これにより、多孔質の架橋重合体である気泡を有する含水ゲルを得た。
【０１１５】
さらに、上記該含水ゲルを前述の回転式解砕機により連続的に解砕した。解砕中の回転式解砕機における含水ゲルの平均滞留時間、つまり解砕時間は、約０．１６分間であった。解砕後の含水ゲルの大きさは、その粒子径が約２ｍｍ〜１５
ｍｍの範囲内であった。
【０１１６】
解砕後の含水ゲルを循環式熱風乾燥機で１６０℃、１時間乾燥した。ついで、乾燥後の含水ゲルをロールミルで粉砕し、さらにＪＩＳ規格の標準篩いにより、メッシュの大きさが８５０μｍの篩いを通過し、１５０μｍの篩い上に残る粒子径を有する本発明の吸水性樹脂（２）を得た。得られた本発明の吸水性樹脂（２）の諸性能を測定した結果を表１に記載した。
【０１１７】
〔比較例３〕
先ず、気泡を内部に有する含水ゲルを製造した。即ち、実施例２の操作および反応と同様の操作および反応を行うことにより、気泡を有する含水ゲルを得た。さらに、この含水ゲルを口径が８ｍｍのロストルを有するミートチョッパーを用いて解砕した他は実施例２と同様の操作を行って、比較用の吸水性樹脂（３）を得た。解砕には、約４分間を要した。得られた比較用の吸水性樹脂（３）の諸性能を測定した結果を表１に記載した。
【０１１８】
〔比較例４〕
先ず、気泡を内部に有する含水ゲルを製造した。即ち、実施例２の操作および反応と同様の操作および反応を行うことにより、気泡を有する含水ゲルを得た。さらに、この含水ゲルをハサミで粒子径が約１ｍｍ〜５ｍｍの範囲内になるように手で細断して解砕した他は実施例１と同様の操作を行って、比較用の吸水性樹脂（４）を得た。解砕には、約３０分間を要した。得られた比較用の吸水性樹脂（４）の諸性能を測定した結果を表１に記載した。
【０１１９】
〔実施例３〕
先ず、実施例１で得られた本発明の吸水性樹脂（１）に対して、二次架橋処理を施した。すなわち、二次架橋処理用の処理液は、エチレングリコールジグリシジルエーテル０．０５部、乳酸０．５部、ポリオキシエチレンソルビタンモノステアレート０．０２部、イソプロピルアルコール０．７５部および水３部を混合することにより調整した。
【０１２０】
次いで、実施例１で得られた本発明の吸水性樹脂（１）１００部と上記該処理液とを混合し、得られた混合物を１９５℃で３０分間加熱処理し、本発明の吸水性樹脂（３）を得た。得られた本発明の吸水性樹脂（３）の諸性能を測定した結果を表１に記載した。
【０１２１】
〔実施例４〕
先ず、実施例２で得られた本発明の吸水性樹脂（２）に対して、二次架橋処理を施した。すなわち、二次架橋処理用の処理液は、グリセリン１部、エチルアルコール１．７５部および水３部を混合することにより調整した。
【０１２２】
次いで、実施例２で得られた本発明の吸水性樹脂（２）１００部と上記該処理液とを混合し、得られた混合物を１９５℃で３０分間加熱処理し、本発明の吸水性樹脂（４）を得た。得られた本発明の吸水性樹脂（４）の諸性能を測定した結果を表１に記載した。
【０１２３】
〔実施例５〕
アクリル酸２７．０部、３７重量％アクリル酸ナトリウム水溶液２８５．０部、ポリエチレングリコールジアクリレート（平均ＥＯ付加モル数８）１．１部、フッ素系カチオン性界面活性剤（商品名；フロラードＦＣ−１３５、住友スリーエム株式会社製）０．０１３部および脱イオン水１１７．６部を混合することにより、単量体水溶液を調整した。
【０１２４】
上記単量体水溶液を高速ホモディスパにより高速（３，０００ｒｐｍ）で強攪拌しながら、液中に窒素ガスを吹き込むことにより、単量体水溶液中の溶存酸素を追い出し、単量体水溶液中に窒素からなる気泡を分散させた。単量体水溶液中に窒素ガスが均一に分散し、その体積が１．２５倍になった時点で、高速強攪拌下にて、１０重量％過硫酸ナトリウム水溶液２．１部および１０重量％亜硫酸水素ナトリウム水溶液２．１部添加し、直ちに重合反応を開始させ、単量体水溶液中に気泡が分散した状態で、温度２５℃〜７５℃の範囲内にし、２時間静置重合した。これにより、内部に気泡の分散した含水ゲルを得た。
【０１２５】
次いで、上記含水ゲルを前述の回転式解砕機により連続的に解砕した。解砕中の回転式解砕機における含水ゲルの平均滞留時間、すなわち解砕時間は、約０．１６分間であった。解砕後の含水ゲルの大きさは、その粒子径が約２ｍｍ〜１５ｍｍの範囲内であった。
【０１２６】
解砕後の含水ゲルを循環式熱風乾燥機で１６０℃、１時間乾燥した。次いで、乾燥後の含水ゲルをロールミルで粉砕し、さらにＪＩＳ規格の標準篩いにより、メッシュの大きさが８５０μｍの篩いを通過し、１５０μｍの篩い上に残る粒子径を有する本発明の吸水性樹脂（５）を得た。得られた本発明の吸水性樹脂（５）の諸性能を測定した結果を表１に記載した。
【０１２７】
〔比較例５〕
先ず、気泡を内部に有する含水ゲルを製造した。即ち、実施例５の操作および反応と同様の操作および反応を行うことにより、気泡を有する含水ゲルを得た。さらに、この含水ゲルを口径が８ｍｍのロストルを有するミートチョッパーを用いて解砕した他は実施例５と同様の操作を行って、比較用の吸水性樹脂（５）を得た。解砕には、約５分間を要した。得られた比較用の吸水性樹脂（５）の諸性能を測定した結果を表１に記載した。
【０１２８】
〔比較例６〕
先ず、気泡を内部に有する含水ゲルを製造した。即ち、実施例５の操作および反応と同様の操作および反応を行うことにより、気泡を有する含水ゲルを得た。さらに、この含水ゲルを口径が８ｍｍのロストルを有するミートチョッパーを用いて解砕した他は実施例５と同様の操作を行って、比較用の吸水性樹脂（６）を得た。解砕には、約３０分間を要した。得られた比較用の吸水性樹脂（６）の諸性能を測定した結果を表１に記載した。
【０１２９】
【表１】

【０１３０】
【表２】

表１に記載された上記実施例１〜５の結果から明らかなように、本発明にかかる製造方法によって得られた吸水性樹脂は、気泡を十分に保持していることにより、無加圧下での吸水倍率、吸水速度および加圧下における吸水倍率等の吸水特性に優れると共に、水可溶性成分量や残存単量体量が低減されていることがわかる。また、本願発明では、上記実施例１〜５と比較例２および４との比較から、解砕時間の大幅な低減と解砕操作の簡便化が図れて、工業的な生産が可能であることがわかる。
【０１３１】
【発明の効果】
本発明に係る吸水性樹脂の製造方法は、以上のように、解砕は、固定刃と回転刃とによる含水ゲルの剪断によって解砕する方法である。
【０１３２】
それゆえ、上記方法では、剪断によって含水ゲルが解砕されるため、従来のように解砕時に気泡が押し潰されることが抑制される。また、上記方法では、含水ゲルを連続的に解砕できるので、気泡の減少を抑制しながら、解砕効率を向上でき、生産性を改善できる。この結果、上記方法では、吸水倍率、吸水速度および加圧下における吸水倍率等の吸水特性に優れると共に、水可溶性成分量や残存単量体量が低減された吸水性樹脂を大量かつ簡単に、工業的に得ることができるという効果を奏する。
【０１３３】
また、本発明に係る吸水性樹脂の製造方法は、以上のように、解砕は、垂直な回転軸を有する回転刃による遠心力により、含水ゲルが固定刃と回転刃との間に押し出されて行われる方法である。
【０１３４】
これにより、上記方法では、解砕は、内部に気泡を含む含水ゲルが遠心力により移動して、固定刃と回転刃とにより剪断されて行われるので、従来のように押圧や、スクリューによる押圧による移動と比べて含水ゲルに対し、均一に移動方向への力が加わるため、含水ゲルにおける気泡が押しつぶされることを抑制しながら剪断によって解砕することができる。それゆえ、上記方法では、気泡の減少が抑制されて、気泡による多孔質な吸水性樹脂が安定に、かつ、簡便に得られるので、無加圧下での吸水倍率、吸水速度および加圧下における吸水倍率等の吸水特性に優れた吸水性樹脂を大量かつ簡単に工業的に得ることができるという効果を奏する。
【０１３５】
本発明に係る吸水性樹脂の製造方法は、以上のように、エチレン性不飽和単量体を架橋剤の存在下で気泡を含有するように重合して得られる含水ゲルを、上記気泡の減少が抑制、例えば上記気泡が２０％以上保持されるように解砕する方法である。
【０１３６】
これにより、上記方法では、含水ゲルが内部に有する気泡の減少が抑制されるように解砕することで、内部の気泡を練り潰すことを抑制しながら解砕することができる。それゆえ、解砕後の含水ゲルは、その内部に気泡を保持されているので、無加圧下での吸水倍率、吸水速度および加圧下における吸水倍率等の吸水特性に優れると共に、水可溶性成分量や残存単量体量が低減された吸水性樹脂を安定に得ることができるという効果を奏する。
【０１３７】
本発明に係る吸水性樹脂の製造方法は、以上のように、含水ゲルは、エチレン性不飽和単量体および架橋剤を含む水溶液に不活性ガスの気泡を分散させた状態で上記エチレン性不飽和単量体および架橋剤を重合して得られる方法である。
【０１３８】
これにより、上記方法では、不活性ガスが重合反応を阻害しないので、内部に気泡を有する多孔質な含水ゲルが安定に得られ、無加圧下での吸水倍率、吸水速度および加圧下における吸水倍率等の吸水特性に優れた吸水性樹脂を安定に得ることができるという効果を奏する。
【０１３９】
本発明に係る吸水性樹脂の製造方法は、以上のように、さらに、含水ゲルを解砕して得られた粒子状物の表面近傍を二次架橋する方法である。
【０１４０】
これにより、上記方法では、二次架橋によって、吸水性樹脂の加圧下における吸水倍率がより一層向上し、また、水性液体に接触したときに該水性液体に溶出する成分、すなわち、水の可溶性成分の量、および残存単量体量を二次架橋により低減した吸水性樹脂が得られるという効果を奏する。
【図面の簡単な説明】
【図１】 本発明の吸水性樹脂の製造方法における、実施例１に記載の吸水性樹脂の粒子構造を電子顕微鏡写真（２５倍）によって示す図面代用写真である。
【図２】 上記製造方法の各実施例に対する、比較例１に記載の比較用吸水性樹脂の粒子構造を電子顕微鏡写真（２５倍）によって示す図面代用写真である。
【図３】 上記製造方法の各実施例に対する、比較例２に記載の比較用吸水性樹脂の粒子構造を電子顕微鏡写真（２５倍）によって示す図面代用写真である。
【図４】 上記製造方法における、吸水性樹脂の加圧下での吸水倍率の測定に用いる測定装置の概略の断面図である。
【符号の説明】
１ 天秤
２ 容器
３ 外気吸入パイプ
４ 導管
５ 測定部
６ ガラスフィルタ
７ ろ紙
９ 支持円筒
１０ 金網
１１ 重り
１２ 人工尿
１５ 吸水性樹脂[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a water-absorbent resin suitably used for various applications such as sanitary materials such as paper diapers and incontinence pads, soil water retention materials, food freshness retention materials, agricultural and horticultural water retention materials, and the like. .
[0002]
[Prior art]
In recent years, sanitary materials such as paper diapers, sanitary napkins, incontinence pads, etc. are contaminated with clothing, etc. due to the above body fluid by absorbing and holding discharged body fluids such as urine and blood as constituent materials. For the purpose of preventing, particulate water-absorbing resins are widely used. Furthermore, recently, in order to reduce the thickness and performance of the sanitary material, the fiber base material such as pulp is reduced from the sanitary material, and the amount of water-absorbing resin is reduced.
There is a tendency to increase, and further improvement of the water absorption performance of the water absorbent resin is required.
[0003]
Therefore, in order to meet the above requirements, for example, a method of increasing the surface area of the water-absorbing resin is known as a method for improving the water-absorbing performance of the water-absorbing resin, in particular, the water absorption magnification and the water absorption speed. However, simply increasing the particle diameter in order to increase the surface area causes a problem that liquid permeability in the particulate water-absorbing resin is lowered.
[0004]
For this reason, as a method for increasing the surface area without reducing the particle diameter, conventionally, a foaming agent is used during polymerization or crosslinking, and bubbles are contained in the particles of the water-absorbent resin to make the water-absorbent resin porous. A method of forming particles (for example, JP-A-5-237378, JP-A-7-185331, International Publication WO95 / 2002) has been proposed.
[0005]
As a method for producing such a water-absorbent resin, an ethylenically unsaturated monomer is polymerized in the presence of a cross-linking agent and a foaming agent, and the resulting hydrogel containing bubbles is further dried. In order to increase, it was considered that first, after coarsely crushing, drying and pulverization were performed to obtain a particulate porous water-absorbent resin. Examples of the method for crushing the hydrogel include a method of crushing with a screw type extruder such as a meat chopper, a method of crushing with scissors, or a method of crushing the hydrogel while polymerizing in a kneader. It was.
[0006]
Japanese Patent Publication No. 3-2042 discloses a method for crushing a water-soluble polymer gel by rotating two roller-type cutters and biting the water-soluble polymer gel between the roller-type cutters. Thus, a method for crushing is disclosed.
[0007]
[Problems to be solved by the invention]
However, in the conventional method of crushing with a meat chopper or kneader, the hydrated gel is crushed while being kneaded with a meat chopper or the like. As a result, when the water-containing gel containing bubbles is crushed with a meat chopper or the like, the bubbles are crushed and significantly reduced, and the surface area of the obtained water-absorbent resin is reduced. The water absorption rate is slow, and therefore, the water absorption property is inferior.
[0008]
Further, in the conventional crushing method using scissors, the bubbles contained in the water-containing gel are not crushed and the resulting water-absorbent resin has good water-absorbing properties, but the productivity is low, and There is a problem that industrial production is almost impossible.
[0009]
Furthermore, since the crushing method described in the above-mentioned conventional publication does not consider any polymer gel containing bubbles, the polymer gel is inserted between two roller-type cutters, cut and crushed, In order to extrude the polymer gel after crushing, the bubbles are crushed and the bubbles are remarkably reduced. For this reason, the water-absorbent resin obtained by the method described in the above-mentioned conventional publication has only a problem that the water-absorbing property is inferior because the surface area is reduced because only the bubbles are remarkably reduced. ing. Therefore, conventionally, a method for producing a porous water-absorbent resin having high bubble retention even after crushing a water-containing gel containing bubbles and high productivity capable of industrial production has been desired. Yes.
[0010]
The present invention has been made in view of the above-described conventional problems, and its purpose is to produce as many bubbles as possible in the interior of a water-containing resin by crushing a hydrogel containing bubbles in the interior. Is to provide a method for producing a water-absorbent resin excellent in water absorption characteristics.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned conventional problems, the inventors of the present application have made extensive studies on a method for producing a water-absorbent resin. As a result, when the water-containing gel containing bubbles is crushed, a method has been found in which the bubbles contained in the water-containing gel are maintained at 20% or more, and the present invention has been completed.
[0012]
That is, According to the present invention In order to solve the above-described problem, a method for producing a water-absorbent resin is a method of rotating a water-containing gel obtained by polymerizing an ethylenically unsaturated monomer so as to contain bubbles in the presence of a crosslinking agent, and rotating it with a fixed blade. Blade and With a rotary crusher in which the retention time of the hydrogel is 1 second or more and less than 3 minutes Crush by shear And then dry It is characterized by doing.
[0013]
Further, according to the present invention In order to solve the above problems, a method for producing a water absorbent resin the above The crushing is characterized in that the hydrogel is pushed out between the fixed blade and the rotary blade by the centrifugal force generated by the rotary blade having a vertical rotating shaft.
[0014]
According to the above method, the crushing is performed by shearing with the stationary blade and the rotating blade of the hydrogel containing bubbles inside, thereby breaking down the hydrogel while suppressing the bubbles of the hydrogel from being crushed. Can be crushed. Therefore, in the above method, since the hydrogel can be continuously crushed by shearing between the fixed blade and the rotary blade, the reduction of bubbles is suppressed, and the porous water-absorbent resin due to the bubbles is stable, and It is possible to easily and industrially obtain a large amount of a water-absorbent resin which is easily obtained and has excellent water absorption characteristics such as a water absorption capacity under no pressure, a water absorption speed and a water absorption capacity under pressure.
[0015]
According to the present invention In order to solve the above problems, a method for producing a water absorbent resin Contains hydrous gel It is characterized by crushing so that the reduction of bubbles is suppressed.
[0016]
According to said method, it can crush, suppressing crushing of an internal bubble by crushing the hydrogel which contains a bubble inside so that the reduction | decrease of the said bubble may be suppressed. Therefore, in the above method, the reduction of bubbles is suppressed, and a porous water-absorbent resin due to the bubbles can be stably obtained. Thus, the water absorption characteristics such as the water absorption capacity under no pressure, the water absorption speed, and the water absorption capacity under pressure. Can be obtained.
[0017]
Also, According to the present invention In order to solve the above problems, the method for producing a water absorbent resin of the invention the above The hydrogel after crushing is characterized in that air bubbles are maintained at 20% or more.
[0018]
According to the above method, when the hydrated gel containing bubbles is crushed, the porosity of the obtained water-absorbent resin can be further maintained by maintaining 20% or more of the bubbles contained in the hydrated gel. Further, it is possible to obtain a water-absorbing resin that is more excellent due to water absorption characteristics such as a water absorption capacity under no pressure, a water absorption speed, and a water absorption capacity under pressure.
[0019]
According to the present invention In order to solve the above problems, a method for producing a water absorbent resin Contains the bubbles The hydrogel is Acrylate system Contains monomer and crosslinker And the monomer concentration is 20% to 60% by weight. In the state where inert gas bubbles are dispersed in an aqueous solution, Acrylate system It is obtained by polymerizing a monomer and a crosslinking agent.
[0020]
According to the above method, since the inert gas has no adverse effect on the polymerization reaction, a porous water-containing gel having a large number of bubbles inside can be stably obtained. Can be obtained stably.
[0021]
According to the present invention A method for producing a water-absorbent resin is to solve the above problems. To In addition, the hydrogel is crushed Dry It is characterized in that the surface vicinity of the particulate matter obtained in this way is subjected to secondary crosslinking.
[0022]
According to the above method, the water-absorbing capacity under pressure of the water-absorbent resin is further improved by the secondary cross-linking, and the component that elutes into the aqueous liquid when contacted with the aqueous liquid, that is, a so-called water-soluble component It is possible to obtain a water-absorbent resin in which the amount of is reduced by secondary crosslinking.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below. The method for producing a water-absorbent resin according to the present invention is a method for producing a water-containing gel obtained by polymerizing a monomer component containing an ethylenically unsaturated monomer so as to contain bubbles in the presence of a crosslinking agent. This is a method for producing a water-absorbent resin that is crushed so as to suppress the decrease in the number of bubbles and retains bubbles of 20% or more.
[0024]
The ethylenically unsaturated monomer (hereinafter referred to as a monomer) used as a raw material in the present invention has water solubility. Specific examples of the monomer include (meth) acrylic acid, β-acryloyloxypropionic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, cinnamic acid, rubinic acid, 2 -(Meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, vinylsulfonic acid, styrenesulfonic acid, allylsulfonic acid, vinylphosphonic acid, 2 -Acid group-containing monomers such as (meth) acryloyloxyethyl phosphoric acid, and alkali metal salts, alkaline earth metal salts, ammonium salts, alkylamine salts thereof; N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopro Dialkylaminoalkyl (meth) acrylates such as ru (meth) acrylamide and their quaternized compounds (for example, reactants with alkyl hydrides, reactants with dialkyl sulfate, etc .; dialkylaminohydroxyalkyl (meth) acrylates and these N-alkylvinylpyridinium halides; hydroxyalkyl (meth) acrylates such as hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate; 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, polyethylene glycol mono (meth) acrylate; vinylpyridine, N-vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine; N-vinylacetamide Vinyl acetate, alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, etc. These monomers may be used alone or in combination of two or more. You may mix and use suitably.
[0025]
Among the above-exemplified monomers, an ethylenically unsaturated monomer containing an acrylate monomer as a main component is preferable because the water absorption properties and safety of the resulting hydrogel are further improved. Here, the acrylate monomer refers to acrylic acid and / or water-soluble salts of acrylic acid. The water-soluble salts of acrylic acid are alkali metal salts and alkaline earths of acrylic acid having a neutralization rate in the range of 30 mol% to 100 mol%, preferably in the range of 50 mol% to 99 mol%. Metal salt, ammonium salt, hydroxyammonium salt, amine salt, alkylamine salt are shown. Of the water-soluble salts exemplified above, sodium salts and potassium salts are more preferable. These acrylate monomers may be used alone or in combination of two or more. The average molecular weight (degree of polymerization) of the water absorbent resin is not particularly limited.
[0026]
In addition, the monomer component contains other monomer (hereinafter referred to as a copolymer) copolymerizable with the monomer to such an extent that the hydrophilicity of the resulting hydrogel is not substantially inhibited. May be. Specific examples of the copolymer include (meth) acrylic esters such as methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate; vinyl acetate, vinyl propionate, and the like. A hydrophobic monomer; and the like. These copolymers may be used alone, or two or more kinds may be appropriately mixed and used.
[0027]
The water-containing gel according to the present invention can be obtained by polymerizing the monomer component using an aqueous solvent. At the start of polymerization in the above polymerization reaction, for example, a polymerization initiator or activation energy rays such as radiation, electron beam, ultraviolet ray, electromagnetic ray, or the like can be used. Specific examples of the polymerization initiator include inorganic peroxides such as sodium persulfate, ammonium persulfate, potassium persulfate, and hydrogen peroxide; t-butyl hydroperoxide, benzoyl peroxide, cumene hydroper Organic peroxides such as oxide; 2,2′-azobis (N, N′-dimethyleneisobutylamidine) or a salt thereof, 2,2′-azobis (2-methylpropionamidine) or a salt thereof, 2,2 ′ -Radical polymerization initiators such as -azobis (2-amidinopropane) or a salt thereof, an azo compound such as 4,4'-azobis-4-cyanovaleric acid; and the like. These polymerization initiators may be used alone or in combination of two or more. Moreover, when using a peroxide as a polymerization initiator, you may perform oxidation-reduction (redox) polymerization using reducing agents, such as a sulfite, a bisulfite, and L-ascorbic acid, for example.
[0028]
Examples of the crosslinking agent used when polymerizing the monomer in the present invention include a compound having a plurality of vinyl groups in the molecule; a plurality of functional groups capable of reacting with a carboxyl group or a sulfonic acid group in the molecule. And the like. this
These crosslinking agents may be used alone or in combination of two or more.
[0029]
Specific examples of the compound having a plurality of vinyl groups in the molecule include N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, and (poly) propylene glycol di (meth). Acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate , Dipentaerythritol hexa (meth) acrylate, N, N-diallylacrylamide, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallyl And poly (meth) allyloxyalkanes such as amine, diallyloxyacetic acid, N-methyl-N-vinylacrylamide, bis (N-vinylcarboxylic acid amide), and tetraallyloxyethane.
[0030]
Examples of the compound having a plurality of functional groups capable of reacting with a carboxyl group or a sulfonic acid group in the molecule include (poly) ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, 1,3- Propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, polypropylene glycol, (poly) glycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,5 -Pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethyleneoxypropylene Polyhydric alcohol compounds such as polyblock copolymers, pentaerythritol, sorbitol; (poly) ethylene glycol diglycidyl ether, (poly) glycerol polyglycidyl ether, diglycerol polyglycidyl ether, (poly) propylene glycol diglycidyl ether, glycidol Epoxy compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyamidepolyamine, polyethyleneimine, and the like, and condensates of these polyamines and haloepoxy compounds; Polyvalent isocyanate compounds such as 4-tolylene diisocyanate and hexamethylene diisocyanate; polyvalent ox such as 1,2-ethylenebisoxazoline Zolin compounds; Silane coupling agents such as γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltrimethoxysilane; 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxy Methyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxane-2- Alkylene carbonate compounds such as ON and 1,3-dioxopan-2-one; haloepoxy compounds such as epichlorohydrin, epibromohydrin and α-methylepichlorohydrin And hydroxides or chlorides of polyvalent metals such as zinc, calcium, magnesium, aluminum, iron, and zirconium.
[0031]
The amount of the crosslinking agent used is not particularly limited, but is preferably in the range of 0.0001 mol% (based on monomer) to 10 mol%, preferably 0.001 mol% to 1 mol%. It is more preferable to be within the range.
[0032]
When the monomer is polymerized in the presence of a crosslinking agent, in order to improve the water absorption characteristics of the resulting water absorbent resin and efficiently perform foaming with a foaming agent for containing bubbles in the hydrogel, It is preferable to make the said monomer and a crosslinking agent into aqueous solution. That is, it is preferable to use water as a solvent. The concentration of the monomer in the aqueous solution (hereinafter referred to as the monomer aqueous solution) is more preferably in the range of 20% by weight to 60% by weight. When the concentration of the monomer is less than 20% by weight, the amount of water-soluble components in the resulting water-absorbent resin may increase, and foaming by the foaming agent may be insufficient to improve the water absorption rate. There is a fear. On the other hand, when the concentration of the monomer exceeds 60% by weight, it may be difficult to control the reaction temperature and foaming by the foaming agent.
[0033]
Moreover, water and the organic solvent soluble in water can also be used together as a solvent of monomer aqueous solution. Specific examples of the organic solvent include methyl alcohol, ethyl alcohol, acetone, dimethyl sulfoxide, ethylene glycol monomethyl ether, glycerin, (poly) ethylene glycol, (poly) propylene glycol, and alkylene carbonate. These organic solvents may be used alone or in combination of two or more.
[0034]
In the present invention, the hydrogel obtained by polymerizing the above monomers needs to contain bubbles inside. The method for incorporating bubbles inside is not particularly limited, and can be obtained, for example, by polymerizing the aqueous monomer solution in the presence of a foaming agent. The foaming agent may be added to the monomer aqueous solution before the monomer aqueous solution is polymerized, or may be added to the monomer aqueous solution during the polymerization. Furthermore, you may add to the obtained water-containing gel after superposition | polymerization of monomer aqueous solution.
[0035]
As the foaming agent, those that are dispersed or dissolved in the aqueous monomer solution can be used. A volatile organic solvent that is dispersed or dissolved in the aqueous monomer solution, water and an organic solvent that is sparingly soluble at room temperature. Examples thereof include compounds, carbonates, and dry ice. Specific examples of the blowing agent include n-pentane, 2-methylbutane, 2,2-dimethylpropane, hexane, heptane, benzene, substituted benzene, chloromethane, chloroethane, chlorofluoromethane, 1, 1,2-trichlorotrifluoroethane, methanol, ethanol, isopropanol, acetone, azodicarbonamide, azobisisobutyronitrile, barium azodicarboxylate, dinitrosopentamethylenetetramine, 4,4′-oxybis (benzenesulfonylhydra) Did), paratoluenesulfonyl hydrazide, diazoaminobenzene, N, N′-dimethyl-N, N′-dinitrosotephthalamide, nitrourea, acetone-p-toluenesulfonylhydrazone, p-toluenesulfonyl azide, 2 4-toluenedisulfonyl hydrazide, p-methylurethanebenzenesulfonyl hydrazide, trinitrosotrimethylenetriamine, p-toluenesulfonyl semicarbazide, oxalyl hydrazide, nitroguanidine, hydrazodicarbonamide, trihydrazinotriamine, azobisformamide, benzene Sulfonyl hydrazide, benzene-1,3-disulfonyl hydrazide, diphenylsulfone-3,3′-disulfonyl hydrazide, 4,4′-oxybis (benzenesulfonyl hydrazide), sulfonic hydrazide, malonic acid and its salt, carbamic acid and its Organic compounds such as salts; sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonium nitrite, basic magnesium carbonate, calcium carbonate, etc. Inorganic compounds such as carbonates;
General formula (1)
[0036]
[Chemical 1]

(Where X ₁ , X ₂ Each independently represents an alkylene group having 1 to 4 carbon atoms; ₁ , R ₂ , R _Three , R _Four , R _Five , R ₆ Each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an aryl group, an allyl group, or a benzyl group) or the general formula (2)
[0037]
[Chemical formula 2]

(Where X _Three , X _Four Each independently represents an alkylene group having 1 to 4 carbon atoms; _Five , X ₆ Each independently represents an alkylene group having 2 to 4 carbon atoms, R ₇ , R ₈ Each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms)
An acrylic acid salt of an amino group-containing azo compound represented by: These foaming agents may be used alone or in combination of two or more. When a carbonate such as sodium carbonate is used, it is preferable to use a surfactant or a dispersant. By using a surfactant or a dispersant, it is possible to prevent the average bubble diameter of the bubbles of the resulting hydrogel from becoming too large and slowing the absorption rate.
[0038]
Among the foaming agents exemplified above, an acrylate salt of an amino group-containing azo compound is more preferable. The acrylic acid salt of an amino group-containing azo compound has an average particle diameter of a predetermined value even without using a dispersion stabilizer such as a surfactant or a water-soluble polymer, or without stirring the aqueous monomer solution. While maintaining the value, it can be uniformly dispersed in the monomer aqueous solution in a stationary state, and does not cause sedimentation, floating or separation. Acrylates of amino group-containing azo compounds are particularly excellent in dispersibility with respect to acrylate monomers.
[0039]
Specific examples of the acrylate salt of the amino group-containing azo compound represented by the general formula (1) or the general formula (2) include 2,2′-azobis (2-methyl-N-phenylpropion). Amidine) diacrylate, 2,2′-azobis [N- (4-chlorophenyl) -2-methyl-propionamidine] diacrylate, 2,2′-azobis [N- (4-hydroxyphenyl)- 2-methylpropionamidine] diacrylate, 2,2′-azobis [2-methyl-N- (phenylmethyl) -propionamidine] diacrylate, 2,2′-azobis [2-methyl-N— (2-propenyl) propionamidine] diacrylate, 2,2′-azobis (2-methylpropionamidine) diacrylate, 2,2′-azobis [N- (2-hydroxyethyl) ) -2-Methyl-propionamidine] diacrylate, 2,2′-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] diaacrylate, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] diacrylate, 2,2′-azobis- [2- (4,5,6,7-tetrahydro-1H-1,3-diazepine-2- Yl) propane] diacrylate, 2,2′-azobis [2- (3,4,5,6-tetrahydropyrimidin-2-yl) propane] diacrylate, 2,2′-azobis [2- (5-Hydroxy-3,4,5,6-tetrahydropyrimidin-2-yl) propane] diacrylate, 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazoline- 2-yl] propane} diacrylate Although the like, but is not particularly limited.
[0040]
The acrylate of the amino group-containing azo compound can be isolated by, for example, using a method such as filtration after precipitation in an aqueous monomer solution. In addition, when the acrylate of the amino group-containing azo compound is precipitated in the monomer aqueous solution, the monomer aqueous solution may be cooled as necessary.
[0041]
The foaming agent prepared above may be used by adding it to the monomer aqueous solution, and the foaming agent precursor (hereinafter referred to as the foaming agent precursor) is dissolved in the monomer aqueous solution. Then, if necessary, it can be prepared in the monomer aqueous solution by adding carbon dioxide gas or acrylate to the monomer aqueous solution. That is, the foaming agent can be precipitated by reacting the foaming agent precursor with carbon dioxide gas or acrylate in an aqueous monomer solution. As the acrylate, sodium acrylate is preferred. Further, when the monomer is an acrylate monomer, the monomer can act as an acrylate.
[0042]
The acrylate of the amino group-containing azo compound has a function as a foaming agent and a function as a radical polymerization initiator. Then, by polymerizing the monomer in the presence of the acrylate of the amino group-containing azo compound, it is possible to obtain a water-absorbing resin in which the amount of water-soluble component and the amount of residual monomer are further reduced. That is, by using an acrylate salt of an amino group-containing azo compound, a water-absorbing resin having a water-soluble component amount of 20% by weight or less and a residual monomer amount reduced to 1,000 ppm or less is obtained. Can do.
[0043]
The amount of the foaming agent used relative to the monomer may be set according to the combination of the monomer and the foaming agent, and is not particularly limited, but is 0.001 with respect to 100 parts by weight of the monomer. More preferably within the range of 10 to 10 parts by weight. When the amount of the foaming agent used is out of the above range, the resulting water-absorbent resin may have insufficient water absorption characteristics.
[0044]
Moreover, the average particle diameter of the foaming agent present in a dispersed state during polymerization in the monomer aqueous solution is preferably in the range of 1 μm to 500 μm. By setting the average particle diameter of the foaming agent within the above range, the average pore diameter of the water absorbent resin can be adjusted within the range of 10 μm to 1,000 μm, and the water absorption characteristics of the water absorbent resin (for example, aqueous Liquid diffusivity, water absorption speed, etc.) can be improved. That is, by setting the average particle diameter of the foaming agent, the average pore diameter of the water absorbent resin can be set within a desired range.
[0045]
When the average particle diameter of the foaming agent is smaller than 1 μm, foaming is insufficient, and the average pore diameter of the water absorbent resin cannot be adjusted within a desired range, which is not preferable. On the other hand, when the average particle diameter of the foaming agent is larger than 500 μm, the average pore diameter of the water absorbent resin cannot be adjusted within a desired range. Moreover, since the gel strength of the water-absorbent resin obtained falls and the amount of water-soluble components increases, it is not preferable. In addition, the average particle diameter of the foaming agent in the monomer aqueous solution can be easily measured by using a laser type particle size distribution meter.
[0046]
Specific examples of the foaming agent precursor when the foaming agent is an inorganic compound include calcium oxide and magnesium oxide.
[0047]
The foaming agent precursor when the foaming agent is an acrylate salt of an amino group-containing azo compound is a hydrochloride salt of an amino group-containing azo compound, and specifically, for example, 2,2′-azobis (2- Methyl-N-phenylpropionamidine) dihydrochloride, 2,2′-azobis [N- (4-chlorophenyl) -2-methyl-propionamidine] dihydrochloride, 2,2′-azobis [N- (4- Hydroxyphenyl) -2-methylpropionamidine] dihydrochloride, 2,2′-azobis [2-methyl-N- (phenylmethyl) -propionamidine] dihydrochloride, 2,2′-azobis [2-methyl- N- (2-propenyl) propionamidine] dihydrochloride, 2,2′-azobis (2-methylpropionamidine) dihydrochloride, 2,2′-azobis [N- (2-hydroxyethyl) -2-me Cyl-propionamidine] dihydrochloride, 2,2′-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (2-imidazoline) -2-yl) propane] dihydrochloride, 2,2′-azobis- [2- (4,5,6,7-tetrahydro-1H-1,3-diazepin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (5-hydroxy-3,4,5) , 6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, etc. Can be mentioned. The hydrochlorides of these amino group-containing azo compounds are thermal decomposition azo polymerization initiators.
[0048]
The conditions for preparing the acrylate of the amino group-containing azo compound by reacting the hydrochloride of the amino group-containing azo compound with the acrylate are not particularly limited, but the following conditions are preferred. And these conditions are set arbitrarily, and the pore diameter of the resulting water-absorbent resin may be adjusted to a desired size by appropriately adjusting the particle diameter at the time of dispersion of the acrylate of the amino group-containing azo compound. .
[0049]
That is, the preparation temperature is preferably −10 ° C. to 50 ° C., and more preferably 0 ° C. to 40 ° C. Further, the acrylate is more preferably an alkali metal acrylate, and more preferably sodium acrylate. The neutralization rate of the acrylate is preferably 50 mol% or more, more preferably 70 mol% or more. And the density | concentration of the acrylate in monomer aqueous solution has the preferable inside of the range of 20 weight%-saturation concentration, and the inside of the range of 25 weight%-saturation concentration is more preferable.
[0050]
Moreover, when preparing the acrylic acid salt of an amino group-containing azo compound, it is preferable to stir the aqueous monomer solution. Then, an acrylic acid salt of an amino group-containing azo compound having a substantially uniform particle diameter is prepared in a short time by stirring the monomer aqueous solution preferably within a range of 10 rpm or more, more preferably 20 rpm to 10,000 rpm. can do. The prepared acrylate of an amino group-containing azo compound may be used as it is for the polymerization of the monomer, and it is not necessary to isolate it once.
[0051]
Examples of a method for preparing an amino group-containing azo compound acrylate salt in an aqueous monomer solution, that is, a method for dispersing the amino group-containing azo compound acrylate salt in an aqueous monomer solution include, for example, the following methods: Can be mentioned. That is, after preparing an acrylate salt of an amino group-containing azo compound by adding a hydrochloride salt of an amino group-containing azo compound to an acrylate salt with a neutralization rate of 100%, A method of obtaining a monomer aqueous solution by mixing a monomer such as a cross-linking agent and, if necessary, a solvent; a hydrochloride of an amino group-containing azo compound in a monomer aqueous solution prepared in advance; and Examples include a method of preparing an aqueous monomer solution in which an acrylic acid salt of an amino group-containing azo compound is dispersed by adding an acrylic acid salt as necessary. Among these methods, the latter method is preferable because an acrylate salt of an amino group-containing azo compound can be obtained more efficiently and the particle diameter becomes more uniform. In addition, after preparing an acrylate salt of an amino group-containing azo compound, the monomer in the aqueous monomer solution can be adjusted to a desired concentration by adding a solvent such as water to the aqueous monomer solution. Good.
[0052]
The water-containing gel containing bubbles is formed by dispersing the inert gas such as nitrogen, carbon dioxide, argon, helium, air, etc., which is inert to the polymerization reaction, in the monomer aqueous solution. It can also be obtained by polymerizing the monomer. Since the dispersed inert gas gas has no fear of inhibiting the polymerization of the monomer, a water-absorbing resin excellent in water-absorbing performance can be obtained. Moreover, by using together the surfactant etc. which are mentioned later, it is easy to adjust the magnitude | size and distribution of the bubble disperse | distributed inside, and a desired water absorbing resin can be obtained.
[0053]
Inert gas bubbles can be dispersed in the monomer aqueous solution by introducing an inert gas into the monomer aqueous solution, stirring the monomer aqueous solution at a high speed, and adding a blowing agent in advance. And the like. Moreover, you may disperse | distribute the bubble of an inert gas in monomer aqueous solution combining these methods. Examples of the method of strongly stirring at high speed include a method of stirring strongly with a stirrer and a stirring blade, a method of stirring strongly with a high speed homogenizer and an ultrasonic homogenizer, and the like.
[0054]
The volume of the monomer aqueous solution in which the bubbles of the inert gas are dispersed is preferably 1.02 times or more, and 1.08 times or more with respect to the volume of the non-dispersed monomer aqueous solution. More preferably, it is 1.11 times or more, more preferably 1.2 times or more.
[0055]
Even in the polymerization reaction operation under stirring conventionally performed, bubbles may be mixed into the aqueous monomer solution, but according to the inventors' confirmation, even if bubbles are mixed in a normal operation, The resulting volume change is less than 1.01 times. The volume of the monomer aqueous solution in which the bubbles of the inert gas are dispersed changes by 1.02 times or more with respect to the volume of the monomer aqueous solution in the non-dispersed state. This is a result of the inclusion of bubbles, whereby a water absorbent resin with further improved water absorption performance can be obtained. The state in which the inert gas bubbles are dispersed in the aqueous monomer solution can be easily visually confirmed by a decrease in the transparency of the aqueous monomer solution. Furthermore, since the volume change of the monomer aqueous solution appears only by the change in the height of the draft line in the reaction vessel, the volume change can be easily confirmed.
[0056]
When dispersing the bubbles made of the inert gas in the monomer aqueous solution, it is preferable to use a surfactant in combination. By using a surfactant in combination, the bubbles can be stably dispersed. In addition, the bubble diameter and bubble distribution of the bubbles can be more easily controlled by the surfactant.
[0057]
Examples of the surfactant include anionic surfactants, nonionic surfactants, cationic surfactants, and zwitterionic surfactants. Specific examples of the anionic surfactant include fatty acid salts such as mixed fatty acid sodium soap, semi-cured bovine fatty acid sodium soap, sodium stearate soap, potassium oleate soap, sodium oleate soap, and castor oil potassium soap. Alkyl sulfonates such as sodium lauryl sulfate, ammonium lauryl sulfate, higher alcohol sodium sulfate, triethanolamine lauryl sulfate; alkyl benzene sulfonates such as sodium dodecylbenzene sulfonate; alkyl naphthalene sulfonates such as sodium alkyl naphthalene sulfonate; Alkylsulfosuccinates such as sodium dialkylsulfosuccinate; alkyldiphenylether disulfonates such as sodium alkyldiphenyletherdisulfonate; Alkyl phosphates such as potassium phosphate; polyoxyethylene alkyl such as sodium polyoxyethylene lauryl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl ether sulfate triethanolamine, sodium polyoxyethylene alkylphenyl ether sulfate (Or alkylallyl) sulfate ester salt; special reaction type anionic surfactant; special carboxylic acid type surfactant; sodium salt of β-naphthalenesulfonic acid formalin condensate, sodium salt of special aromatic sulfonic acid formalin condensate, etc. Naphthalene sulfonic acid formalin condensate; special polycarboxylic acid type polymer surfactant; polyoxyethylene alkyl phosphate ester and the like can be mentioned, but it is not particularly limited.
[0058]
Specific examples of the nonionic surfactant include polyoxyethylene such as polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, and polyoxyethylene higher alcohol ether. Polyoxyethylene alkylaryl ethers such as alkyl ethers and polyoxyethylene nonylphenyl ethers; polyoxyethylene derivatives; sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, sorbitan trioleate Acid, sorbitan sesquioleate, sorbitan fatty acid esters such as sorbitan distearate; polyoxyethylene sorbitan monora Polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate and other polyoxyethylene sorbitan fatty acid esters; tetra Polyoxyethylene sorbitol fatty acid esters such as oleic acid polyoxyethylene sorbitol; Glycerin fatty acid esters such as glycerol monostearate, glycerol monooleate, and self-emulsifying type glyrosele monostearate; Polyethylene glycol monolaurate, polyethylene glycol monostearate , Polyethylene glycol distearate, polyethylene glycol monooleate, etc. Polyoxyethylene fatty acid esters; polyoxyethylene alkylamine, polyoxyethylene hardened castor oil; but alkyl alkanol amides, but is not particularly limited.
[0059]
Specific examples of the cationic surfactant and the double-sided surfactant include alkylamine salts such as coconut amine acetate and stearylamine acetate; lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, cetyltrimethylammonium chloride, Quaternary ammonium salts such as stearyldimethylammonium chloride and alkylbenzyldimethylammonium chloride; alkylbetaines such as laurylbetaine, stearylbetaine, laurylcarboxymethylhydroxyethylimidazolinium betaine; amine oxides such as lauryldimethylamine oxide; However, it is not particularly limited.
[0060]
Further, as the surfactant, there is a fluorine-based surfactant. By using the fluorine-based surfactant, it is possible to stably disperse the bubbles of the inert gas in the monomer aqueous solution for a long time. In addition, it is easy to control the amount of bubbles and the bubble diameter. And the water-absorbing resin obtained is a foam, becomes porous, and has a high water absorption rate. The fluorosurfactant used in the present invention is not particularly limited, and there are various conventionally known fluorosurfactants. For example, the hydrogen of the lipophilic group of a general surfactant is replaced with fluorine. A perfluoroalkyl group having a particularly strong surface activity is preferable.
[0061]
When the hydrophilic group of the fluorosurfactant is changed, there are four types of anionic, nonionic, cationic and amphoteric types. In the case of a flooded group, a fluorocarbon chain having the same structure is often used. In addition, the carbon chain which is a flooded group may be linear or branched. Specific examples of the fluorosurfactant include fluoroalkyl (C ₂ ~ C _Ten ) Carboxylic acid, disodium N-perfluorooctylsulfonyl glutamate, 3- [fluoroalkyl (C ₆ ~ C ₁₁ ) Oxy] -1-alkyl (C _Three ~ C _Four ) Sodium sulfonate, 3- [ω-fluoroalkanoyl (C ₆ ~ C ₈ ) -N-ethylamino] -1-propanesulfonic acid sodium, N- [3- (perfluorooctylsulfonamido) propyl] -N, N′-dimethyl-N-carboxymethyleneammonium betaine, fluoroalkyl (C ₁₁ ~ C ₂₀ ) Carboxylic acid, perfluoroalkylcarboxylic acid (C ₇ ~ C ₁₃ ), Perfluorooctylsulfonic acid diethanolamide, perfluoroalkyl (C _Four ~ C ₁₂ ) Sulfonate (Li, K, Na), N-propyl-N- (2-hydroxyethyl) perfluorooctylsulfonamide, perfluoroalkyl (C ₆ ~ C _Ten ) Sulfonamidopropyltrimethylammonium salt, perfluoroalkyl (C ₆ ~ C _Ten ) -N-ethylsulfonylglycine salt (K), bis (N-perfluorooctylsulfonyl-N-ethylaminoethyl) phosphate, monoperfluoroalkyl (C ₆ ~ C ₁₆ ) Ethyl phosphate ester, perfluoroalkyl quaternary ammonium iodide (trade name; Florard FC-135, manufactured by Sumitomo 3M Limited, cationic fluorosurfactant), perfluoroalkyl alkoxylate (trade name; Fluorard FC- 171, manufactured by Sumitomo 3M Limited, nonionic fluorine-based surfactant), perfluoroalkylsulfonic acid potassium salt (trade name: Florard FC-95 and Florard FC-98, manufactured by Sumitomo 3M Limited, anionic fluorine-based surfactant Agent) and the like, but are not particularly limited. These surfactants may be used alone or in combination of two or more.
[0062]
The amount of these surfactants used is preferably in the range of 0.0001 to 10 parts by weight per 100 parts by weight of the total amount of the water-soluble unsaturated monomer and the water-soluble crosslinking monomer, More preferably, it is in the range of 0.0003 to 5 parts by weight. When the amount of the surfactant used is less than 0.0001 parts by weight, the water absorption rate may not be sufficiently improved, which is not preferable. On the other hand, if the amount exceeds 10 parts by weight, the effect corresponding to the amount added may not be achieved, which is not preferable because it is not economical.
[0063]
Conventionally, it is known to use a surfactant in aqueous solution polymerization, but such a known technique does not improve the water absorption rate at all.
[0064]
The polymerization method for polymerizing the monomer component is not particularly limited, and various conventionally known polymerization methods such as bulk polymerization, precipitation polymerization, aqueous solution polymerization or reverse phase suspension polymerization can be employed. From the viewpoint of improving the water absorption characteristics of the water-absorbing resin obtained and facilitating control of polymerization, it is preferable to perform aqueous solution polymerization or reverse phase suspension polymerization using the monomer component as an aqueous solution.
[0065]
As the above aqueous solution polymerization method, a thin film polymerization that forms a thin film on a drive belt; a method in which an aqueous solution of a monomer component is put into a predetermined mold and polymerization; a stirring blade having a predetermined shape is provided Examples include a polymerization method in which an aqueous solution of a monomer component is polymerized using a mixer such as a kneader as a polymerization apparatus, and the generated hydrous gel is subdivided by the shearing force of the stirring blade.
[0066]
Among these polymerization methods, the latter polymerization method is more preferable because a particulate water-containing gel is obtained when the polymerization reaction is completed. Further, it is preferable that the monomer is allowed to stand for polymerization without stirring during the polymerization reaction. Further, when the above ethylenically unsaturated monomer is polymerized in an aqueous solution, any one of continuous polymerization or batch polymerization may be employed, and any of normal pressure, reduced pressure, and pressurized pressure may be employed. You may implement under the pressure of. The polymerization reaction is preferably performed under a stream of inert gas such as nitrogen, helium, argon, carbon dioxide.
[0067]
Moreover, as said reverse phase suspension polymerization method, the method of suspending and polymerizing the aqueous solution of a monomer component in a hydrophobic organic solvent in presence of a dispersing agent, etc. are mentioned, for example. By employing the reverse phase suspension polymerization method, a spherical (particulate) hydrous gel is obtained when the polymerization reaction is completed.
[0068]
As a method of pulverizing the hydrogel, a rotary pulverizer equipped with a fixed blade and a rotating rotary blade is used in a cylindrical pulverization chamber, and is crushed by shearing between the fixed blade and the rotary blade. To do. In the rotary crusher, the rotary blade extends in the vertical direction and is substantially parallel to the blade of the fixed blade, and the rotation axis of the rotary blade is also vertical. In the rotary crusher, one to four fixed blades are provided along the circumferential direction on the inner wall of the crushing chamber, while the rotary blades extend radially outward at equal intervals from the rotating shaft. 2 to 5 are provided.
[0069]
In the above-described rotary crusher, the hydrogel introduced between the rotary blades is caused by the centrifugal force of the rotating rotary blades so that the hydrogels are deadweight, and the fixed blades and the rotary blades are radially outward of the rotary blades. Extruded in between. The hydrated gel thus extruded is cut and crushed by shearing between the fixed blade and the rotary blade. As a result, in the above-mentioned rotary crusher, the force is applied almost uniformly to the entire hydrogel by centrifugal force and moves outward in the radial direction. The air bubbles are reduced from being crushed. From this, the said hydrogel can be crushed, suppressing the reduction | decrease of the bubble contained in a hydrogel, ie, the bubble in the hydrogel after crushing is hold | maintained 20% or more. Moreover, since the said water-containing gel has a crosslinked structure, it has predetermined | prescribed hardness and viscosity larger than the conventional water-soluble polymer gel, and it adheres to a rotary crusher, a fixed blade, and a rotary blade. Therefore, it can be easily crushed by a rotary crusher.
[0070]
The crushing time, that is, the residence time during which the hydrogel stays in the rotary crusher is the amount of the hydrogel input, the size of the fixed blade and the rotary blade, the rotational speed of the rotary blade, or the hydrogel after crushing. Although it can set suitably according to a magnitude | size, 1 second or more and less than 3 minutes are preferable, and 5 seconds or more and less than 1 minute are more preferable. When the crushing time is shorter than 1 second, the hydrated gel is not sufficiently crushed, which is not preferable. In addition, when the pulverization time is 3 minutes or more, bubbles contained in the hydrated gel are crushed or the hydrated gel after pulverization becomes too fine.
[0071]
The size of the particle size of the hydrogel after pulverization may be such that it can be sufficiently dried to the inside by a drying step, preferably in the range of 0.1 mm to 30 mm, and more preferably in the range of 1 mm to 15 mm. . When the particle size of the hydrogel after pulverization is smaller than 0.1 mm, clogging is likely to occur during drying of the water-absorbent resin, the drying efficiency is reduced, and internal bubbles are crushed. It is not preferable. On the other hand, when the particle size of the hydrogel after crushing is larger than 30 mm, it is difficult to sufficiently dry the water-absorbent resin to the inside, which is not preferable. In addition, when the water-containing gel obtained by the aqueous solution polymerization method is a lump, it is more preferable to crush the water-containing gel into particles having a predetermined particle diameter.
[0072]
The crushed water-containing gel is discharged from the roaster of the rotary crusher. Since the diameter of the rooster is generally in the range of 1 mm to 50 mm, the hydrogel that has been crushed is reduced in tackiness due to cross-linking, and is sucked under reduced pressure to clog the hydrogel into the rooster. It can discharge without.
[0073]
In addition, by crushing the hydrogel using such a rotary crusher, the hydrogel is not moved by pressing or a screw like a conventional meat chopper, and the fixed blade and the rotary blade are separated by centrifugal force. Since the water-containing gel moves during the period, reduction of bubbles in the water-containing gel due to pressing and kneading is suppressed. Further, since the hydrogel sandwiched between the fixed blade and the rotating rotary blade is cut by shearing between the fixed blade and the rotary blade, the pressing force on the entire hydrogel can be reduced, and the air bubbles can be reduced by pressing. Can be reduced from being crushed. Thereby, since 20% or more of the bubbles contained in the water-containing gel are retained, the water-absorbing property of the obtained water-absorbent resin is further improved.
[0074]
In addition, conventional screw-type extruders such as meat choppers; (machines) by means of pressure kneaders, international mixers, kneaders such as Banbury mixers etc. A porous water-absorbent resin having a high bubble retention rate that could not be realized can be obtained.
[0075]
In the method of the present invention, since the hydrogel can be continuously and efficiently crushed using a fixed blade and a rotating blade, the crushing efficiency is higher than in the case of using the scissors as in the past and crushed by hand. Can be improved, and productivity can be improved.
[0076]
Further, secondary crosslinking (surface crosslinking) may be introduced into the water-absorbent resin by adding a surface crosslinking agent. The surface cross-linking agent may be any compound that has a plurality of reactive groups and reacts with a functional group such as a carboxyl group that the water-absorbent resin has, and generally employs a known surface cross-linking agent used for this purpose. be able to.
[0077]
Specific examples of the surface cross-linking agent include (poly) ethylene glycol, diethylene glycol, (poly) propylene glycol, triethylene glycol, tetraethylene glycol, 1,3-propanediol, dipropylene glycol, 2, 2,4-trimethyl-1,3-pentanediol, (poly) glycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1 , 2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol, sorbitol, polyvinyl alcohol, group Polyhydric alcohols such as course, mannitol, sucrose and glucose; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, (poly) propylene glycol di Polyvalent epoxy compounds such as glycidyl ether; polyvalent amine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine and polyethyleneimine; polyvalent amine compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate Isocyanate compound; polyvalent oxazoline compound such as 1,2-ethylenebisoxazoline; 1,3-dioxolan-2-o 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-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-dioxan-2-one, Alkylene carbonate compounds such as 4,6-dimethyl-1,3-dioxan-2-one, 1,3-dioxopan-2-one; epichlorohydrin, epibromohydrin, α-methylepichlorohydrin, etc. Haloepoxy compounds; polyvalent metal compounds such as hydroxides and chlorides of polyvalent metals such as zinc, calcium, magnesium, aluminum, iron and zirconium; Not. These surface cross-linking agents may be used alone or in combination of two or more.
[0078]
By introducing surface crosslinking into the water absorbent resin using a surface crosslinking agent, the water absorption magnification under pressure of the water absorbent resin is further improved. In addition, the amount of a component that elutes into the aqueous liquid when contacted with the aqueous liquid, that is, a so-called water-soluble component can be reduced. The amount of the surface cross-linking agent used, the processing temperature, and the processing time may be appropriately set according to the type and combination of the water-absorbent resin and the surface cross-linking agent to be used, the desired degree of surface cross-linking, etc., and are particularly limited. It is not something.
[0079]
As described above, the method for producing the water-absorbent resin of the present invention can be crushed without crushing the bubbles contained in the water-containing gel. Furthermore, since the hydrated gel after pulverization has air bubbles retained therein, it has excellent water absorption characteristics such as water absorption capacity, water absorption speed, water absorption capacity under pressure, and the amount of water-soluble components and the amount of residual monomer. It is possible to industrially obtain a porous and granular water-absorbing resin with a reduced amount of water easily and in large quantities.
[0080]
The water-absorbent resin obtained by the production method of the present invention includes, for example, sanitary materials such as paper diapers, sanitary napkins, tampons, incontinence pads, wound protection materials, wound healing materials; absorbent articles such as urine for pets; Civil engineering and construction materials such as water retention materials, water-stopping materials, packing materials, gel water sacs, etc .; food products such as food freshness-keeping materials, food drip absorbent materials, cold insulation materials; oil-water separators, dew condensation water-absorbing sheets, Various industrial articles such as solidified materials; agricultural and horticultural articles such as agricultural and horticultural water retaining materials; and the like can be suitably used.
[0081]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited at all by these. Various performances of the water absorbent resin were measured by the following methods. Further, “parts” described in Examples and Comparative Examples indicates “parts by weight”.
[0082]
(A) Water absorption magnification under no pressure
About 0.2 g of the water-absorbing resin was accurately weighed, put into a 5 cm square non-woven tea bag, and sealed by heat sealing. This tea bag was immersed in artificial urine at room temperature. After 1 hour, the tea bag was pulled up and drained at 1300 rpm for 3 minutes using a centrifuge. ₁ (G) was measured. Separately, the same operation is performed without sealing the water-absorbing resin in the tea bag, and the weight W of the tea bag at that time ₀ (G) was determined as a blank. The water absorption magnification is
[0083]
[Expression 1]

Calculated based on
[0084]
The composition of the artificial urine and the blending amount thereof are as follows.
[0085]
Composition of artificial urine
Sodium sulfate 0.200%
Potassium chloride 0.200%
Magnesium chloride hexahydrate 0.050%
Calcium chloride dihydrate 0.025%
Ammonium dihydrogen phosphate 0.035%
Ammonium hydrogen phosphate 0.015%
99.475% deionized water
(B) Water-soluble component amount of the water-absorbent resin
0.5 g of the water-absorbent resin was dispersed in 1,000 ml of deionized water, stirred for 16 hours, and then filtered through filter paper. And the amount (%) of water-soluble components was calculated | required by colloid titrating the obtained filtrate.
[0086]
(C) Residual monomer amount of water absorbent resin
After adding 100 ml of deionized water to a beaker having a capacity of 200 ml, 1.0 g of a water-absorbing resin was added with stirring to gel all the deionized water. After 1 hour, the gel was contracted by adding 5 ml of phosphoric acid aqueous solution to the obtained gel. The shrunken gel was filtered through a filter paper with stirring, and the filtrate, that is, the water generated by the shrinkage was analyzed using high performance liquid chromatography.
[0087]
On the other hand, the same analysis was performed using a monomer aqueous solution having a known concentration as a standard solution, and a calibration curve was obtained. Then, this calibration curve was set as an external standard, and the residual monomer amount (ppm) of the water-absorbent resin was determined in consideration of the dilution ratio of the filtrate. The residual monomer amount is a conversion value with respect to the solid content of the water absorbent resin.
[0088]
(D) Water absorption speed
A water-absorbing resin 1.0 g was put in a bottomed cylindrical polypropylene cup having an inner diameter of 50 mm and a height of 70 mm. Next, 28 g of physiological saline was poured into the cup, and the physiological saline was uniformly absorbed by the water-absorbent resin. Then, the time from when the physiological saline was poured until the physiological saline was all gelled and the physiological saline was completely absorbed by the water-absorbent resin and became invisible was measured. This measurement was repeated three times, and the average value of these was taken as the water absorption rate (seconds).
[0089]
(E) Water absorption capacity under pressure of water absorbent resin
First, a measurement apparatus used for measuring the water absorption magnification under pressure will be briefly described below with reference to FIG.
[0090]
As shown in FIG. 4, the measuring device includes a balance 1, a container 2 having a predetermined capacity placed on the balance 1, an outside air suction pipe 3, a conduit 4 made of silicone resin, a glass filter 6, The measuring unit 5 is placed on the glass filter 6. The container 2 has an opening 2a at the top and an opening 2b at the side, and the outside air intake pipe 3 is fitted into the opening 2a, while the conduit 4 is attached to the opening 2b. It has been.
[0091]
The container 2 contains a predetermined amount of artificial urine 12. The lower end of the outside air intake pipe 3 is submerged in the artificial urine 12. The outside air suction pipe 3 is provided in order to keep the pressure in the container 2 at almost atmospheric pressure. The glass filter 6 is formed with a diameter of 55 mm. The container 2 and the glass filter 6 are communicated with each other by a conduit 4. Further, the glass filter 6 is fixed in position and height with respect to the container 2.
[0092]
The measurement unit 5 includes a filter paper 7, a support cylinder 9, a wire mesh 10 attached to the bottom of the support cylinder 9, and a weight 11. In the measuring unit 5, the filter paper 7 and the support cylinder 9 (that is, the wire mesh 10) are placed on the glass filter 6 in this order, and the weight 11 is placed inside the support cylinder 9, that is, on the wire mesh 10. It has become. The metal mesh 10 is made of stainless steel and has a mesh size of 400 (mesh size 38 μm). At the time of measurement, a predetermined amount and a predetermined particle diameter of the water-absorbing resin 15 are uniformly distributed on the wire mesh 10. Further, the height of the upper surface of the metal mesh 10, that is, the contact surface between the metal mesh 10 and the water absorbent resin 15 is set to be equal to the height of the lower end surface 3 a of the outside air intake pipe 3. The weight 11 is 50 g / cm with respect to the wire mesh 10, that is, the water absorbent resin 15. ² The weight is adjusted so that the load can be uniformly applied.
[0093]
The water absorption magnification under pressure was measured using the measuring apparatus having the above configuration. The measurement method will be described below.
[0094]
First, predetermined preparatory operations such as putting a predetermined amount of artificial urine 12 into the container 2; inserting the outside air suction pipe 3 into the container 2; Next, the filter paper 7 was placed on the glass filter 6. In parallel with this placement operation, 0.9 g of water-absorbing resin 15 was uniformly distributed inside the support cylinder 9, that is, on the wire mesh 10, and the weight 11 was placed on the water-absorbing resin 15. .
[0095]
Subsequently, the metal mesh 10, that is, the support cylinder 9 on which the water absorbent resin 15 and the weight 11 were placed was placed on the filter paper 7 so that the center portion thereof coincided with the center portion of the glass filter 6.
[0096]
The weight W of the artificial urine 12 absorbed by the water-absorbent resin 15 over time from the time when the support cylinder 9 is placed on the filter paper 7. ₂ (G) was measured using the balance 1. The same operation is performed without using the water absorbent resin 15, and the weight at that time, that is, the weight of the artificial urine 12 absorbed by, for example, the filter paper 7 other than the water absorbent resin 15 is measured using the balance 1. , Blank weight W _Three (G). And these weights W ₂ ・ W _Three From the following formula,
Water absorption capacity under pressure (g / g) = (weight W ₂ (g)-Weight W _Three (g)) / weight of water absorbent resin (g)
The water absorption capacity under pressure (g / g) was calculated.
[0097]
(F) Water-absorbent resin particle area, pore area, pore area ratio and retention rate
First, the hydrogel was crushed with scissors, a rotary crusher, and a meat chopper. Electron microscope (SEM) photography of particles in each water-absorbent resin obtained by drying and pulverizing the hydrogel after pulverization obtained by each pulverization method was performed at a magnification of 25 times. Next, it was assumed that the particles and pores of the water-absorbing resin obtained were elliptical, and the major axis and minor axis of the particles in the SEM photograph and the pores on the particle surface were measured with calipers. And the following formula:
Particle area (μm ² ) = Π / 4 (major diameter of particle / magnification of photograph) × (minor diameter of particle / magnification of photograph)
Pore area (μm ² ) = Π / 4 (major diameter of pore / magnification of photograph) × (minor diameter of pore / magnification of photograph)
Pore area ratio (%) = Σ (particle surface pore area) / Σ (particle area) × 100
Retention ratio (%) = (pore area ratio) / (pore area ratio when crushed with scissors) × 100
Thus, the area of the water-absorbent resin particles, the area of the pores, the pore area ratio, and the retention ratio were calculated.
[0098]
[Example 1]
Mix 83.2 parts of acrylic acid, 1662.8 parts of 37 wt% sodium acrylate aqueous solution, 5.5 parts of polyethylene glycol diacrylate (average number of moles of added ethylene oxide (EO) 8) and 654.5 parts of deionized water. Thus, an aqueous monomer solution having a neutralization ratio of acrylic acid of 85% and a monomer concentration of 30% by weight was prepared.
[0099]
While maintaining the monomer aqueous solution at a temperature of 24 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen in the monomer aqueous solution. Subsequently, 77 parts of a 10% by weight aqueous 2,2′-azobis (2-methylpropionamidine) dihydrochloride solution was added to the aqueous monomer solution with stirring.
[0100]
Three minutes after the start of stirring, the monomer aqueous solution to which 2,2′-azobis (2-methylpropionamidine) dihydrochloride was added became cloudy and a white fine particle solid having an average particle diameter of about 9 μm was formed. did. The fine particulate solid was 2,2′-azobis (2-methylpropionamidine) diacrylate as a foaming agent.
[0101]
Furthermore, 5 minutes after the start of stirring, 10.8 parts of a 10% by weight sodium persulfate aqueous solution and 0.5 part of a 1% by weight L-ascorbic acid aqueous solution as radical polymerization initiators were added while stirring in a nitrogen atmosphere. It added to the said monomer aqueous solution. The aqueous solution was sufficiently stirred and then allowed to stand.
[0102]
The polymerization reaction started 3 minutes after the addition of 10% by weight aqueous sodium persulfate solution and 1% by weight aqueous L-ascorbic acid solution. The polymerization reaction was carried out in a hot water bath while keeping the temperature of the aqueous solution following the temperature of the hot water bath. 26 minutes after the addition of the 10% by weight aqueous sodium persulfate solution, the temperature of the aqueous solution to which the aqueous sodium persulfate solution was added reached 97 ° C. Thereafter, the aqueous solution was allowed to stand for another 20 minutes while maintaining the temperature in the range of 70 ° C. to 90 ° C. to complete the polymerization reaction of the acrylate monomer. As a result, a water-containing gel having air bubbles, which is a porous crosslinked polymer, was obtained.
[0103]
Subsequently, the hydrogel was continuously crushed by the above-mentioned rotary crusher. The average residence time of the hydrogel in the rotary crusher during crushing, that is, the crushing time was about 0.25 minutes. The size of the hydrogel after pulverization was in the range of about 1 mm to 15 mm in particle diameter.
[0104]
The hydrogel after pulverization was dried at 160 ° C. for 1 hour by a circulating hot air dryer. Next, the dried water-containing gel is pulverized by a roll mill, and further passed through a sieve having a mesh size of 850 μm using a JIS standard sieve, and the water-absorbent resin of the present invention having a particle diameter remaining on the 150 μm sieve ( 1) was obtained. The results of measuring various performances of the obtained water-absorbent resin (1) of the present invention are shown in Table 1.
[0105]
Furthermore, SEM photography of the water-absorbent resin (1) was performed at a magnification of 25 times, and the major and minor diameters of the particles and the pores on the particle surface were measured with calipers. The pore area, pore area ratio, and retention rate were calculated. A SEM photograph of the water absorbent resin (1) is shown in FIG.
[0106]
[Comparative Example 1]
First, a hydrogel having bubbles was produced. That is, by performing the same operation and reaction as those of Example 1, a hydrogel having bubbles was obtained. Furthermore, the water-absorbing resin (1) for comparison was obtained by performing the same operation as in Example 1 except that the hydrogel was pulverized using a meat chopper having a rooster with a diameter of 8 mm. It took about 5 minutes to disintegrate. Table 1 shows the results obtained by measuring various performances of the comparative water absorbent resin (1) obtained.
[0107]
Furthermore, SEM photography of the comparative water-absorbing resin (1) was performed at a magnification of 25 times, and the major and minor diameters of the particles and the pores on the surface of the particles were measured with calipers. The particle area, the pore area, the pore area ratio, and the retention ratio of (1) were calculated. The SEM photograph of the comparative water absorbent resin (1) is shown in FIG.
[0108]
[Comparative Example 2]
First, a hydrogel having bubbles was produced. That is, by performing the same operation and reaction as those of Example 1, a hydrogel having bubbles was obtained. Further, the water-containing resin for comparison was obtained by performing the same operation as in Example 1 except that this hydrogel was crushed by scissors so that the particle diameter was within the range of about 1 mm to 5 mm. (2) was obtained. The crushing took about 30 minutes. Table 1 shows the results obtained by measuring various performances of the comparative water-absorbing resin (2).
[0109]
Furthermore, SEM photography of the comparative water-absorbing resin (2) was performed at a magnification of 25 times, and the major and minor diameters of the particles and the pores on the particle surface were measured with calipers, whereby the comparative water-absorbing resin. The area of the resin (2) particles, the area of the pores, the pore area ratio, and the retention ratio were calculated. The SEM photograph of the comparative water absorbent resin (2) is shown in FIG.
[0110]
[Example 2]
A monomer aqueous solution was prepared by mixing 27 parts of acrylic acid, 285 parts of a 37 wt% aqueous sodium acrylate solution, 1.1 parts of polyethylene glycol diacrylate (average EO addition mole number 8), and 117.6 parts of deionized water. It was adjusted. The monomer aqueous solution is an aqueous solution having a neutralization ratio of acrylic acid of 75% and a monomer concentration of 31% by weight.
[0111]
While maintaining the monomer aqueous solution at 16 ° C., nitrogen gas was blown into the liquid to remove dissolved oxygen in the monomer aqueous solution. Next, 8.9 parts of a 1% by weight aqueous solution of polyoxyethylene sorbitan monostearate, a surfactant having a hydrophilo-lypophile balance (HLB) of 14.9, was added with stirring.
[0112]
Next, 2.1 parts of a 10 wt% sodium persulfate aqueous solution and 0.1 part of a 1 wt% L-ascorbic acid aqueous solution as radical polymerization initiators were added to the monomer aqueous solution while stirring in a nitrogen atmosphere. The aqueous solution was sufficiently stirred and then allowed to stand.
[0113]
Four minutes after the addition of the 10 wt% sodium persulfate aqueous solution and the 1 wt% L-ascorbic acid aqueous solution, the monomer aqueous solution started to become cloudy and the polymerization reaction was started. Was added. The polymerization reaction was carried out in a hot water bath while keeping the temperature of the aqueous solution following the temperature of the hot water bath. 37 minutes after adding 10 wt% sodium persulfate to the aqueous solution, the temperature of the aqueous solution reached about 93 ° C.
[0114]
Thereafter, the monomer aqueous solution was allowed to stand still for 20 minutes while maintaining the temperature within the range of 70 ° C. to 90 ° C., thereby completing the polymerization reaction of the acrylate monomer. As a result, a water-containing gel having air bubbles, which is a porous crosslinked polymer, was obtained.
[0115]
Furthermore, the water-containing gel was continuously crushed by the above-mentioned rotary crusher. The average residence time of the hydrogel in the rotary crusher during crushing, that is, the crushing time was about 0.16 minutes. The size of the hydrogel after pulverization is about 2 mm-15
It was in the range of mm.
[0116]
The hydrogel after pulverization was dried at 160 ° C. for 1 hour by a circulating hot air dryer. Next, the dried water-containing gel is pulverized by a roll mill, and further passed through a sieve having a mesh size of 850 μm using a JIS standard sieve, and the water-absorbent resin of the present invention having a particle diameter remaining on the 150 μm sieve ( 2) was obtained. The results of measuring various performances of the obtained water-absorbent resin (2) of the present invention are shown in Table 1.
[0117]
[Comparative Example 3]
First, a hydrogel having bubbles inside was produced. That is, by performing the same operations and reactions as those in Example 2, a hydrogel having bubbles was obtained. Furthermore, the water-absorbing resin (3) for comparison was obtained by performing the same operation as in Example 2 except that the hydrogel was crushed using a meat chopper having a rooster with a diameter of 8 mm. It took about 4 minutes to disintegrate. Table 1 shows the results obtained by measuring various performances of the comparative water-absorbing resin (3).
[0118]
[Comparative Example 4]
First, a hydrogel having bubbles inside was produced. That is, by performing the same operations and reactions as those in Example 2, a hydrogel having bubbles was obtained. Further, the water-containing resin for comparison was obtained by performing the same operation as in Example 1 except that this hydrogel was crushed by scissors so that the particle diameter was within the range of about 1 mm to 5 mm. (4) was obtained. The crushing took about 30 minutes. Table 1 shows the results obtained by measuring various performances of the comparative water-absorbing resin (4).
[0119]
Example 3
First, secondary crosslinking treatment was performed on the water-absorbent resin (1) of the present invention obtained in Example 1. That is, the treatment liquid for secondary crosslinking treatment was 0.05 part of ethylene glycol diglycidyl ether, 0.5 part of lactic acid, 0.02 part of polyoxyethylene sorbitan monostearate, 0.75 part of isopropyl alcohol and 3 parts of water. Was adjusted by mixing.
[0120]
Next, 100 parts of the water-absorbent resin (1) of the present invention obtained in Example 1 was mixed with the treatment liquid, and the resulting mixture was heat-treated at 195 ° C. for 30 minutes to obtain the water-absorbent resin of the present invention. (3) was obtained. Table 1 shows the results obtained by measuring various performances of the obtained water-absorbent resin (3) of the present invention.
[0121]
Example 4
First, secondary crosslinking treatment was performed on the water absorbent resin (2) of the present invention obtained in Example 2. That is, the treatment liquid for secondary crosslinking treatment was adjusted by mixing 1 part of glycerin, 1.75 parts of ethyl alcohol and 3 parts of water.
[0122]
Next, 100 parts of the water-absorbent resin (2) of the present invention obtained in Example 2 was mixed with the treatment liquid, and the resulting mixture was heat-treated at 195 ° C. for 30 minutes to obtain the water-absorbent resin of the present invention. (4) was obtained. Table 1 shows the results obtained by measuring various performances of the obtained water-absorbent resin (4) of the present invention.
[0123]
Example 5
27.0 parts of acrylic acid, 285.0 parts of 37% by weight sodium acrylate aqueous solution, 1.1 parts of polyethylene glycol diacrylate (average EO addition mole number 8), fluorine-based cationic surfactant (trade name; Fluorard FC- 135, manufactured by Sumitomo 3M Limited) and an aqueous monomer solution were prepared by mixing 0.013 parts and 117.6 parts deionized water.
[0124]
While the monomer aqueous solution is vigorously stirred at a high speed (3,000 rpm) with a high-speed homodisperse, nitrogen gas is blown into the liquid to expel dissolved oxygen in the monomer aqueous solution, and from the nitrogen into the monomer aqueous solution. The resulting bubbles were dispersed. When nitrogen gas is uniformly dispersed in the monomer aqueous solution and its volume is increased by 1.25 times, 2.1 parts of 10% by weight sodium persulfate aqueous solution and 10% by weight of sulfurous acid are added under high-speed vigorous stirring. 2.1 parts of an aqueous sodium hydride solution was added, and the polymerization reaction was immediately started. With the bubbles dispersed in the aqueous monomer solution, the temperature was set within the range of 25 ° C. to 75 ° C. and the polymerization was allowed to stand for 2 hours. As a result, a hydrous gel in which bubbles were dispersed was obtained.
[0125]
Subsequently, the hydrogel was continuously crushed by the above-mentioned rotary crusher. The average residence time of the hydrogel in the rotary crusher during crushing, that is, the crushing time was about 0.16 minutes. The size of the hydrogel after pulverization was in the range of about 2 mm to 15 mm in particle diameter.
[0126]
The hydrogel after pulverization was dried at 160 ° C. for 1 hour by a circulating hot air dryer. Next, the dried water-containing gel is pulverized by a roll mill, and further passed through a sieve having a mesh size of 850 μm by a JIS standard sieve, and the water-absorbent resin of the present invention having a particle diameter remaining on the 150 μm sieve ( 5) was obtained. Table 1 shows the results obtained by measuring various performances of the water absorbent resin (5) of the present invention obtained.
[0127]
[Comparative Example 5]
First, a hydrogel having bubbles inside was produced. That is, by performing the same operations and reactions as those in Example 5, a hydrogel having bubbles was obtained. Further, a comparative water-absorbent resin (5) was obtained in the same manner as in Example 5 except that the hydrogel was pulverized using a meat chopper having a rooster with a diameter of 8 mm. It took about 5 minutes to disintegrate. Table 1 shows the results of measuring various performances of the comparative water-absorbing resin (5).
[0128]
[Comparative Example 6]
First, a hydrogel having bubbles inside was produced. That is, by performing the same operations and reactions as those in Example 5, a hydrogel having bubbles was obtained. Further, a comparative water-absorbent resin (6) was obtained by performing the same operation as in Example 5 except that the hydrogel was crushed using a meat chopper having a rooster with a diameter of 8 mm. The crushing took about 30 minutes. Table 1 shows the results obtained by measuring various performances of the obtained comparative water-absorbent resin (6).
[0129]
[Table 1]

[0130]
[Table 2]

As is apparent from the results of Examples 1 to 5 described in Table 1, the water-absorbent resin obtained by the production method according to the present invention sufficiently retains bubbles, so that no pressure is applied. It is understood that the water absorption properties such as the water absorption rate, the water absorption rate, and the water absorption rate under pressure are excellent, and the water-soluble component amount and the residual monomer amount are reduced. Moreover, in this invention, from the comparison with the said Examples 1-5 and Comparative Examples 2 and 4, it can aim at the significant reduction of crushing time and simplification of crushing operation, and industrial production is possible. I understand.
[0131]
【The invention's effect】
The present invention Pertaining to As described above, the method for producing a water-absorbent resin is a method in which crushing is performed by shearing the hydrogel with a fixed blade and a rotating blade.
[0132]
Therefore, in the above method, since the hydrogel is crushed by shearing, it is possible to suppress air bubbles from being crushed during the pulverization as in the related art. Moreover, in the said method, since a hydrogel can be crushed continuously, crushing efficiency can be improved and productivity can be improved, suppressing the reduction | decrease of a bubble. As a result, the above method is excellent in water absorption characteristics such as water absorption capacity, water absorption speed and water absorption capacity under pressure, and a large amount of water-absorbing resin in which the amount of water-soluble components and residual monomers is reduced can be easily and The effect that it can be obtained is produced.
[0133]
Also, The present invention Pertaining to As described above, the method for producing a water absorbent resin is a method in which crushing is performed by extruding a hydrous gel between a fixed blade and a rotary blade by a centrifugal force generated by a rotary blade having a vertical rotating shaft. .
[0134]
Thus, in the above method, the pulverization is performed by moving the hydrous gel containing bubbles inside by centrifugal force and shearing by the fixed blade and the rotary blade. Since the force in the moving direction is uniformly applied to the hydrated gel as compared with the movement due to the above, it can be crushed by shearing while suppressing the bubbles in the hydrated gel from being crushed. Therefore, in the above method, the reduction of bubbles is suppressed, and a porous water-absorbent resin due to bubbles can be obtained stably and simply. Therefore, the water absorption capacity under no pressure, the water absorption speed, and the water absorption under pressure. There is an effect that a water-absorbing resin excellent in water-absorbing properties such as magnification can be industrially obtained in large quantities.
[0135]
The present invention Pertaining to As described above, the method for producing a water-absorbent resin can suppress the reduction of the above-mentioned water-containing gel obtained by polymerizing an ethylenically unsaturated monomer so as to contain bubbles in the presence of a crosslinking agent, for example, In this method, the bubbles are crushed so that 20% or more is maintained.
[0136]
Thereby, in the said method, it can crush, suppressing crushing of an internal bubble by crushing so that the reduction | decrease of the bubble which a hydrogel has inside may be suppressed. Therefore, since the hydrogel after pulverization has air bubbles inside, it has excellent water absorption characteristics such as water absorption capacity under no pressure, water absorption speed and water absorption capacity under pressure, and the amount of water-soluble components. In addition, it is possible to stably obtain a water-absorbent resin with a reduced amount of residual monomer.
[0137]
The present invention Pertaining to As described above, the method for producing the water-absorbent resin is such that the water-containing gel is obtained by dispersing the inert gas bubbles in an aqueous solution containing the ethylenically unsaturated monomer and the crosslinking agent. And a method obtained by polymerizing a crosslinking agent.
[0138]
Thereby, in the above method, since the inert gas does not inhibit the polymerization reaction, a porous water-containing gel having bubbles inside is stably obtained, the water absorption capacity under no pressure, the water absorption speed, and the water absorption capacity under pressure. The water-absorbing resin excellent in water absorption characteristics such as the above can be obtained stably.
[0139]
The present invention Pertaining to As described above, the method for producing the water-absorbent resin is a method in which the surface vicinity of the particulate matter obtained by crushing the hydrogel is secondarily crosslinked.
[0140]
Thereby, in the above method, the water absorption capacity under pressure of the water-absorbent resin is further improved by secondary crosslinking, and the component that elutes into the aqueous liquid when it comes into contact with the aqueous liquid, that is, the soluble component of water There is an effect that a water-absorbing resin in which the amount of the residual monomer and the amount of residual monomer are reduced by secondary crosslinking can be obtained.
[Brief description of the drawings]
FIG. 1 is a drawing-substituting photograph showing the particle structure of the water-absorbent resin described in Example 1 with an electron micrograph (25 times) in the method for producing a water-absorbent resin of the present invention.
FIG. 2 is a drawing-substituting photograph showing the particle structure of a comparative water-absorbing resin described in Comparative Example 1 with an electron micrograph (25 ×) for each example of the production method.
FIG. 3 is a drawing-substituting photograph showing the particle structure of the comparative water-absorbing resin described in Comparative Example 2 with an electron micrograph (25 times) with respect to each example of the production method.
FIG. 4 is a schematic cross-sectional view of a measuring apparatus used for measuring the water absorption magnification under pressure of a water absorbent resin in the manufacturing method.
[Explanation of symbols]
1 Balance
2 containers
3 Outside air intake pipe
4 conduit
5 Measurement section
6 Glass filter
7 Filter paper
9 Support cylinder
10 Wire mesh
11 Weight
12 Artificial urine
15 Water-absorbing resin

Claims (6)

A hydrogel obtained by polymerizing an ethylenically unsaturated monomer so as to contain bubbles in the presence of a crosslinking agent is provided with a fixed blade and a rotary blade , and the residence time of the hydrogel is 1 second or more 3 A method for producing a water-absorbent resin, comprising: crushing by shearing with a rotary crusher that is less than a minute , and then drying .   The method for producing a water-absorbent resin according to claim 1, wherein the crushing is performed by extruding the hydrous gel between the fixed blade and the rotary blade by a centrifugal force generated by a rotary blade having a vertical rotating shaft. . The method for producing a water-absorbent resin according to claim 1 or 2, wherein the water- containing resin is crushed so that a decrease in bubbles contained in the hydrous gel is suppressed. The method for producing a water-absorbent resin according to any one of claims 1 to 3, wherein the hydrated gel after crushing retains 20% or more of bubbles. Hydrogel containing the bubbles, see contains the acrylate monomer and a crosslinking agent, and the monomer concentration in the aqueous solution of 20 wt% to 60 wt%, dispersed bubbles of the inert gas The method for producing a water-absorbent resin according to any one of claims 1 to 4, which is obtained by polymerizing the acrylate monomer and the crosslinking agent in a state. The method for producing a water-absorbent resin according to any one of claims 1 to 5, further comprising secondary crosslinking in the vicinity of the surface of the particulate matter obtained by crushing and drying the hydrogel. .

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