JP4676625B2 - Method for producing water absorbent resin powder - Google Patents

Method for producing water absorbent resin powder Download PDF

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JP4676625B2
JP4676625B2 JP2001052664A JP2001052664A JP4676625B2 JP 4676625 B2 JP4676625 B2 JP 4676625B2 JP 2001052664 A JP2001052664 A JP 2001052664A JP 2001052664 A JP2001052664 A JP 2001052664A JP 4676625 B2 JP4676625 B2 JP 4676625B2
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water
absorbent resin
resin powder
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JP2002121291A (en
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邦彦 石▲崎▼
照幸 神頭
信幸 原田
卓己 初田
眞一 藤野
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Nippon Shokubai Co Ltd
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Description

【０００１】
【発明の属する技術分野】
本発明は、吸水性樹脂粉末の製造方法に関するものである。さらに詳しくは、粒度分布や物性に優れた吸水性樹脂粉末の製造方法であって、製造工程での付着や凝集を防止した上、さらにエネルギー効率や乾燥効率、生産性に優れた製造方法を提供するものである。
さらに、得られた粉末に水性液を添加して改質された吸水樹脂粉末を得る方法において、特殊な混合機や有機溶媒を特に使用しなくても、水性液の均一混合性をより改善して、吸水性樹脂粉末の物性をさらに改良する方法に関する。
【０００２】
【従来の技術】
近年、大量の水を吸収させることを目的として、紙オムツや生理用ナプキン、失禁パット等の衛生材料を構成する材料の一つに吸水性樹脂が幅広く利用されている。また衛生材料以外にも、土壌保水剤並びに食品等のドリップシート等、吸水、保水を目的として吸水性樹脂が広範囲に利用されている。
上記の吸水性樹脂としては、例えば、ポリアクリル酸部分中和物架橋体、澱粉−アクリロニトリル共重合体の加水分解物、澱粉−アクリル酸グラフト重合体の中和物、酢酸ビニル−アクリル酸エステル共重合体の鹸化物、アクリロニトリル共重合体もしくはアクリルアミド共重合体の加水分解物またはこれらの架橋体、カルボキシメチルセルロース架橋体、２−アクリルアミド−２−メチルプロパンスルホン酸（ＡＭＰＳ）の共重合架橋体、ポリエチレンオキサイド架橋体、ポリアリルアミン架橋体、ポリエレンイミン架橋体等が知られ、これらの多くは粉末状で使用されている。
【０００３】
これら吸水性樹脂の製造方法としては、必要により架橋剤を含む単量体の水溶液を重合させて得られた含水ゲル状架橋重合体を乾燥してさらに必要により粉砕することで粉末として得る方法が主流であるが、吸水性樹脂の含水ゲル状架橋重合体は、その高い吸水能、粘着性や付着性、低い耐熱性のために、乾燥や乾燥後の粉砕が非常に困難であり、生産性が低く、得られる吸水性樹脂の物性やエネルギー効率が非常に悪いものであった。
かかる吸水性樹脂の含水ゲル状架橋重合体の乾燥方法としては、例えば、ドラムドライヤー乾燥（特開昭５４−５３１６５号）、乾燥した粉末状のアクリル酸重合体と含水ゲルを混合して攪拌乾燥する方法（特開昭５７−１１７５５１号）、共沸脱水（特開昭５７−１９８７１４号）、特定露点での乾燥（特開平１−２６６０４号／米国特許４９２０２０２号）、凍結乾燥（特開平１−３０４１２７号、特開平１−３０４１２８号）、円筒状乾燥機中で攪拌乾燥する方法（特開平２−２４０１１２号／米国特許５００５７７１号）、特定孔でゲルを押し出した後に乾燥する方法（米国特許５２７５７７３号）、マイクロ波乾燥（特開平５−２０９０１０号／米国特許５０７５３４４号）、特定のゲル細断機を用いた後に熱風乾燥する方法（特開平５−２３０１２４号）、差圧を測定しながら熱風乾燥する方法(特開平８−７３５１８号)、界面活性剤を加えて攪拌乾燥する方法（特開平８−１３４１３４号）、静置乾燥した後に粉砕して次いで攪拌ないし流動乾燥する方法（特開平１１−２４０９１４号／欧州特許０９２６１６２号）などが知られている。
【０００４】
また、乾燥のため、パンチングメタルや金網上に含水ゲル状架橋重合体を積層する乾燥方法は知られているが、乾燥後の乾燥重合体は剥離性が悪く、金網や孔への付着や目詰まりのため、特に熱風乾燥などでは通気性低下に伴う乾燥効率の大幅な低下という問題を有していた。そこで、かかる付着や目詰まりの防止のために、ピンを有した特殊なコンベアを用いる乾燥方法（特開平７−２７００７０号／ドイツ特許１９５１１７６９号）も知られている。
さらに吸水性樹脂は物性（吸水倍率、水可溶分、通液性など）以外にも、その粒度分布が重要であり、特定の狭い粒度の吸水性樹脂（特開平１−１３２８０２号／米国特許５０６１２５９号、特開平２−１９６８０２号／米国特許５２４４７３５号、特開平２−１９１６０４号／米国特許４９７３６３２号、特開平６−５０７５６４号／米国特許５４１９９５６号、欧州特許０６２９４１１号）の重要性も知られており、また、粒度分布が複数の吸水性樹脂（欧州特許０８４５２７２号、特開平１１−１３０９７８号）も知られている。
【０００５】
そこで、かかる目的とする粒度調整の為の分級方法として、効率的な分級が求められ、乾燥後の吸水性樹脂の分級方法として、加熱ないし保温させた篩を用いる方法（特開平１０−２０２１８７号／欧州特許０８５５２３２号）、テフロンなどで被覆した分級網を用いる方法（特開平１１−１５６２９９号）も知られている。粉砕前または粉砕工程中に、乾燥時の未乾燥物を分級する方法（特開平１１−２９２９１９号／欧州特許０９４８９９７号）も知られている。
しかしながら、これらの方法にあっても、吸水性樹脂やその含水ゲル状架橋重合体はその高い吸水能や粘着性、低い耐熱性のために、乾燥や乾燥後の粉砕が非常に困難であり、得られる吸水性樹脂の物性や粒度分布の低下が見られ、しかも、エネルギー効率や生産性が非常に悪いものであった。また、粉砕後や分級後にも製造工程で粉末の凝集が見られて、生産効率や品質を低下させるという問題を有していた。
【０００６】
さらに、得られた重合体粉末に対して、水単独または添加剤を含む水性液を添加することで吸水性樹脂粉末の粒度分布や加圧下吸収特性を改良する方法は知られ、かかる方法は、造粒（米国特許５３６９１４８号）や表面架橋（米国特許５４０９７７１号，同５４２２４０５号，同５５９７８７３号）、残存エポキシ化合物の低減（米国特許５９８１０７０号）などとして多用されている。
しかし、吸水性樹脂は瞬時に水を吸収し粘着性を発揮するため、従来、水性液の不均一な混合のために、その物性改良も不十分であるのみならず、さらに場合よっては、不均一な混合によって生成した吸水性樹脂の凝集物が混合機中に付着して、連続操業そのものが困難であった。また、架橋剤やその溶媒として多価アルコールは物性面や安全性面でも好ましいが、その高い親水性や粘度のために、これら水性液の中でも多価アルコール水溶液の吸水性樹脂への均一な混合は特に困難であった。
【０００７】
そこで、吸水性樹脂粉末に水性液を添加して改質する際に、特殊な混合機の使用（欧州特許０４５０９２３号，欧州特許０８１２８７３号など）、無機粉末の使用（米国特許４５８７３０８号）、水性液中に有機溶媒を併用する技術（米国特許４７３４４７８号）は知られているが、有機溶媒の使用、特に揮発性有機溶媒の使用はコストや環境問題・安全性に加えて、物性低下を引起こす問題を伴っていた。さらに、吸水性樹脂に水性液を添加する際に、樹脂の物性（AUL/Absorbency under Load）を特定範囲に制御する技術（ＷＯ９８／４９２２１号）も知られているが、かかる方法では、適用される吸水性樹脂粉末も非常に限られ且つその製造も困難であった。
【０００８】
【発明が解決しようとする課題】
本発明は、上記従来の問題点に鑑みなされたものであり、その目的は、上記現状のため、含水ゲル状架橋重合体を熱劣化なく、効率的に乾燥ないし粉砕し粒度調整することで、粒度分布が狭く且つ高物性の吸水性樹脂粉末を製造することができるとともに、その製造工程での付着や凝集を防止した上、さらにエネルギー効率よく且つ高生産性を示す製造方法を提供することである。
さらに、水性液を添加する方法において、混合性をさらに改良して、特殊な混合機や有機溶媒を使用せずとも、均一な水性液（特に架橋剤水溶液や多価アルコール水溶液）の添加によって吸水性樹脂粉末の物性をより改良することである。
【０００９】
【課題を解決するための手段】
本願発明者等は、上記目的を達成すべく鋭意検討した結果、架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕する吸水性樹脂粉末の製造方法であって、当該粉砕後の吸水性樹脂粉末の重量平均粒子径が２００〜６００μｍの範囲であり、さらに１５０μｍ以下ないし８５０μｍ以上の粒子の合計割合が１５重量％以下であり、加熱乾燥後の乾燥重合体を粉砕前または粉砕時に強制冷却することを特徴とする製造方法によって、エネルギー効率もよく、製造工程の粉末の凝集もなく、乾燥時の熱劣化や付着も非常に少なく、乾燥後の粉砕も極めて効率的になされることを見出し本発明を完成した。
【００１０】
さらに、吸水性樹脂粉末を強制冷却しさらに嵩比重を調整することで、従来困難であった水性液（特に架橋剤水溶液や多価アルコール水溶液）の混合性を改良し、連続操業性や物性を改良できることを見出し本発明を完成した。
すなわち、本発明に係る吸水性樹脂粉末の製造方法は、
架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕する吸水性樹脂粉末の製造方法であって、
当該粉砕後の吸水性樹脂粉末の重量平均粒子径が２００〜６００μｍの範囲であり、さらに１５０μｍ以下ないし８５０μｍ以上の粒子の合計割合が１５重量％以下であり、
加熱乾燥後の乾燥重合体を粉砕前または粉砕時に強制冷却する、
ことを特徴とする。
【００１１】
また、本発明に係る別の吸水性樹脂粉末の製造方法は、
架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕する吸水性樹脂粉末の製造方法であって、
加熱乾燥後の乾燥重合体を強制冷却して得られた熱を吸水性樹脂の製造工程における強制加熱に再利用する、
ことを特徴とする。
また、本発明に係る別の吸水性樹脂粉末の製造方法は、
架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕して得られた粉末に混合機中で水性液を添加する吸水性樹脂粉末の製造方法であって、
加熱乾燥温度が１１０〜２３０℃の範囲であること、水性液添加前に乾燥重合体を８０〜３５℃に強制冷却すること、および、粉砕後の乾燥重合体の嵩比重（ＪＩＳ Ｋ ３３６２に準じて測定）を０．６５ｇ／ｍｌ以上とする、
ことを特徴とする。
【００１２】
また、本発明に係る別の吸水性樹脂粉末の製造方法は、
架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕して得られた粉末に混合機中で水性液を添加する吸水性樹脂粉末の製造方法であって、
加熱乾燥温度が１１０〜２３０℃の範囲であること、水性液添加前に乾燥重合体を８０〜３５℃に強制冷却すること、および、混合機の内壁温度が４０℃以上の攪拌混合機であること、および、１１０〜２３０℃に再加熱すること、
を特徴とする。
【００１３】
また、本発明に係る別の吸水性樹脂粉末の製造方法は、
架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕する吸水性樹脂粉末の製造方法であって、
加熱乾燥後の乾燥重合体を強制冷却すること、
乾燥重合体を粉砕して嵩比重（ＪＩＳ Ｋ ３３６２に準じて測定）０．６５ｇ／ｍｌ以上の吸水性樹脂粉末とすること、
冷却された吸水性樹脂粉末をさらに表面架橋すること、
を特徴とする。
【００１４】
また、本発明に係る別の吸水性樹脂粉末の製造方法は、
架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕する吸水性樹脂粉末の製造方法であって、
加熱乾燥後の乾燥重合体を強制冷却すること、
乾燥重合体を粉砕して嵩比重（ＪＩＳ Ｋ ３３６２に準じて測定）０．６５ｇ／ｍｌ以上の吸水性樹脂粉末とすること、
冷却された吸水性樹脂粉末にさらに水性液を添加すること、
水性液が内壁が加熱された攪拌混合機で添加されること、
を特徴とする。
【００１６】
【発明の実施の形態】
以下に本発明の実施の一形態について詳しく説明する。
本発明の吸水性樹脂粉末の製造方法では、架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕する吸水性樹脂粉末の製造方法であって、当該粉砕後の吸水性樹脂粉末の重量平均粒子径が２００〜６００μｍの範囲であり、さらに１５０μｍ以下ないし８５０μｍ以上の粒子の合計割合が１５重量％以下であり、加熱乾燥後の乾燥重合体を粉砕前または粉砕時に強制冷却することを特徴とする製造方法である。
【００１７】
先ず、以下、本発明の含水ゲル状架橋重合体の製造方法について説明する。
本発明における吸水性樹脂とは、飽和膨潤時に無荷重下では自重の３〜１０００倍、好ましくは５〜１０００倍、より好ましくは１０〜８００倍、さらに好ましくは１００〜７００倍のイオン交換水を吸収して水不溶性の膨潤含水ゲルを形成しうる架橋重合体のことである。なお、本発明での水不溶性とは通常、吸水性樹脂中の水可溶成分量が４０重量％以下、好ましくは２０重量％以下、さらに好ましくは１５重量％以下、特に好ましくは１０重量％以下、最も好ましくは５重量％以下である。なお、これらの物性の測定法は、後述の実施例の欄で説明する。水可溶成分量が多いと、諸物性（加圧下吸収，加圧下通液量など）の低下のみならず、吸水性樹脂粉末の水性液の均一な添加が困難となるので好ましくない。
【００１８】
本発明にかかる吸水性樹脂粉末の製造方法において用いられる含水ゲル状架橋重合体は、架橋剤を含む単量体水溶液を重合してなる重合体である。上記含水ゲル状架橋重合体としては、吸水性のカチオン性、アニオン性、ノニオン性の架橋重合体の１種または混合物が挙げられるが、本発明の効果を最も発揮する点から、好ましくは、必須にアニオン性架橋重合体を主成分とし、さらには好ましくは、官能基の主成分はカルボキシル基であることが好ましい。
本発明では、その効果の大きさから、アニオン性架橋重合体は酸基含有不飽和単量体（塩）としてアクリル酸（塩）を用いた含水ゲル状架橋重合体が好ましく、また、０〜９０モル％、さらには０〜８０モル％が中和されたアクリル酸（塩）を重合してなる含水ゲル状架橋重合体であることが更に好ましく、特に、０〜１０モル％が中和されたアクリル酸（塩）を重合してなる含水ゲル状架橋重合体であることが更により好ましい。すなわち、従来、ポリアクリル酸架橋体、特に未中和ないし低中和のポリアクリル酸架橋体では乾燥工程や粉砕工程での物性低下が大きかったため、本発明の方法が好適に適用される。
【００１９】
また、上記単量体は、上記アクリル酸（塩）を主成分とし、必要に応じて、上記アクリル酸（塩）以外のその他の単量体、つまり、上記アクリル酸（塩）と共重合可能なその他の単量体を含んでいてもよいし、また、アクリル酸以外の単量体で吸水性樹脂を得てもよい。
用いられるアクリル酸以外の単量体としては、特に限定されるものではないが、具体的には、例えば、メタクリル酸、マレイン酸、クロトン酸、ソルビン酸、イタコン酸、ケイ皮酸、無水マレイン酸、ビニルスルホン酸、アリルスルホン酸、ビニルトルエンスルホン酸、スチレンスルホン酸、２−（メタ）アクリルアミド−２−メチルプロパンスルホン酸、２−（メタ）アクリロイルエタンスルホン酸、２−（メタ）アクリロイルプロパンスルホン酸、２−ヒドロキシエチル（メタ）アクリロイルホスフェート等の酸基含有不飽和単量体およびその塩；アクリルアミド、メタアクリルアミド、Ｎ−エチル（メタ）アクリルアミド、Ｎ，Ｎ−ジメチル（メタ）アクリルアミド、２−ヒドロキシエチル（メタ）アクリレート、２−ヒドロキシプロピル（メタ）アクリレート、メトキシポリエチレングリコール（メタ）アクリレート、ポリエチレングリコールモノ（メタ）アクリレート、ビニルピリジン、Ｎ−ビニルピロリドン、Ｎ−アクリロイルピペリジン、Ｎ−アクリロイルピロリジン等のノニオン性の親水基含有不飽和単量体等が挙げられる。これらその他の単量体は、一種類のみを用いてもよく、適宜、二種類以上を混合して用いてもよい。これらその他の不飽和単量体を用いる場合には、アクリル酸を含む単量体中のその他の不飽和単量体割合が５０モル％以下、好ましくは３０モル％以下となるように設定すればよい。
【００２０】
本発明で酸基含有単量体や塩基含有単量体を用いる場合、単量体ないし重合体の酸基官能基ないし塩基官能基は中和してもよい。本発明で用いられる中和剤としては、特に限定されるものではなく、公知の無機または有機の塩基または酸を単量体ないし重合体に対して使用することができる。
例えば、本発明で酸基含有単量体を用いる場合、単量体ないし重合体の中和剤の塩基としては、具体的には、例えば、水酸化ナトリウム、水酸化カリウム、水酸化リチウム、炭酸リチウム、水酸化アンモニウム、炭酸ナトリウム、炭酸カリウム、炭酸アンモニウム、炭酸水素ナトリウム、炭酸水素カリウム、炭酸水素アンモニウムなどの無機塩基、エタノールアミン、ジエタノールアミン、トリエタノールアミン、ポリエチレンイミン、ポリアリルアミン、（ポリ）リジン、（ポリ）アルギニンなどの有機塩基が挙げられる。また、本発明で塩基含有単量体を用いる場合、同様に中和剤として無機酸ないし有機酸が適宜選択される。
【００２１】
なお、高分子の中和剤（例えば、ポリアミン）を用いる場合は架橋体としてもよいが、これら中和剤の中でもアルカリ金属塩、特にリチウム塩ないしナトリウム塩が好ましく用いられ、吸水性樹脂の酸基の５０〜９０モル％、さらには６０〜８０モル％が中和される。本発明で得られる吸水性樹脂の最終的な中和率は上記範囲が好ましい。
また、中和は上記塩基や酸を水溶液、分散液またはゲルとして行ってもよいし、塩基や酸を固体のまま加えるいわゆるドライブレンド（粉体混合）で行ってもよい。また、中和は単量体でもよく、乾燥前の含水ゲル状架橋重合体で行ってもよいし、乾燥後の乾燥重合体やその粉砕物や分級物に対して行ってもよいし、これら中和を併用してもよい。さらに、中和は酸基と塩基を完全に反応させてもよいし、ドライブレンドなどの方法で一部のみを反応させて、上記酸基と上記塩基との混合物である吸水性樹脂組成物を得る事で中和としてもよい。
【００２２】
また、本発明で中和する場合、その手法として、含水ゲル状架橋重合体またはその乾燥重合体の後中和、特に乾燥重合体の後中和は本発明の好適な手法の一つである。すなわち、本発明では、未中和ないし低中和のポリアクリル酸架橋体をその物性低下なく効率的に乾燥（粉末化）できるので、ポリアクリル酸架橋体粉末を用いた後中和が可能であり、よって、ポリアクリル酸架橋体粉末を後中和するという方法で、さらに高物性の吸水性樹脂を得る事もできて好ましい。
また、上記含水ゲル状架橋重合体を得る際には、その手段は、重合体が水不溶性となればラジカル架橋や自己架橋などでもよいが、通常、内部架橋剤を用いて架橋構造を重合体の内部に導入する。上記の内部架橋剤は、重合性不飽和基および／または反応性基を一分子中に複数有する化合物であればよく、単量体と共重合および／または反応する置換基を一分子中に複数有する化合物であればよい。また、反応する置換基を一分子中に複数有する化合物を用いる場合、重合後の水溶性ないし水不溶性の重合体ゲルに架橋剤を均一に添加してその内部を後架橋してもよい。
【００２３】
上記内部架橋剤としては、具体的には、例えば、Ｎ，Ｎ’−メチレンビス（メタ）アクリルアミド、（ポリ）エチレングリコールジ（メタ）アクリレート、（ポリ）プロピレングリコールジ（メタ）アクリレート、トリメチロールプロパントリ（メタ）アクリレート、トリメチロールプロパンジ（メタ）アクリレート、グリセリントリ（メタ）アクリレート、グリセリンアクリレートメタクリレート、エチレンオキサイド変性トリメチロールプロパントリ（メタ）アクリレート、ペンタエリスリトールテトラ（メタ）アクリレート、ジペンタエリスリトールヘキサ（メタ）アクリレート、トリアリルシアヌレート、トリアリルイソシアヌレート、トリアリルホスフェート、トリアリルアミン、ポリ（メタ）アリロキシアルカン、（ポリ）エチレングリコールジグリシジルエーテル、グリセロールジグリシジルエーテル、エチレングリコール、ポリエチレングリコール、プロピレングリコール、グリセリン、ペンタエリスリトール、エチレンジアミン、ポリエチレンイミン、グリシジル（メタ）アクリレート等が挙げられるが、特に限定されるものではない。
【００２４】
これら内部架橋剤は、一種類または二種類以上を混合ないし分割して用いてもよい。上記例示の内部架橋剤のうち、重合性不飽和基を一分子中に複数有する内部架橋剤を重合時に用いることにより、得られる吸水性樹脂の物性をより一層向上させることができるので好ましい。
上記内部架橋剤の使用量は、架橋剤の種類や目的の架橋密度にもよるが、前記単量体に対して、好ましくは０．００５〜３モル％、より好ましくは０．０１〜１．５モル％、さらに好ましくは０．０５〜１モル％の範囲で用いられる。上記内部架橋剤の使用量が０．００５モル％よりも少ない場合、並びに、３モル％よりも多い場合には、所望の物性を備えた吸水性樹脂が得られない虞れがある。
【００２５】
尚、上記重合に際しては、反応系に、澱粉、澱粉の誘導体、セルロース、セルロースの誘導体、ポリビニルアルコール、ポリアクリル酸（塩）、ポリアクリル酸（塩）架橋体等の親水性高分子（以上のものについての添加量は、単量体１００重量部に対して０〜４０重量部が好ましく、０〜１０重量部がより好ましい）；次亜リン酸（塩）等の連鎖移動剤、キレート剤、炭酸塩などの発泡剤等（以上のものについての添加量は、単量体１００重量部に対して０〜５重量部が好ましく、０〜１重量部がより好ましい）を添加してもよい。
上記単量体の重合方法としては、特に限定されるものではなく、例えば、水溶液重合、逆相懸濁重合、バルク重合、沈澱重合等の公知の方法を採用することができる。このうち、重合反応の制御の容易さ、および、得られる吸水性樹脂の性能面から、本発明では、単量体成分を水溶液にして重合させる方法、即ち、水溶液重合および逆相懸濁重合が好ましい。
【００２６】
なお、逆相懸濁重合とは、単量体水溶液を疎水性有機溶媒に懸濁させる重合法であり、例えば、米国特許４０９３７７６号、同４３６７３２３号、同４４４６２６１号、同４６８３２７４号、同５２４４７３５号などの米国特許に記載されている。水溶液重合は分散溶媒を用いずに単量体水溶液を重合する方法であり、例えば、米国特許４６２５００１号、同４８７３２９９号、同４２８６０８２号、同４９７３６３２号、同４９８５５１８号、同５１２４４１６号、同５２５０６４０号、同５２６４４９５号、同５１４５９０６号、同５３８０８０８号などの米国特許や、欧州特許０８１１６３６号、同０９５５０８６号，同０９２２７１７号などの欧州特許に記載されている。本発明ではこれらを含め特に重合法に限定されないが、乾燥や粉砕が従来困難であった水溶液重合に特に好適に本発明は使用される。
【００２７】
上記重合方法として水溶液重合および逆相懸濁重合を採用する場合の単量体成分の濃度、即ち、水溶液中における単量体の割合は、特に限定されるものではないが、物性面から好ましくは１０〜７０重量％、より好ましくは１５〜６０重量％、さらに好ましくは２０〜５０重量％、特に好ましくは３０〜４５重量％の範囲内である。
また、反応温度や反応時間等の反応条件は、用いる単量体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が、通常、０℃〜沸点以下、好ましくは１０〜１１０℃、より好ましくは１５〜１００℃の範囲内（最低〜最高温度、または、開始温度〜ピーク温度）での重合が行われ、かかる重合は窒素などの不活性ガスの雰囲気下で行われることが好ましい。さらに、重合時の雰囲気も減圧や加圧にしてもよいが、通常は常圧で行われる。
【００２８】
重合開始には、例えば、過硫酸カリウム、過硫酸アンモニウム、過硫酸ナトリウム、ｔ−ブチルハイドロパーオキサイド、過酸化水素、２，２’−アゾビス（２−アミジノプロパン）二塩酸塩等のラジカル重合開始剤、或いは、紫外線重合開始剤を必要により用いての紫外線や電子線等の活性エネルギー線等を用いることができ、これらを併用してもよい。
また、かかる酸化性ラジカル重合開始剤を用いる場合には、例えば、亜硫酸ナトリウム、亜硫酸水素ナトリウム、硫酸第一鉄、Ｌ−アスコルビン酸等の還元剤を併用してレドックス重合を行ってもよい。これら重合開始剤の使用量は０．００１〜２モル％の範囲内が好ましく、０．０１〜０．５モル％の範囲内がより好ましい。尚、重合開始剤は、通常、水等の溶媒に溶解または分散させて添加すればよい。
【００２９】
上記重合によって得られた含水ゲル架橋架橋重合体は必要により細分化され、次いで乾燥される。本発明で好ましくは、物性面からも乾燥は粒子状の含水ゲル状架橋重合体（例えば、平均粒子径が２ｃｍ以下、好ましくは１ｃｍ以下、より好ましくは５ｍｍ以下）として行われる。本発明で含水ゲル状架橋重合体を粒子状とする為の細分化方法としては、ニーダーなどを用いて重合と同時に細分化を行ってもよいし、また、重合後に別途細分化してもよいし、重合時の細分化と重合後の細分化を併用してもよい。なお、含水ゲル状重合体が粒子状で乾燥されない場合、例えば、フィルム状などでは、物性や粒度が劣る場合ある。
【００３０】
乾燥に先立っての含水ゲル状架橋重合体の粒子径としては、乾燥効率や物性面からも重量平均粒径で、好ましくは４５〜４０００μｍ、より好ましくは５０〜２０００μｍ、より好ましくは１００〜１５００μｍ、更に好ましくは２００〜１０００μｍの範囲である。この様な細分化に適した装置としては、例えば、ニーダー、カッター刃を備えた縦切り型スリッター、カッター刃を備えた横切り型スリッター、回転刃を備えたカッター型の粉砕機、所定の孔径のミートチョパーなどが例示できる。なお、含水ゲル状架橋重合体の重量平均粒径が上記範囲を外れると、得られる吸水性樹脂粉末の吸水倍率の低下や水可溶分の増加などを引き起こす恐れがある。
【００３１】
こうして得られた含水ゲル状架橋重合体は必須に加熱乾燥される。なお、本発明で乾燥とは、上記含水ゲル状架橋重合体をその固形分が８０重量％以上、好ましくは８５重量％以上、より好ましくは９０％重量以上、特に好ましくは９３重量％以上の固体状態にすることを示す。
また、本発明におけるかかる乾燥は、必ずしも固形分１００重量％（水分ゼロ）の乾燥重合体にする必要はなく、好ましくは固形分９９重量％以下、さらに好ましくは固形分９８重量％以下、さらにより好ましくは９７重量％以下、最も好ましくは９７〜９３重量％の範囲にまで含水ゲル状架橋重合体が乾燥される。
【００３２】
すなわち、乾燥後の固形分が高いと、表面架橋による物性も向上しやすく、また、その後の製造工程での粉末の凝集が少なく粉体での扱いが容易であるが、乾燥に時間を要するのみならず、粉砕時やその後の工程や使用時の微粉の増加や長時間の乾燥で物性低下を引起こす場合がある。しかし、乾燥後に強制冷却する本発明では、製造工程の粉末の凝集防止のため、また、乾燥重合体の粉砕のため、従来の様に、過度に乾燥重合体や吸水性樹脂粉末の固形分を上昇させる必要もないため、乾燥時間の短縮や物性の向上が図れるので好ましい。
本発明で用いられる加熱乾燥方法としては、特に限定されるものではなく、例えば、熱風乾燥、ドラムドライヤー等を用いた薄膜乾燥、減圧乾燥法、攪拌乾燥、流動床乾燥など乾燥方法の１種または２種以上を用いることができるし、乾燥の連続または回分は特に問わない。これらの中でも物性面からも乾燥効率の面からも、本発明では、熱風乾燥、特に連続の熱風乾燥が好ましく用いられ、例えば、ベルト上で静置乾燥すればよい。
【００３３】
かかる熱風乾燥には、乾燥効率から、金網／ないし孔やスリットを有するパンチングメタル上に粒子状の含水ゲル状架橋重合体を積層した上、ゲルの上下方向ないし横方向、好ましくは上下方向に、積層した粒子の空隙間に熱風を通気すればよい。用いられる金網や孔径として、例えば、孔や金網の場合、０．１〜５ｍｍ、さらには０．２〜２ｍｍ程度の通気孔を有すればよい。また、金網ないしパンチングメタル上でのゲルの積層は、乾燥後の物性面から１〜２０ｃｍ、好ましくは１．５〜１０ｃｍ、より好ましくは２〜８ｃｍの一定厚みに粒子状の含水ゲル状架橋重合体を積層すればよい。
【００３４】
上記の含水ゲル状架橋重合体を乾燥させる際の乾燥温度は、物性面や生産性の面からも通常１００℃以上、さらには１１０〜２３０℃、好ましくは１３０〜２００℃、特に好ましくは１５０〜１９０℃の程度に設定すればよい。なお、乾燥温度は材料温度または熱媒（熱風など）の温度で規定されるが、好ましくは熱媒温度で規定される。また、乾燥期間中で乾燥温度は一定であってもよく、上記温度範囲で乾燥途中で適宜変化させてもよい。さらに、熱風乾燥する際、熱風の露点は、物性やエネルギー効率から、好ましくは４０〜１００℃、より好ましくは５０〜９０℃、さらに好ましくは６０〜８５℃の範囲である。
【００３５】
こうして得られた乾燥重合体は必須に強制冷却された後、次いで、または同時に粉砕される。本発明において強制冷却と粉砕は同時に行ってもよいが、好ましくは、強制冷却後に粉砕される。本発明でいう強制冷却とは外的且つ意図的な乾燥重合体の冷却操作ないし冷却工程であり、また、粉砕とは得られた乾燥重合体ないしその凝集物（ブロック状物）を流動性ある粉末にする機械的操作であり、さらに、解砕とは乾燥重合体の物理的破壊や粒径の減少にまでは至らず、数ｍｍ〜数１０程度ｍｍにまで軽く凝集を解す機械的操作である。
なお、積層されて乾燥された粒子状含水ゲル状架橋重合体は、乾燥後、粒子間の凝集で流動性を失ったブロック状乾燥物となり易いことも併記しておく。かかるブロック状物は乾燥重合体粒子の凝集体であるため、連続した空隙と、ブロック内部への通気性は有しているが、凝集の為に流動性がないため、粉砕（解砕）工程を必要とする。
【００３６】
本発明で強制冷却する方法としては、乾燥工程と粉砕工程の間に意図的に冷却工程を設けることで所定温度まで乾燥重合体を冷却すればよく、例えば、加熱乾燥して得られた乾燥重合体を、▲１▼冷却伝熱面を有し必要により攪拌される容器（ホッパー）や筒中に投入して強制冷却する方法、▲２▼（乾燥に用いた）連続ベルト上で十分に放冷する方法、▲３▼冷風を重合体に通気して強制冷却する方法、▲４▼冷えた空気を用いて輸送と同時に強制冷却する方法、▲５▼冷却伝熱面を有する低温スクリューコンベアーなどが挙げられる。
これら方法の中で、冷却効率や乾燥重合体の流動性から、本発明では好ましくは、▲３▼冷風を通気する方法が用いられ、その場合、乾燥重合体の表面のみを通気してもよいが、好ましくは、積層した乾燥重合体ないしそのブロック状物を上下方向ないし横方向、好ましくは上下方向に、積層した粒子の空隙間を通気する事でより効率的な強制冷却が行えるので好ましい。なお、積層する場合、その厚みは前述の範囲が好ましい。
【００３７】
本発明で強制冷却は粉砕前または粉砕時が必須であり、また、実験室での小スケールの重合・乾燥・粉砕であり／さらに各々の実験操作間が非連続で且つ間隔が数１０分〜数時間以上空くため、自然に放冷されやすい実験室スケールの乾燥および粉砕と違って、むしろ、生産スケールの乾燥では粉砕前又は粉砕時の強制冷却を行わない場合、本発明の目的が達成されないことが分かった。すなわち、本発明は、生産設備での大スケール（例えば、１ラインあたり、吸水性樹脂粉末が１ｔ／日以上、好ましくは１０ｔ／日以上）の連続乾燥、連続粉砕およびその後の連続水性液添加に、より好適である。
【００３８】
本発明の特徴である加熱乾燥後の強制冷却を行わない場合、粉砕ないし分級効率が大きく低下して、粒度分布に優れた吸水性樹脂粉末を生産性よく得ることができない。さらに、金網ないしパンチングメタル上で熱風乾燥する場合、従来、乾燥重合体が金網やパンチングメタルに付着したり目詰まりを起こし通気性や乾燥効率や生産性を大きく低下させていたが、強制冷却する本発明ではかかる問題もなく、特別な付着防止装置（特開平７−２７００７０号）や／乾燥機の附着や目詰まりの定期的な除去も必要ない。しかも、粉砕前または粉砕時に、強制冷却することで、得られる吸水性樹脂粉末の粒度分布や粉砕速度も優れて、さらに、粉砕機での附着や製造工程での粉末の凝集も大きく低減される。また、その後の製造工程での粉末の凝集防止のため、過度に吸水性樹脂粉末を乾燥する必要もなく、よって、乾燥時間の短縮や物性の向上も達成される。
【００３９】
本発明で▲３▼の方法で用いられる冷風（気体）は、目的の乾燥重合体の温度によって適宜決まるが、冷却効率から６０℃以下、好ましくは５０〜−５０℃、さらに好ましくは４０〜−１０℃、特に好ましくは３５〜５℃の気体での強制冷却がなされ、その際、気体の露点は好ましくは６０℃以下、さらに好ましくは５０℃以下である。また、かかる気体は窒素などの不活性ガス、不活性ガスと空気の混合気体でもよいが、好ましくは空気、特に、フィルターを通した空気が用いられる。
さらに、その風速は１０〜０．１ｍ／秒、さらには５〜０．５ｍ／秒程度の冷風であり、冷却時間は好ましくは６０〜０．１分、より好ましくは２０〜０．２分、さらに好ましくは１０〜０．５分の範囲である。
【００４０】
本発明における強制冷却温度としては、本発明を達成する上で乾燥重合体の温度が９５℃以下、好ましくは８５〜３５℃、より好ましくは８０〜４０℃、さらに好ましくは７０〜４５℃の範囲に強制冷却される。なお、強制冷却温度は、接触式温度計や非接触式温度計（赤外線温度計など）などで適宜、材料温度を測定することで求められ、また、必要により、制御される。
乾燥重合体の温度が９５℃を超えると、乾燥機の金網やパンチングメタルからの剥離性が困難で乾燥効率が低く、また、乾燥重合体の粉砕や分級の効率が大きく低下して、結果的に粒度分布の狭い優れた吸水性樹脂粉末を得る事が困難である。また、冷却温度が低く過ぎると、冷却に大きな時間や設備が必要であるのみならず、意外なことに、粉砕時や分級時に吸水性樹脂粉末の凝集物が生成するので好ましくない。さらに、過度の冷却は、後述の強制加熱や表面架橋にも、物性やエネルギー面で不利なこともある。
【００４１】
また、本発明を達成する上で、その強制冷却による乾燥重合体の温度低下は、加熱乾燥温度にもよるが、強制冷却前の乾燥重合体と比較して、冷却前後の重合体の温度変化が好ましくは４０℃以上、より好ましくは６０℃以上、さらに好ましくは８０℃以上、特に好ましくは１００℃以上の冷却が乾燥重合体に対してなされることで、上記目的とする乾燥重合体の温度（例えば、より好ましくは８０〜４０℃）にまで強制冷却すればよい。
なお、強制冷却によって乾燥重合体より奪われた熱は、好ましくはリサイクルされる。例えば、前述のように本発明で加熱乾燥は熱風乾燥（特に好ましくは、１５０〜１８０℃）であり、また、強制冷却は風冷（特に好ましくは７０〜４５℃の範囲に重合体を強制冷却）されるが、本発明でかかる熱風乾燥と風冷による強制冷却を行う場合、乾燥重合体の強制冷却に用いられた冷風は、その風量や通気量、重合体の温度などにより適宜制御されるが、温風ないし熱風（通常、５０℃以上であり、５０〜２００℃が好ましく、より好ましくは６０〜１５０℃、さらに好ましくは７０〜１１０℃）となるため、リサイクルされて、温風ないし熱風としてそのまま吸水性樹脂の製造工程に利用されたり、再加熱されて前述の熱風乾燥などの吸水性樹脂の製造工程に利用すればよい。
【００４２】
本発明で強制冷却によって得られた熱は、好ましくは再利用される。再利用される製造工程としては、保温工程などもあるが、前述の乾燥工程が最も好ましい。すなわち、本発明で強制冷却に用いられる冷風は、乾燥重合体を通気後に温風となるため、本発明では好ましくは、強制冷却後の温風（例えば、６０〜１５０℃）を配管を通じて熱風乾燥機の空気供給口に供給して、乾燥に用いる熱風の原料として、連続乾燥を行うことが可能である。このようにして、本発明の熱風乾燥では、室温の空気を用いる代わりに強制冷却で発生した温風を用いて、熱風を製造しているため、その分、大きな省エネルギーを実現でき、かつ、温風（廃ガス）を環境に排出しない利点を有する。かかるリサイクルの観点からも、本発明の強制冷却には冷風を重合体に通気する強制冷却、また、本発明の加熱乾燥には熱風乾燥が用いられる。
【００４３】
すなわち、本発明は、架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕する吸水性樹脂粉末の製造方法であって、加熱乾燥後の乾燥重合体を強制冷却して得られた熱を吸水性樹脂の製造工程における強制加熱に再利用することを特徴とする、吸水性樹脂粉末の製造方法をも提供する。ここにおいて、強制加熱に再利用するとは、強制冷却工程で得られた熱を、強制加熱工程で利用することであり、該強制冷却工程と該強制加熱工程は、同一の生産ラインの中に含まれるものでもよく、また、それぞれが別々の生産ラインに含まれる工程であってもよい。
【００４４】
また、本発明で熱風乾燥と風冷を行う場合、乾燥装置および冷却装置としては、流動床などを別途設置してもよいし、例えば、連続熱風乾燥を行う場合、ベルト式乾燥機を用いて乾燥機の後半の一部分を冷却工程に用いることも好ましい方法である。かかる場合、冷却装置を別途設けなくとも、熱風乾燥機のベルト後半の１／４〜１／２０の部分、好ましくは後半１／８〜１／１６の部分を別途区切って冷却装置として冷風を送ることで強制冷却工程とし、さらには乾燥重合体より奪った熱をリサイクルすればよい。
本発明では、乾燥重合体の強制冷却によって得られた熱が再利用されるので、エネルギー効率に優れたプロセスとすることができる。また、乾燥機の後半を強制冷却する事で、ベルトの金網やパンチングメタルからの乾燥重合体の剥離性が飛躍的に改善され、ベルトの目詰まりもなく通気性向上による乾燥効率も向上するので好ましい。
【００４５】
こうして所定温度に強制冷却された乾燥重合体は次いで粉砕ないし分級、好ましくは、必須に粉砕され更に分級される。前記乾燥と粉砕ないし分級は連続工程でなされることが好ましく、乾燥機出口から粉砕機入口までの時間は１０分以内、好ましくは５分以内、さらに好ましくは２分以内でなされる。本発明ではこのような連続工程でも、乾燥工程と粉砕工程の間に強制冷却工程を入れることで、乾燥効率と粉砕効率を飛躍的に向上することが可能である。
本発明で粉砕方法としては、乾燥重合体やその凝集物（ブロック状物）を流動性ある粉末、好ましくは重量平均粒子径２ｍｍ以下の粉末にできれば特に限定されるものではなく、例えば、ハンマー式粉砕機、ロール式粉砕機、またはジェット気流式粉砕機等を用いて粉砕する方法、従来公知の種々の粉砕ないし解砕方法の１種または２種以上を用いることができる。また、乾燥時の凝集が弱い場合、特に粉砕機を用いなくても、乾燥重合体に振動を与えて分級することで重合体の凝集をほぐして粉砕工程としてもよい。
【００４６】
本発明では上記の粉砕後、さらに必要により／好ましくは分級され、粗大粒子や微粉末が除去される。こうして得られる吸水性樹脂粉末の重量平均粒子径は目的に応じて決定されるが、例えば、衛生材料を目的とする場合、最終的に得られる吸水性樹脂粉末は、重量平均粒子径２００〜６００μｍ、さらには３００〜６００μｍ、さらには３００〜５５０μｍの範囲であり、好ましくは、さらに１５０μｍ以下ないし８５０μｍ以上の粒子の合計が１５重量％以下、より好ましくは１０重量％以下、さらに好ましくは５重量％以下である。
特に、本発明においては、粉砕後に得られて次工程に用いられる吸水性樹脂粉末の重量平均粒子径が上記範囲内、すなわち２００〜６００μｍの範囲内であり、さらに１５０μｍ以下ないし８５０μｍ以上の粒子の合計割合が１５重量％以下であることが好ましい。
【００４７】
こうして得られた吸水性樹脂粉末の嵩比重は、モノマー組成に一義的によって決まる真比重（ｇ／ｃｍ３）によって種々変化するが、例えば、吸水性樹脂がポリアクリル酸ナトリウム、特に中和率５０〜９０モル％、さらには６０〜８０モル％の場合、その嵩比重が通常０．６３ｇ／ｍｌ以上、特に０．６５ｇ／ｍｌ以上（ＪＩＳ Ｋ−３３６２の装置で測定）とすることが好ましい。本発明の強制冷却する方法では、粉砕後の吸水性樹脂粉末は鱗片も少なく、より丸みを帯びて均一な形状となるので、嵩比重は高くなり易く、嵩比重は好ましくは０．６５〜０．８９ｇ／ｍｌ、より好ましくは０．６７〜０．８８ｇ／ｍｌ、さらに好ましくは０．７３〜０．８７ｇ／ｍｌ、さらに好ましくは０．７４〜０．８６ｇ／ｍｌ、さらに好ましくは０．７５〜０．８５ｇ／ｍｌに調整される。
【００４８】
粉砕後の嵩比重が０．６３ｇ／ｍｌよりも低いと、温度を制御しても、後述の水性液の混合が困難となり、物性低下（加圧下吸収倍率，加圧下通液性）のみならず、吸水性樹脂粉末の耐衝撃性の（プロセスダメージ）低下、単位体積あたりの重量減による輸送コストアップ、などが見られる場合もあり好ましくない。また、嵩比重が０．８９ｇ／ｍｌよりも高いと、加圧下通液性膨潤時にゲル間の通液空間を確保することが困難になる場合が起こりうる。
上記粉砕後に粗大粒子（例えば、８５０μｍオン品）や微粉（例えば、１５０μｍパス品）は場合により適宜リサイクルすればよい。粗い粒子は再粉砕され、細かい粒子は除去ないし回収されることで、前記粒度分布とすればよい。しかし、本発明では粒度分布がシャープなため、かかるリサイクルの必要性が大きく低減する。なお、吸水性樹脂の微粉のリサイクル方法は、米国特許４９５０６９２号、同５０６４５８２号、同５２６４４９５号、同５４７８８７９号や、欧州特許０８１２８７３号、同０８８５９１７号、同０８４４２７０号などに開示されており、これらの微粉リサイクル方法の本発明への適用も可能である。また、微粉のリサイクル量は全体の１５重量％以下、好ましくは１〜１０重量％、より好ましくは２〜８重量％の範囲である。本発明では粉砕で粒度分布のシャープな吸水性樹脂粉末が高い生産性で得られるため、少量の微粉のリサイクルでさらに粒度分布のシャープな吸水性樹脂粉末が得られるので好ましい。
【００４９】
粉砕前に冷却を行う本発明では、従来より粒度分布がよりシャープであり、また、かかる粒度分布を得る為の粉砕時間も短くなり、且つ目的粒度以上の粗大な吸水性樹脂粉末が減少し、目的外の最大粒子や微粉末を分離する手間もなく、粗大粒子（例えば、８５０μｍオン品）の再粉砕や微粉（例えば、１５０μｍパス品）の再分級などのリサイクルの手間も減少するという効果も奏する。
冷却後に粉砕し分級した後の吸水性樹脂粉末は、次の工程にさらに保温ないし強制加熱することが好ましい。外部からの保温温度としては４０〜１００℃、さらには５０〜９０℃の範囲であり、吸水性樹脂粉末をかかる温度に保温することで、吸水性樹脂粉末の取り扱い性も向上し、製造工程での吸水性樹脂粉末の凝集や附着も防止される。本発明では、乾燥重合体を敢えて強制冷却して、粉砕ないし分級することで、乾燥効率や粉砕効率を向上させ、別途、さらに冷却後の吸水性樹脂粉末を保温ないし強制加熱（再加熱）すればよい。
【００５０】
なお、本発明で水性液、特に架橋剤水溶液を添加する場合、粉砕前に強制冷却して得られた吸水性樹脂粉末に対して、粉砕後にさらに強制冷却して温度を調整することが好ましい。温度の制御ないし冷却の手段は特に問わないが、粉砕後の吸水性樹脂粉末は流動性や比表面積が増大するため、前述の冷却手段がより適用でき、例えば、▲１▼冷却伝熱面を有し必要により攪拌される容器（ホッパー）や筒中に投入して強制冷却する方法、▲２▼連続ベルト上で十分に放冷する方法、▲３▼冷風を重合体に通気して強制冷却する方法、▲４▼冷えた空気を用いて輸送と同時に強制冷却する方法、▲５▼冷却伝熱面を有する低温スクリューコンベアーなどが用いられるが、少なくとも▲１▼の方法を用いることが好ましい。
【００５１】
すなわち、水性液添加前の吸水性樹脂粉末の温度は、前記強制冷却および必要によりさらなる保温や冷却によって、好ましくは８０〜３５℃、より好ましくは７０〜３５℃、さらに好ましくは６０〜３５℃、特に好ましくは５０〜３５℃の範囲に冷却（制御）された後、水性液が添加される。水性液添加前の吸水性樹脂粉末の温度が高いと水性液の混合が不均一になり、また、３５℃未満にまで強制冷却や放冷すると時間がかかるのみならず、冷却した粉末の凝集が見られたり、再加熱の際のエネルギーロスが大きくなり好ましくない。
上記して得られた吸水性樹脂粉末は粒度分布が優れている為、表面架橋することによって、さらに物性を改善するのに好適である。表面架橋には、以下の強制加熱を別途行えばよい。
【００５２】
すなわち、粉砕後や分級後の吸水性樹脂粉末の強制加熱工程を考えると、エネルギー的にも工程的にも一見無駄に見える本発明の強制冷却工程は、意外なことに、乾燥効率や粉砕効率を比較的に増大させ、また、得られた吸水性樹脂粉末への水性液の混合性も向上させたのである。
本発明で用いられる表面架橋剤としては、上記重合体が有する官能基と反応可能な化合物であれば、特に限定されるものではない。上記表面架橋剤としては、具体的には、例えば、プロピレングリコール、グリセリン、ブタンジオールなどの多価アルコール類、エチレングリコールジグリシジルエーテルなど多価エポキシ化合物（ポリ）エチレンイミン等の多価アミン化合物、アルキレンカーボネート化合物、多価オキサゾリン化合物、ハロエポキシ化合物やそのポリアミン付加物（ポリアミド−ポリアミドのエピハロヒドリン付加物；商標Kymene；ハーキュレス製）、モノ、ジまたはポリオキサゾリジノン化合物、多価金属等が挙げられるが、特に限定されるものではない。これら表面架橋剤は、一種類のみを用いてもよく、適宜、二種類以上を混合して用いてもよい。本発明で併用する場合、表面架橋剤のなかでも、溶解度パラメータ（ＳＰ値）が互いに異なる第一表面架橋剤および第二表面架橋剤を組み合わせてなる表面架橋剤（米国特許第５４２２４０５号参照）を用いることが、高加圧下（例えば、４．９０ｋPa以上）での吸収倍率に特に優れる吸水性樹脂粉末を得ることができるので好ましい。
【００５３】
上記表面架橋剤の使用量は、その種類や反応条件などで適宜決定されるが、通常、吸水性樹脂粉末の固形分１００重量部に対して、０．００１〜１０重量部、好ましくは０．０１〜５重量部、さらに好ましくは０．５〜４重量部の範囲で使用される。
上記重合体と表面架橋剤とを混合する際には、混合時あるいは混合後に、必要に応じて、水、水蒸気、または水と親水性有機溶媒とからなる水性液等を添加してもよい。この場合に使用される水の量は、用いる重合体の種類や粒径等にもよるが、吸水性樹脂粉末の固形分１００重量部に対して、１０重量部以下、好ましくは０．１〜１０重量部、より好ましくは１〜５重量部の範囲内である。
【００５４】
親水性有機溶媒としては、特に限定されるものではないが、具体的には、例えば、メチルアルコール、エチルアルコール、ｎ−プロピルアルコール、ｉｓｏ−プロピルアルコール、ｎ−ブチルアルコール、ｉｓｏ−ブチルアルコール、ｔ−ブチルアルコール等の低級アルコール類；アセトン等のケトン類；ジオキサン、テトラヒドロフラン等のエーテル類；Ｎ，Ｎ−ジメチルホルムアミド等のアミド類；ジメチルスルホキシド等のスルホキシド類等が挙げられる。
上記重合体と表面架橋剤とを混合する際には、例えば、上記の水性液中に重合体を分散させた後、表面架橋剤を混合してもよく、水や水性液に溶解させた表面架橋剤を、重合体に直接、噴霧若しくは滴下して混合してもよい。また、水を用いて混合する場合には、水に不溶な微粒子状の粉体や、各種有機酸や無機酸、界面活性剤等を共存させてもよい。これらの混合方法の中では噴霧混合が好ましく、その際の水性液は５００μｍ以下、さらには３００μｍ以下の微細の液滴で添加される。
【００５５】
また、本発明において、水性液を添加する場合、混合機の内壁は室温を超える温度を有していることが好ましく、混合機の内壁温度が４０℃以上、好ましくは４５〜１００℃、さらに好ましくは５０〜９５℃、より好ましくは５５〜９０℃に保たれていること、また、内壁温度が水性液添加前の吸水性樹脂粉末より高温、好ましくは４０℃以下、さらには２０℃以下、特に１０℃以下の高温であることが好ましい。なお、本発明で内壁とは攪拌翼を含めた混合機内面のことであり、これら温度は連続混合の場合、定常状態での温度で制御すること、特に金属部分は必須に制御することが好ましい。
【００５６】
混合機の内壁温度が室温以下である場合、粉末の温度を制御しても、水性液を添加した吸水性樹脂粉末が内壁に付着したり、得られた吸水性樹脂粉末の物性低下が起こる恐れがあり、また、内壁温度が高すぎる場合、水溶液中の架橋剤などが潰れたり、水性液の混合が不均一になる恐れがある。
混合機の内壁温度の制御は、上記温度の制御できれば制限はないが、例えば、▲１▼温風や熱媒などの外部加熱によって制御してもよいし、また、混合機自体に十分に保温できる構造を持たせた上で、さらに、▲２▼特定温度の粉末や水性液の混合を連続かつ多量（例えば、５００ｋｇ／ｈｒ以上）に混合することで混合機内壁を制御してもよいし、▲３▼水性液添加による吸水性樹脂粉末の水和熱や混合時の摩擦熱を用いて制御してもよいし、これらを併用してもよいが、好ましくは、▲１▼が用いられる。
【００５７】
さらに、かかる方法において、特定内壁温度を有する混合機は、攪拌翼を有する高速攪拌型混合機であることが好ましく、通常、その回転数は１０ｒｐｍ以上、好ましくは１００〜１００００ｒｐｍ、より好ましくは３００〜５０００ｒｐｍ、最も好ましくは５００〜３０００ｒｐｍで攪拌混合され、その攪拌時間は通常５分以内、好ましくは３分以内、さらに好ましくは１分以内、より好ましくは０．２分以内である。また、混合機として攪拌翼を複数有する気流攪拌型混合機がより好ましい。
本発明の方法において、混合性改良による物性改良が大きいことから、水性液が架橋剤水溶液であることが好ましく、特に、従来、吸水性樹脂への混合が困難であった架橋剤水溶液が必要により、多価アルコール以外の架橋剤を含む多価アルコール水溶液、特に多価アルコールのみを架橋剤とする水溶液である場合、および／または、水性液が多価アルコール以外の有機溶媒、特に揮発性有機溶媒を含有しない場合、本発明の効果は飛躍的に発揮されるので好ましい。また、混合機の内壁温度を高める場合、本発明の水性液添加は、内壁温度でも不活性な架橋剤、例えば、再加熱に必要な反応温度１１０℃以上の架橋剤、特に多価アルコールに好適に適用される。また、本発明で多価アルコールは架橋剤として用いてもよいし、反応温度以下で用いることで架橋剤の溶媒としてもよいし、それらの働きを併用させてもよい。なお、用いられる多価アルコール以外の架橋剤は、前述の架橋剤や後述の先行文献に例示される。物性面から本発明の効果を最も顕著に表す多価アルコールとしては、たとえば、炭素数３〜８の多価アルコールが挙げられ、さらにはグリセリン、プロピレングリコール、ブタンジオール、ペンタンジオール、ヘキサンジオールから選ばれる少なくとも１種の多価アルコール（なお、ジオールの置換位置は問わない）が好ましく用いられる。
【００５８】
なお、本発明でいう揮発性有機溶媒とはその沸点が後述の架橋反応の温度以下の溶媒であり、特に沸点が１００℃以下、さらには沸点８５℃以下の有機溶媒をさし、本発明では、これら有機溶媒を使用せず水性液を添加することで環境面、コスト面、安全性の面でも優れた吸水性樹脂が得られるので好ましい。
本発明においては、上記重合体と表面架橋剤とを混合した後、架橋剤の種類により、必要に応じて強制加熱を行い、重合体の表面近傍を架橋させる。強制加熱の温度は、用いる表面架橋剤にもよるが、好ましくは１００℃以上、より好ましくは１１０〜２３０℃、さらに好ましくは１６０〜２２０℃であり、強制加熱の時間は適宜決定されるが、好ましくは１〜１２０分、よりに好ましくは５〜６０分の範囲である。また、強制過熱に用いられる装置としては、例えば、溝型混合乾燥機、ロータリー乾燥機、ディスク乾燥機、流動層乾燥機、気流型乾燥機、赤外線乾燥機等が挙げられる。なお、これら加熱装置は前記混合装置とは別個に設け、それらが互いに連結されることが好ましい。
【００５９】
なお、これらの表面架橋方法は、欧州特許０３４９２４０号、同０６０５１５０号、同０４５０９２３号、同０８１２８７３号、同０４５０９２４号、同０６６８０８０号などの各種欧州特許や、日本国特開平７−２４２７０９号、同７−２２４３０４号などの各種日本特許、米国特許５４０９７７１号、同５５９７８７３号、同５３８５９８３号、同５６１０２２０号、同５６３３３１６号、同５６７４６３３号、同５４６２９７２号などの各種米国特許、国際公開特許ＷＯ９９／４２４９４号、ＷＯ９９／４３７２０号、ＷＯ９９／４２４９６号などの各種国際公開特許にも記載されており、これらの表面架橋方法も本発明での再加熱や水性液の添加に適用できる。
【００６０】
以上、本発明は、架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕して得られた粉末に混合機中で水性液を添加する吸水性樹脂粉末の製造方法であって、加熱乾燥温度が１１０〜２３０℃の範囲であること、水性液添加前に乾燥重合体を８０〜３５℃に強制冷却すること、および、粉砕後の乾燥重合体の嵩比重（ＪＩＳ Ｋ ３３６２に準じて測定）を０．６５ｇ／ｍｌ以上とすることを特徴とする吸水性樹脂粉末の製造方法をも提供する。
また、本発明は、架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕して得られた粉末に混合機中で水性液を添加する吸水性樹脂粉末の製造方法であって、加熱乾燥温度が１１０〜２３０℃の範囲であること、水性液添加前に乾燥重合体を８０〜３５℃に強制冷却すること、および、混合機の内壁温度が４０℃以上の攪拌混合機であること、および、１１０〜２３０℃に再加熱することを特徴とする吸水性樹脂粉末の製造方法をも提供する。
【００６１】
なお、これら２つの方法において、乾燥温度と冷却温度の差が大きいほど、本発明の効果は顕著であり、好ましい温度範囲などは前述の通りである。
こうして得られた吸水性樹脂粉末の加圧下吸収倍率（１．９６ｋPa）や無荷重下吸水倍率（生理食塩水）は好ましくは２５ｇ／ｇ以上、より好ましくは２７ｇ／ｇ以上、さらに好ましくは３０ｇ／ｇ以上、特に好ましくは３５ｇ／ｇ以上である。また、その水可溶成分や粒子径、嵩比重、吸水倍率などは前述の範囲である。
さらに、加圧下吸収倍率（４．９０ｋPa）は、好ましくは２３ｇ／ｇ以上、より好ましくは２５ｇ／ｇ以上、さらに好ましくは２７ｇ／ｇ以上である。本発明ではかかる高物性の吸水性樹脂粉末が容易に安定的に製造できる。
【００６２】
また、本発明にかかる吸水性樹脂粉末の製造方法は、
架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕する吸水性樹脂粉末の製造方法であって、
加熱乾燥後の乾燥重合体を強制冷却すること、
乾燥重合体を粉砕して嵩比重（ＪＩＳ Ｋ ３３６２に準じて測定）０．６５ｇ／ｍｌ以上の吸水性樹脂粉末とすること、
冷却された吸水性樹脂粉末をさらに表面架橋すること、
を特徴とする。
【００６３】
また、本発明にかかる吸水性樹脂粉末の製造方法は、
架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕する吸水性樹脂粉末の製造方法であって、
加熱乾燥後の乾燥重合体を強制冷却すること、
乾燥重合体を粉砕して嵩比重（ＪＩＳ Ｋ ３３６２に準じて測定）０．６５ｇ／ｍｌ以上の吸水性樹脂粉末とすること、
冷却された吸水性樹脂粉末にさらに水性液を添加すること、
水性液が内壁が加熱された攪拌混合機で添加されること、
を特徴とする。
【００６５】
以上して得られた本発明の吸水性樹脂粉末に、さらに、必要に応じて、消臭剤、抗菌剤、香料、各種の無機粉末、発泡剤、顔料、染料、親水性短繊維、可塑剤、粘着剤、界面活性剤、肥料、酸化剤、還元剤、キレート剤、酸化防止剤、水、水溶性高分子、バインダー、塩類等を添加して、種々の機能を付与してもよい。
本発明の製造方法を含んで得られる吸水性樹脂粉末は、粒度分布および物性に優れてるため、表面架橋やその後中和などでさらに高物性を発揮する吸水性樹脂粉末とすることができる。また、本発明では、かかる吸水性樹脂粉末を生産性高く簡便に、製造工程での附着や凝集なく、低エネルギーコストで安価に得ることができる。
【００６６】
このため、本発明の吸水性樹脂粉末は広い用途に使用できるが、特に、紙おむつ／生理用ナプキンなどの衛生材料／吸収物品に好適であり、粉砕パルプ等の親水性繊維材料と複合化され衛生材料として好ましく使用することができる。また、本発明の吸水性樹脂粉末は高物性であるため、衛生材料中でコア濃度（繊維および吸水性樹脂粉末の合計量に対する吸水性樹脂粉末の重量比）が高い衛生材料で好適に使用することができ、例えば、吸水性樹脂粉末が３０〜１００重量％、好ましくは４０〜９５重量％以上、さらには５０〜９０重量％濃度の衛生材料で好適に使用することができる。
【００６７】
【実施例】
本発明を実施するための最良の形態
以下、実施例および比較例により、本発明をさらに詳細に説明するが、本発明はこれらにより何ら限定されるものではない。尚、吸水性樹脂粉末の諸性能は、以下の方法により測定した。また、実施例の重合・乾燥・粉砕などは、実生産をシュミレートした一連の連続操作で行った。
（ａ）無荷重での吸水倍率
吸水性樹脂粉末０．２００ｇを不織布製の袋（６０ｍｍ×６０ｍｍ）に均一に入れヒートシールした後、大過剰（約２００ｇ）の０．９重量％生理食塩水に室温で浸漬した。浸漬６０分後に袋を引き上げ、遠心分離機を用いて ２５０Ｇで３分間水切りを行った後、袋の重量Ｗ１（ｇ）を測定した。また、同様の操作を吸水性樹脂粉末を用いないで行い、そのときの重量Ｗ０（ｇ）を測定した。そして、これら重量Ｗ１とＷ０から、次式（ａ）に従って無荷重での吸水倍率（ｇ／ｇ）を算出した。
【００６８】
無荷重での吸水倍率（ｇ／ｇ）
＝（重量Ｗ１（ｇ）−重量Ｗ０（ｇ）−０．２）／０．２（ｇ）
（ｂ）水可溶成分量
吸水性樹脂粉末１．０００ｇを１８４．３ｇの生理食塩水中に膨潤分散させ、２００ｍｌビーカー中で１６時間攪拌した後、濾紙で膨潤ゲルを分離して濾過した。次いで、得られた濾液を０．１Ｎ(0.1mol/l)水酸化ナトリウム水溶液および０．１Ｎ(0.1mol/l)塩酸水溶液を用いてカルボキシル基を中和滴定することで、吸水性樹脂粉末（膨潤ゲル）中より溶解している濾液中の水溶性ポリマー（＝水溶性ポリアクリル酸（塩））、すなわち、吸水性樹脂粉末の水可溶成分量（重量％）を算出した。
【００６９】
（ｃ）吸水性樹脂の固形分
乾燥重合体より得られた吸水性樹脂粉末１．０００ｇをアルミカップ（内径５３ｍｍ×高さ２３ｍｍ）に入れ１８０℃の無風オーブンで３時間再乾燥し、その乾燥減量（ｇ）より吸水性樹脂粉末（ないし乾燥重合体）の固形分（重量％）を算出した。なお、乾燥重合体については、粉砕後にその固形分を上記と同様の方法により測定することで、乾燥重合体の固形分とした。
（ｄ）粒度分布および平均粒子径
吸水性樹脂粉末をＪＩＳ標準篩（８５０μｍ、６００μｍ、３００μｍ、１５０μｍ）で分級して、篩ごとの各粒度（８５０μｍオン品／８５０〜６００μｍ／６００〜３００μｍ／３００〜１５０μｍ／１５０μｍパス品）の重量を測定した。また、必要によりＪＩＳ標準篩を追加して、求めた各粒度の粒度分布を対数確率紙にプロットすることで、その重量平均粒子径（Ｄ５０）を求めた。
【００７０】
（ｅ）加圧下吸収倍率
欧州特許０８８５９１７号、欧州特許０８１７８７３号および欧州特許０８１１６３６号の実施例に開示の方法にしたがって、吸水性樹脂粉末の生理食塩水に対する５０ｇ／ｃｍ2（約４．９０ｋＰａに相当）での加圧下吸収倍率を測定した。
すなわち、吸水性樹脂粉末０．９００ｇに対して５０ｇ／ｃｍ２（約４．９０ｋＰａ）の荷重を均一に加えながら、室温で６０分間にわたって吸水性樹脂粉末が吸収した生理食塩水の重量Ｗ２（ｇ）を、天秤を用いて測定した。そして、上記の重量Ｗ２から、次式ｂに従って、吸収開始から６０分後の加圧下の吸水倍率（ｇ／ｇ）を算出し、５０ｇ／ｃｍ2（約４．９０ｋＰａ）での加圧下吸収倍率とした。
【００７１】
式ｂ；加圧下吸収倍率 （ｇ／ｇ）＝重量Ｗ２(ｇ) ／吸水性樹脂粉末の重量（ｇ）
なお、同様の測定において、荷重を２０ｇ／ｃｍ２（約１．９６ｋＰａに相当）で測定する場合、加圧下吸水倍率（１．９６ｋＰａ）と称する。
（ｆ）嵩比重
嵩比重測定器（蔵持科学器機製作所社製）を用い、ＪＩＳ Ｋ ３３６２に準じて測定した。（なお、嵩比重の測定法として、欧州特許出願１０２９８８６号／特願２０００−３５９４１号も参照。）
すなわち、温度は２５±２℃、相対湿度は３０〜５０％の部屋で、吸水性樹脂粉末１２０ｇをダンパーを閉めた漏斗に入れた後、速やかにダンパーを開け、試料を受器（１００ｍｌ）に落とした。受器から盛り上がった試料は、ガラス棒ですり落とした後、試料の入った受器の重さ（ｇ）を０．１ｇまで正確に量り、嵩比重（ｇ／ｍｌ）を算出した。
【００７２】
（ｇ）耐衝撃性
吸水性樹脂粉末の耐衝撃性を欧州特許０８１７８７３号（米国特許６０７１９７６号）に従い、ガラス容器に入れた粉末３０．０ｇをガラスビーズ１０．０ｇともに３０分間振動させた後、その加圧下吸収倍率の低下を評価した。
（ｈ）含水ゲル状架橋重合体の重量平均粒子径
含水ゲル状架橋重合体（含水ゲル）がごく一部しか膨潤も収縮もしない、２０重量％食塩水を用いて粒度分布を測定した。すなわち、３０ｇの含水ゲルを２０重量％食塩水１０００ｇに分散させ、スターラーチップを用いて３００ｒｐｍで２時間攪拌した。２時間後に分散液を６段重ねのＪＩＳ標準篩（目開きが９５００μｍ、２０００μｍ、８５０μｍ、６００μｍ、３００μｍ、７５μｍ／ＪＩＳ・Ｚ８８０１／ステンレス製篩／内径２０ｃｍ）に投入し、さらに６０００ｇの２０重量％食塩水を用いて順次注ぐことで含水ゲルを分級した。次いで、篩の裏面側を紙で十分に水切りした後、含水ゲルの各粒度の重量を求め、総重量（ｇ）と初めの重量（３０ｇ）から膨潤倍率を求め、各粒度（μｍ）の膨潤前の粒度（μｍ）に換算して対数確率紙にプロットすることで、含水ゲルの重量平均粒子径Ｄ５０を求めた。
【００７３】
（製造例１）…未中和ポリアクリル酸架橋体の重合および乾燥
アクリル酸１０６６．６１ｇ、共重合性架橋剤としてＮ，Ｎ‘−メチレンビスアクリルアミド９．１２ｇ、および水４２８０．１１ｇからなる単量体水溶液（１）を窒素ガスで６０分脱気後、開閉可能な密閉重合容器中に仕込んだ。
次いで、容器上部を窒素気流下の状態とし、２３℃の液温にて、重合開始剤として２，２´−アゾビス（２−アミジノプロパン）２塩酸塩の１０重量％水溶液を３２．２７ｇ、過酸化水素の１０重量％水溶液を１０．６６ｇ、およびＬ−アスコルビン酸の１重量％水溶液を２６．６４ｇ、をそれぞれ添加したところ、約５分後に重合が開始し、その後、１時間の静置重合を行った。得られた重合体を容器から取出し、孔径７．５ｍｍのミートチョパー（平賀製作所製）で数ｍｍの粒子状に細分化することで、平均粒子径１５００μｍの粒子状の含水ゲル状架橋重合体（１）を得た。
【００７４】
次いで、粒子状の含水ゲル状架橋重合体（１）を層厚約５０ｍｍにて目開き３００μｍの金網に広げて積層し、次いで、ゲルの上下方向に１３５℃（露点６５℃）の熱風を１ｍ／秒、１時間通気させることで、熱風乾燥を行った。こうして、固形分９５重量％で粒子状の乾燥重合体（１）からなるブロック状物を得、その材料温度は約１３５℃であった。
（製造例２）…部分中和ポリアクリル酸架橋体の重合および乾燥
アクリル酸６７３．７９ｇ、アクリル酸ナトリウムの３７重量％水溶液５９０４．７ｇ、内部架橋剤としてポリエチレングリコールジアクリレート（平均ポリエチレングリコールユニット数８）１５．８７ｇおよび水７１４．２ｇからなる単量体水溶液（２）を窒素ガスで６０分脱気後、内容量１０Ｌでシグマ型羽根を２本有するジャケット付きステンレス製双腕型ニーダーに蓋を付けた反応器に該水溶液を供給し、２０℃の温度に保ちながら反応系の窒素置換を続けた。
【００７５】
次いで、羽根を回転させながら過硫酸ナトリウムの２０重量％水溶液１９．５５ｇとＬ−アスコルビン酸の１．０重量％水溶液１．４７ｇを添加したところ、１分後に重合が開始し、２０分後に反応系はピーク温度に達した。その際生成した含水ゲル架橋重合体は約５ｍｍのサイズに細分化されていた。その後更に攪拌を続け、重合を開始して６０分後に、平均粒子径１６００μｍの粒子状の含水ゲル架橋重合体（２）を取り出した。
次いで、粒子状の含水ゲル状架橋重合体（２）を層厚約５０ｍｍにて目開き３００μｍの金網に広げて積層し、次いで、ゲルの上下方向に１７０℃の熱風（露点５０℃）を１ｍ／秒、１時間通気させることで、熱風乾燥を行った。こうして、固形分９６重量％で粒子状の乾燥重合体（２）からなるブロック状物を得、その材料温度は約１７０℃であった。
【００７６】
（製造例３）…部分中和ポリアクリル酸架橋体の重合および乾燥
製造例２において、単量体水溶液（２）に代えて、アクリル酸４２５．１ｇ、アクリル酸ナトリウムの３７重量％水溶液４４９７．２ｇ、内部架橋剤としてトリメチロールプロパントリアクリレート１．４０ｇおよび水５７７．７ｇからなる単量体水溶液（３）を用いる以外は、製造例２と同様にニーダー中で水溶液重合を行うことで、平均粒子径１７００μｍの粒子状の含水ゲル架橋重合体（３）を得た。
次いで、製造例２と同様に粒子状の含水ゲル状架橋重合体（３）を１７０℃で１時間の熱風乾燥を行った。こうして、固形分９５重量％で粒子状の乾燥重合体（３）からなるブロック状物を得、その材料温度は約１７０℃であった。
【００７７】
（製造例４）…部分中和ポリアクリル酸架橋体の重合および乾燥
製造例２において、単量体水溶液（２）に代えて、アクリル酸３６９ｇ、アクリル酸ナトリウムの３７重量％水溶液３９０７ｇ、内部架橋剤としてポリエチレングリコールジアクリレート（平均ポリエチレングリコールユニット数ｎ＝８）４．９９ｇおよび水１２１６ｇからなる単量体水溶液（４）を用いる以外は、製造例２と同様にニーダー中で水溶液重合を行うことで、平均粒子径１７００μｍの粒子状の含水ゲル架橋重合体（４）を得た。
次いで、粒子状の含水ゲル架橋重合体（４）を製造例２と同様に連続熱風乾燥を行った。こうして、固形分９５重量％で粒子状の乾燥重合体（４）からなるブロック状物を得、その材料温度は約１７０℃であった。
【００７８】
（製造例５）…部分中和ポリアクリル酸架橋体の重合および乾燥
アクリル酸１００部、３７重量％アクリル酸ナトリウム水溶液６５６．４部、ポリエチレングリコールジアクリレート（平均ポリエチレングリコールユニット数ｎ＝８）０．７７部、および、脱イオン水２１６．７部を十分混合し、単量体水溶液（５）を作成した。得られた単量体水溶液（５）を定量ポンプで２９０ｋｇ／ｈの連続フィードを行い、配管の途中では窒素ガスを連続的に吹き込み、単量体水溶液（５）の酸素濃度を０．５ｐｐｍ以下にした。単量体水溶液（５）にさらに２，２´−アゾビス（アミジノプロパン）２塩酸塩（商品名Ｖ−５０、和光純薬工業社製）、過硫酸ナトリウム、Ｌ−アスコルビン酸、過酸化水素の開始剤水溶液を４種類順次ラインミキシング（開始剤固形分(成分)で０．０８部／０．０８部／０．００８部／０．００６部）して、１２ｃｍ／分で移動するスチール製のエンドレスベルト重合機（両サイドに５０ｍｍの堰を有する平面ベルトを有する）に厚み２５ｍｍとなるように連続供給した。即座に重合が開始し、こうして得られた重合体をベルト重合機の末端から排出して、さらに連続裁断機で約５〜１０ｃｍ片に裁断した後、ミートチョッパー（孔径９ｍｍ）で粉砕することにより、平均粒子径１６００μｍの粒子状含水ゲル状架橋重合体（５）を得た。
【００７９】
次いで、粒子状含水ゲル状架橋重合体（５）をパンチングメタル上に厚み５０ｍｍに積載し、ベルト式乾燥機で連続式熱風乾燥（１８０℃の熱風（露点６０℃）を上下方向に２０分間）を行った。こうして、固形分９４重量％で粒子状の乾燥重合体（５）からなるブロック状物が得られ、その材料温度は約１８０℃であった。
（実施例１）…乾燥重合体（１）の６０℃への強制冷却
製造例１で得られた、粒子状の乾燥重合体（１）のブロック状物（材料温度約１３５℃）に対して、熱風に代えて、上下方向に室温の冷風（１ｍ／秒）を通気する事で粒子状の乾燥重合体（１）のブロック状物を６０℃に強制冷却した後、風冷式冷却装置から取り出した。取り出したと同時に金網上のブロック状凝集物を解砕し、３０秒以内に、得られた粒子状乾燥物（１）を３段ロールグラニュレーター（ロールギャップが上から１．０ｍｍ／０．４５ｍｍ／０．２５ｍｍ）で連続的に粉砕した。乾燥の際、乾燥重合体（１）のブロック状物の目開き３００μｍ金網からの剥離性は非常に良好であり、粉砕によって得られた吸水性樹脂粉末（１）の粒度分布を表１に示す。
【００８０】
（実施例２）…同４５℃への強制冷却
実施例１において、冷風の通気する時間を調整することで、ブロック状物を４５℃に強制冷却した後、実施例１と同様に解砕し、得られた粒子状乾燥物（２）を同様に粉砕した。乾燥の際、乾燥重合体（１）のブロック状物の目開き３００μｍ金網からの剥離性は非常に良好であり、粉砕によって得られた吸水性樹脂粉末（２）の粒度分布を表１に示す。
（実施例３）…同９５℃への強制冷却
実施例１において、冷風の通気する時間を調整することで、ブロック状物を９５℃に強制冷却した後、実施例１と同様に解砕し、得られた粒子状乾燥物（３）を同様に粉砕した。乾燥の際、乾燥重合体（１）のブロック状物の目開き３００μｍ金網からの剥離性は実施例１，２より若干悪いが良好であり、粉砕によって得られた吸水性樹脂粉末（３）の粒度分布を表１に示す。
【００８１】
（実施例４）…同８０℃への強制冷却
実施例１において、冷風の通気する時間を調整することで、ブロック状物を８０℃に強制冷却した後、実施例１と同様に解砕し、得られた粒子状乾燥物（４）を同様に粉砕した。乾燥の際、乾燥重合体（１）のブロック状物の目開き３００μｍ金網からの剥離性は実施例１，２より若干悪いが良好であり、粉砕によって得られた吸水性樹脂粉末（４）の粒度分布を表１に示す。
（実施例５）…乾燥重合体（２）の４０℃への強制冷却
製造例２で得られた、粒子状の乾燥重合体（２）のブロック状物（材料温度約１７０℃）に対して、熱風に代えて、上下方向に室温の冷風（１ｍ／秒）を通気する事で粒子状の乾燥重合体（２）のブロック状物を４０℃に強制冷却した後、風冷式冷却装置から取り出した。取り出したと同時に金網上のブロック状凝集物を解砕し、３０秒以内に、得られた粒子状乾燥物（５）を３段ロールグラニュレーター（ロールギャップが上から１．０ｍｍ／０．４５ｍｍ／０．２５ｍｍ）で連続的に粉砕した。乾燥の際、乾燥重合体（２）のブロック状物の目開き３００μｍ金網からの剥離性は非常に良好であり、また、粉砕によって得られた吸水性樹脂粉末（５）の粒度分布を表１に示す。
【００８２】
（実施例６）…水性液添加と再加熱
強制冷却工程を含んで得られた吸水性樹脂粉末（５）１００重量部に、粉温３５℃にて、１，４−ブタンジオール／プロピレングリコール／水／イソプロパノール＝０．３２／０．５０／２．７３／０．４５（重量部）からなる表面架橋剤の溶液を混合し、さらに、２１０℃で３０分間の再加熱することで、表面架橋された吸水性樹脂粉末（６）を得た。吸水性樹脂粉末（６）の無荷重での吸水倍率は２８ｇ／ｇであり、加圧下吸水倍率（４．９０ｋＰａ）は２５ｇ／ｇであった。
【００８３】
なお、実施例５で得られた吸水性樹脂粉末（５）について、その無荷重での吸水倍率と水可溶成分量を測定したところ、それぞれ３１ｇ／ｇ、５重量％であった。また、水性液添加前の吸水性樹脂粉末（５）の嵩比重は０．６７ｇ／ｍｌで、温度は３５℃であった。
（実施例７）…後中和
実施例１で得られた吸水性樹脂粉末（１）と所定量の炭酸ソーダ粉末とをドライブレンド（粉体混合）することによりカルボキシル基を後中和することで、７５モル％中和の吸水性樹脂粉末（７）を得た。吸水性樹脂粉末（７）の無荷重での吸水倍率は４２ｇ／ｇであり、水可溶成分量は３重量％であった。
【００８４】
さらに実施例２〜４で得られた吸水性樹脂粉末（２）〜（４）も同様に後中和したところ、無荷重での吸水倍率は４２ｇ／ｇで、水可溶成分量は３重量％であった。
（比較例１）…強制冷却なし
実施例１において、製造例１で得られた乾燥重合体（１）に冷風の通気を用いることなく、乾燥機から取り出したと同時に、ブロック状物を実施例１と同様に解砕し、得られた比較粒子状乾燥物（１）（粉砕時は温度１２０℃）を同様に粉砕した。乾燥の際、乾燥重合体（１）のブロック状物の目開き３００μｍ金網からの剥離性は悪く、乾燥重合体（１）粒子の金網への目詰まりが見られ、連続乾燥する際の乾燥効率（均一性や乾燥速度）が低下していった。粉砕によって得られた比較吸水性樹脂粉末（１）の粒度分布を表１に示す。
【００８５】
（比較例２）…強制冷却なし
実施例５において、製造例２で得られた乾燥重合体（２）に冷風の通気を用いることなく、乾燥機から取り出したと同時に、ブロック状物を実施例１と同様に解砕し、得られた比較粒子状乾燥物（２）（粉砕時は温度１２０℃）を同様に粉砕した。乾燥の際、乾燥重合体（２）のブロック状物の目開き３００μｍ金網からの剥離性は悪く、乾燥重合体（２）粒子の金網への目詰まりが見られ、連続乾燥する際の乾燥効率（均一性や乾燥速度）が低下していた。また、粉砕によって得られた比較吸水性樹脂粉末（２）の粒度分布を表１に示す。
【００８６】
（比較例３）…水性液添加と後加熱／ただし強制冷却なし
比較例２（乾燥重合体（２）の強制冷却なし）で得られた比較吸水性樹脂粉末（２）に対して、実施例６（同重合体の強制冷却あり）と同様に水性液を添加した。３５〜８０℃に冷却しない比較吸水性樹脂粉末（２）では、吸水性樹脂粉末（５）と同じ粒度に調整しても、粉温が高いため、混合機中での凝集や付着が徐々に見られ、連続混合が困難であった。
（実施例８）…乾燥重合体（３）の強制冷却
製造例３で得られた、粒子状の乾燥重合体（３）のブロック状物（材料温度約１７０℃）に対して、熱風に代えて、上下方向に室温の冷風（１ｍ／秒）を通気する事で粒子状の乾燥重合体（３）のブロック状物を５０℃に強制冷却した後、風冷式冷却装置から取り出した。取り出したと同時に金網上のブロック状の凝集物を解砕し、３０秒以内に、得られた粒子状乾燥物（６）を３段ロールグラニュレーター（ロールギャップが上から１．０ｍｍ／０．４５ｍｍ／０．１０ｍｍ）で連続的に粉砕した。乾燥の際、乾燥重合体（３）のブロック状物の目開き３００μｍ金網からの剥離性は非常に良好であり、また、粉砕によって得られた吸水性樹脂粉末（８）の粒度分布を表１に示す。なお、吸水性樹脂粉末（８）の無荷重での吸水倍率は４４ｇ／ｇであり、水可溶成分量は１７重量％であった。
【００８７】
（実施例９）…同・粉砕条件の変更
実施例８において、乾燥重合体（６）の粉砕条件を変更した。すなわち、粒子状乾燥物（６）の粉砕をピンミル（不二パウダル工業製サンプルミルＫII−１）で粉砕（８５０〜１５０μｍが８５重量％）し、さらにモホジナイザー（日本精機社製、高速ホモジナイザー；ＭＸ−７）で表面を研磨することで吸水性樹脂粉末（９）を得た。粒度分布を表１に示す。
（実施例１０）…嵩比重０．７４ｇ／ｍｌへの水性液添加
実施例９で得られた吸水性樹脂粉末（９）を３００〜１５０μｍに分級した温度４０℃の吸水性樹脂粉末（９Ａ）（嵩比重０．７４ｇ／ｍｌ）１００重量部に対して、プロピレングリコール／水／エタノール＝０．３／２．５／１（重量部）からなる水性液を高速混合機中で噴霧添加して、さらに２１０℃のオイルバス中で攪拌し３０分間加熱処理することで、表面架橋された吸水性樹脂粉末（１０）を得た。その無荷重下での吸水倍率、加圧下吸収倍率（1.96kPa）、同（4.90kPa）を表２に示す。さらに、耐衝撃性試験後の加圧下吸収倍率の値を（ ）で示す。
【００８８】
（実施例１１）…嵩比重０．６３ｇ／ｍｌへの水性液添加
実施例８で得られた吸水性樹脂粉末（８）を３００〜１５０μｍに分級した温度４０℃の吸水性樹脂粉末（８Ａ）（嵩比重０．６３ｇ／ｍｌ）に対して、実施例１０と同様に水性液を添加し、さらに３０分間加熱処理した。得られた吸水性樹脂粉末（１１）の分析結果を表２に示す。
（実施例１２）…嵩比重０．７３ｇ／ｍｌへの水性液添加
実施例９で得られた吸水性樹脂粉末（９）を５００〜１５０μｍに分級した温度４０℃の吸水性樹脂粉末（９Ｂ）（嵩比重０．７３ｇ／ｍｌ）１００重量部に対して、実施例１０，１１と同様に水性液を添加して、さらに２５分間加熱処理した。得られた吸水性樹脂粉末（１２）の分析結果を表２に示す。
【００８９】
（実施例１３）…嵩比重０．６３ｇ／ｍｌへの水性液添加
実施例８で得られた吸水性樹脂粉末（８）を５００〜１５０μｍに分級した温度４０℃の吸水性樹脂粉末（８Ｂ）（嵩比重０．６３ｇ／ｍｌ）に対して、実施例１０〜１２と同様に水性液を添加し、さらに２５分間加熱処理した。得られた吸水性樹脂粉末（１３）の分析結果を表２に示す。
（実施例１４）…乾燥重合体（４）の強制冷却
製造例４で得られた、粒子状の乾燥重合体（４）のブロック状物（材料温度約１７０℃）に対して、熱風に代えて、上下方向に室温の冷風（１ｍ／秒）を通気する事で粒子状の乾燥重合体（４）のブロック状物を６５℃に強制冷却した後、風冷式冷却装置から取り出した。取り出したと同時に金網上のブロック状の凝集物を解砕し、３０秒以内に、得られた粒子状乾燥物（８）を３段ロールグラニュレーター（ロールギャップが上から１．０ｍｍ／０．４５ｍｍ／０．０９ｍｍ）で連続的に粉砕した。なお、乾燥の際、乾燥重合体（４）のブロック状物の目開き３００μｍ金網からの剥離性は非常に良好であった。得られた吸水性樹脂粉末（１４）の無荷重での吸水倍率は４３ｇ／ｇであり、水可溶成分量は１０重量％であり、その粒度分布を表１に示す。
【００９０】
（実施例１５）…水性液添加と後加熱／粉温６０℃
実施例１４で得られた温度６０℃の吸水性樹脂粉末（１４）５００ｇに、エチレングリコールジグリシジルエーテル／プロピレングリコール／水＝０．１／３／１（重量％）からなる水溶液を、外部加熱により内壁温度を６０℃に制御したレディゲ混合機（M5R；Lodige社製）中で高速混合（回転数３２０ｒｐｍ）したところ、有機溶媒を使用せずとも、吸水樹脂粉末の付着は殆どなく連続混合できた。さらに混合物を２０５℃のオイルバス中で、５Ｌモルタルミキサー（西日本製作所製）で５０分攪拌加熱しすることで、表面架橋された吸水性樹脂粉末（１５）を得た。結果を表２に示す。
【００９１】
（実施例１６）…水性液添加と後加熱／粉温４０℃
実施例１４で得られた温度６０℃の吸水性樹脂粉末（１４）に対して、連続的に風冷して温度を４０℃にまで冷却した。以下、温度４０℃の吸水性樹脂粉末（１４）を用いて、以下、実施例１５と同様に同様に水性液を添加したところ、混合機への付着はさらに低減した。得られた混合物を実施例１２と同様に加熱処理するころで吸水性樹脂粉末（１６）を得た。その分析結果を表２に示す。
（実施例１７）…水性液添加と後加熱／混合機内壁が室温
実施例１４において、混合機の外部加熱を中止して室温の混合機で水性液を添加した、内壁への付着が大幅に増加し連続操業性が低下した。
【００９２】
（実施例１８）…乾燥重合体（５）の強制冷却
製造例５で得られた、粒子状の乾燥重合体（５）からなるブロック状物（材料温度約１８０℃）に対して、熱風に代えて、室温の冷風（１ｍ／ｓ）を上下方向に連続供給することで、粒子状の乾燥重合体（５）のブロック状物を６０℃に強制冷却した後、連続ベルト風冷式冷却装置から取り出し、さらに、乾燥重合体（５）を１００ｋｇ／ｈでロール粉砕機に連続供給することで、連続重合・連続乾燥・連続粉砕を行った。乾燥の際、乾燥重合体（５）のパンチングメタルからの剥離性は非常に良好であり、粉砕によって得られた吸水性樹脂粉末（１８）の粒度分布を表１に示す。吸水性樹脂粉末（１８）の無荷重での吸水倍率は５５ｇ／ｇで、水可溶分は６重量％であった。
【００９３】
また、粒子状の乾燥重合体（５）のブロック状物の強制冷却に用いられた冷風は、この強制冷却への使用により、約９０℃に加熱されていたので、その温風を配管を通じて製造例５のベルト熱風乾燥機の空気供給口に供給して、乾燥に用いる熱風（１８０℃）の原料として、製造例５の連続乾燥を行った。こうして、製造例５の熱風乾燥では室温の空気を用いるに代わり、約９０℃の温風を用いて１８０℃の熱風を製造しているため、その分、大きな省エネルギーとなり、かつ、温風（排ガス）を環境中に排出しないという利点を有する。
（実施例１９）…水性液添加と後加熱／粉温５０℃
実施例１８で強制冷却工程を経て得られた吸水性樹脂粉末（１８）を粉温５０℃で高速連続混合機（タービュライザー／１０００ｒｐｍ）に１００ｋｇ／ｈで供給して、さらに、吸水性樹脂粉末（１８）に１，４−ブタンジオール／プロピレングリコール／水／イソプロパノール＝０．３２／０．５０／２．７３／０．５１（重量％／対粉末）からなる表面架橋剤水溶液をスプレー径約２５０μｍで噴霧した。次いで、得られた混合物を１９５℃で４０分の連続再加熱処理を行うことで、表面架橋された吸水性樹脂粉末（１９）を得た。結果を表２に示す。なお、連続混合時の高速連続混合機（タービュライザー）の内壁温度は、粉温と摩擦熱で約７０〜８０℃であり、加熱されているため付着はほとんどなかった。
【００９４】
（実施例２０）…水性液添加と後加熱／粉温５０℃
実施例１９において、表面架橋剤水溶液を、エチレングリコールジグリシジルエーテル／プロピレングリコール／水／イソプロパノール＝０．０３／１／３／０．９（重量％／対粉末）からなる表面架橋剤水溶液に変更して、吸水性樹脂粉末（１８）に噴霧し、さらに、１９０℃で３５分の連続再加熱処理を行うことで、表面架橋された吸水性樹脂粉末（２０）を得た。結果を表２に示す。
（実施例２１）…水性液添加と後加熱／粉温３０℃
実施例１８で得られた吸水性樹脂粉末（１８）を粉温３０℃までさらに冷却した以外は、実施例１９と同様に表面架橋剤水溶液を混合し、さらに、１９５℃で４０分の連続再加熱処理を行った。粉温３０℃まで冷却することで、長時間運転すると連続混合・輸送時に若干の凝集が見られ、また、反応時間が若干延びた。結果を表２に示す。
【００９５】
（比較例４）…水性液添加と後加熱／ただし強制冷却なし
実施例１４において、強制冷却することなく、乾燥重合体（４）を乾燥機から取り出して即座に粉砕することで比較吸水性樹脂粉末（３）を得た。次いで、実施例１５において、吸水性樹脂粉末（１４）に代えて、８５０μｍ以下に粒度を調整した比較吸水性樹脂粉末（３）に対して同様に水性液を添加した。４０〜８０℃に強制冷却しない比較吸水性樹脂粉末（３）では、実施例１５と同じ粒度に調整しても、混合機中での凝集や付着が徐々に見られ、連続操業が困難であった。結果を表２に示す。
【００９６】
（比較例５）…乾燥重合体（５）の粉砕／ただし強制冷却なし
実施例１８において、乾燥重合体（５）を強制冷却することなく、そのまま実施例１８と同じロール粉砕機に供給した。連続粉砕をはじめて２時間後、凝集物由来の粉砕機の異常音や凝集物の付着が生じはじめた。粉砕によって得られた比較吸水性樹脂粉末（５）の粒度分布を表１に示す。
（比較例６）…水性液添加と後加熱／ただし強制冷却なし
実施例１９において、吸水性樹脂粉末（１９）に代えて、比較例５で得られた比較吸水性樹脂粉末（５）を用いる以外は、実施例１９と同様に行うことで、表面架橋された比較吸水性樹脂粉末（６）を得た。結果を表２に示す。
【００９７】
（実施例２２）…衛生材料の作成
実施例１９で得られた、表面架橋された吸水性樹脂粉末（１９）５０重量部と、粉砕木材パルプ５０重量部とを、ミキサーを用いて乾式混合した。次いで、得られた混合物を空気しょう造することにより、１２ｃｍ×３８ｃｍのウェッブに成形した。圧力２ｋｇ／ｃｍ2（約１９３ｋＰａ）でプレスすることで、坪量約５２６ｇ／ｍ2の吸収体（１）を得た。次いで、レッグギャザーを有するバッグシート（液不透過性シート）、液透過性トップシートの間に吸収体（１）を組み込むことで、重量４７ｇでコア濃度５０重量％の紙おむつ（１）を作成した。
【００９８】
紙おむつ（１）に対して、２０ｇ／ｃｍ2（約１．９３ｋＰａ）の荷重を平面板状おもりで与え、板の中心の穴より加圧下で生理食塩水を注入したところ、冷却工程を経て得られた吸水性樹脂粉末（１９）より得られた紙おむつ（１）は、約４７０ｇの飽和吸収能を示した。
（比較例７）…衛生材料の作成
実施例２２において、吸水性樹脂粉末（１９）に代えて比較例６で得られた比較吸水性樹脂粉末（６）を用いる以外は、実施例２２と同様に行うことにより、比較紙おむつ（１）を得た。比較紙おむつ（１）は実施例２２と同様に、２０ｇ／ｃｍ2（約１．９３ｋＰａ）の荷重を平面板状おもりで与え、板の中心の穴より加圧下で生理食塩水を注入したところ、約４１０ｇの飽和吸収能を示し、比較紙おむつ（１）は、冷却工程を経た吸水性樹脂粉末（１９）より得られた紙オムツ（１）よりも劣っていた。
【００９９】
【表１】

Figure 0004676625
【０１００】
【表２】
Figure 0004676625
【０１０１】
表１に示した実施例１〜７および実施例１４は、粉砕後の吸水性樹脂粉末の平均粒子径が２００μｍ〜６００μｍの範囲であり、さらに１５０μｍ以下ないし８５０μｍ以上の粒子の割合が１５重量％以下という、本発明において好ましい範囲となっていることが分かる。一方、比較例１〜２では、粉砕後の吸水性樹脂粉末の平均粒子径が２００μｍ〜６００μｍの範囲から外れており、さらに１５０μｍ以下ないし８５０μｍ以上の粒子の割合が１５重量％を超えていることが分かる。
また、表１に記載の結果から、加熱乾燥後に乾燥重合体を強制冷却、好ましくは８５℃〜３５℃、より好ましくは８０〜４０℃、さらに好ましくは７０〜４５℃の範囲に強制冷却する本願実施例１〜５では、強制冷却しない本願比較例１，２に比べて、所定粒度から外れたオン品（８５０μｍ以上）が非常に減少しており、本発明では平均粒径や粒度分布に優れていることが分かる。
【０１０２】
また、表１に記載の結果より、本発明では、乾燥重合体の金網への附着や目詰まりも減少して、乾燥効率（乾燥速度、均一性）が上昇する事が分かる。また、４０℃と６０℃とでは大きな効果の差もなく、冷却設備の大きさを考えると６０℃までで十分でもあることも分かる。さらに、表には記載しないが、本発明の吸水性樹脂粉末は、粉砕後の凝集も少ないという利点も示す。
表２に記載の結果より、本発明では水性液の添加も均一で、物性に優れていることが判る。また、実施例１０〜１３の比較で粉砕後の嵩比重は０．６５ｇ／ｍｌ以上の場合、より加圧下吸水倍率（特に４．９０ｋPa）も向上することがわかる。なお、表の（ ）に示すように、衝撃後にも加圧下吸収倍率（１．９３ｋＰａおよび４．９０ｋPa ）はほとんど低下せず、耐衝撃性や通液性も優れている。実施例１５〜１７の比較で、粉体の温度や混合機内壁の温度が水性液の添加に重要であることが判る。
【０１０３】
さらに上記実施例は一連の連続操作で比較したものであるが、本発明の効果は連続的に生産する場合、特に１ラインあたり吸水性樹脂粉末で１ｔ／日以上、好ましくは１０ｔ／日以上の連続乾燥、連続粉砕およびその後の水性液添加する場合、より顕著に現れる。
なお、発明の詳細な説明の項においてなした具体的な実施態様、または実施例は、あくまでも本発明の技術内容を明らかにするものであって、そのような具体例にのみ限定して狭義に解釈されるべきものではなく、本発明の精神と次に記載する特許請求事項の範囲内で、いろいろと変更して実施することができるものである。
【図面の簡単な説明】
【図１】 本発明の吸水性樹脂粉末の製造工程の代表例を表す工程図。本発明は、重合、乾燥、粉砕を含む連続プロセスに適しており、その一例を示す。[0001]
BACKGROUND OF THE INVENTION
  The present invention is a water absorbent resin powder.EndIt relates to a manufacturing method. More specifically, it is a method for producing a water-absorbent resin powder excellent in particle size distribution and physical properties, and prevents the adhesion and aggregation in the production process, and further provides a production method excellent in energy efficiency, drying efficiency, and productivity. To do.
  Furthermore, in the method of obtaining a modified water-absorbing resin powder by adding an aqueous liquid to the obtained powder, the uniform mixing of the aqueous liquid is further improved without using a special mixer or organic solvent. And a method for further improving the physical properties of the water-absorbent resin powder.
[0002]
[Prior art]
In recent years, for the purpose of absorbing a large amount of water, water-absorbing resins have been widely used as one of the materials constituting sanitary materials such as paper diapers, sanitary napkins, and incontinence pads. In addition to sanitary materials, water-absorbing resins are widely used for the purpose of water absorption and water retention, such as soil water retention agents and drip sheets for foods.
Examples of the water-absorbing resin include a crosslinked polyacrylic acid partial neutralized product, a hydrolyzate of starch-acrylonitrile copolymer, a neutralized product of starch-acrylic acid graft polymer, and a vinyl acetate-acrylic acid ester copolymer. Polymer saponified product, acrylonitrile copolymer or acrylamide copolymer hydrolyzate or cross-linked product thereof, cross-linked product of carboxymethylcellulose, copolymer cross-linked product of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), polyethylene Oxide crosslinked bodies, polyallylamine crosslinked bodies, polyethyleneimine crosslinked bodies, and the like are known, and many of these are used in powder form.
[0003]
As a method for producing these water-absorbent resins, there is a method in which a water-containing gel-like cross-linked polymer obtained by polymerizing an aqueous solution of a monomer containing a cross-linking agent is dried and further pulverized as necessary to obtain a powder. Although it is the mainstream, the water-containing gel-like crosslinked polymer of water-absorbing resin is very difficult to grind after drying and drying due to its high water absorption ability, adhesiveness and adhesion, and low heat resistance, and productivity The physical properties and energy efficiency of the resulting water-absorbent resin were very poor.
As a method for drying the water-containing gel-like crosslinked polymer of the water-absorbent resin, for example, drum dryer drying (Japanese Patent Laid-Open No. 54-53165), a dry powdered acrylic polymer and a water-containing gel are mixed and stirred and dried. (Japanese Unexamined Patent Publication No. 57-117551), azeotropic dehydration (Japanese Unexamined Patent Publication No. 57-198714), drying at a specific dew point (Japanese Unexamined Patent Publication No. 1-26604 / US Pat. No. 4,920,202), freeze drying (Japanese Unexamined Patent Publication No. -304127, JP-A-1-304128), a method of stirring and drying in a cylindrical drier (JP-A-2-240112 / US Pat. No. 5,00577171), a method of drying after extruding a gel through specific holes (US patent) No. 5,275,773), microwave drying (Japanese Patent Laid-Open No. 5-209010 / US Pat. No. 5,075,344), a method of drying with hot air after using a specific gel shredder (special feature) No. 5-230124), a method of drying with hot air while measuring the differential pressure (JP-A-8-73518), a method of adding a surfactant and stirring and drying (JP-A-8-134134), after standing and drying A method of pulverizing and then stirring or fluid drying (Japanese Patent Laid-Open No. 11-240914 / European Patent 0926162) is known.
[0004]
In addition, a drying method is known in which a water-containing gel-like crosslinked polymer is laminated on a punching metal or wire mesh for drying, but the dried polymer after drying has poor releasability and adheres to the wire mesh or pores. Due to the clogging, there is a problem that the drying efficiency is greatly reduced due to a decrease in air permeability, particularly in hot air drying. In order to prevent such adhesion and clogging, a drying method using a special conveyor having pins (Japanese Patent Laid-Open No. 7-270070 / German Patent 1951769) is also known.
Further, in addition to the physical properties (water absorption magnification, water-soluble content, liquid permeability, etc.), the particle size distribution of the water-absorbing resin is important, and a water-absorbing resin having a specific narrow particle size (Japanese Patent Laid-Open No. 1-132802 / US Patent) No. 5061259, JP-A-2-196802 / US Pat. No. 5,244,735, JP-A-2-191604 / US Pat. No. 4,973,632, JP-A-6-507564 / US Pat. No. 5,419,956, European Patent 0629411) In addition, a plurality of water-absorbent resins having a particle size distribution (European Patent No. 0845272, Japanese Patent Laid-Open No. 11-130978) are also known.
[0005]
Therefore, efficient classification is required as a classification method for adjusting the particle size of interest, and as a classification method of the water-absorbent resin after drying, a method using a heated or insulated sieve (Japanese Patent Laid-Open No. 10-202187). / European Patent No. 0855232) and a method using a classification network coated with Teflon (Japanese Patent Laid-Open No. 11-156299) is also known. There is also known a method for classifying an undried product at the time of drying before or during the pulverization process (Japanese Patent Laid-Open No. 11-292919 / European Patent No. 0948997).
However, even in these methods, the water-absorbent resin and its water-containing gel-like cross-linked polymer are very difficult to crush after drying and drying because of their high water absorption ability, adhesiveness, and low heat resistance. The physical properties and particle size distribution of the resulting water-absorbent resin were reduced, and the energy efficiency and productivity were very poor. In addition, after the pulverization and classification, powder agglomeration was observed in the production process, which had the problem of reducing production efficiency and quality.
[0006]
Furthermore, a method for improving the particle size distribution of the water-absorbent resin powder and the absorption characteristics under pressure by adding water alone or an aqueous liquid containing an additive to the obtained polymer powder is known. It is frequently used for granulation (US Pat. No. 5,369,148), surface cross-linking (US Pat. Nos. 5,409,771, 5,422,405, and 5,597,873) and reduction of residual epoxy compounds (US Pat. No. 5,981,070).
However, since the water-absorbent resin instantly absorbs water and exhibits tackiness, conventionally, not only is the improvement in physical properties unsatisfactory due to the non-uniform mixing of the aqueous liquid, and in some cases, it is not satisfactory. Aggregates of water-absorbing resin produced by uniform mixing adhered to the mixer, making continuous operation itself difficult. In addition, polyhydric alcohol is preferable as a cross-linking agent and its solvent from the viewpoint of physical properties and safety, but due to its high hydrophilicity and viscosity, uniform mixing of polyhydric alcohol aqueous solution into water absorbent resin among these aqueous liquids. Was particularly difficult.
[0007]
Therefore, when an aqueous liquid is added to the water-absorbent resin powder for modification, use of a special mixer (European Patent 0450923, European Patent 081873, etc.), use of inorganic powder (US Pat. No. 4,587,308), aqueous Although a technique for using an organic solvent in a liquid (US Pat. No. 4,734,478) is known, the use of an organic solvent, particularly the use of a volatile organic solvent, causes a decrease in physical properties in addition to cost, environmental problems and safety. It was accompanied by a problem. Further, a technique (WO 98/49221) for controlling the physical properties (AUL / Absorbency under Load) of a resin to a specific range when adding an aqueous liquid to the water-absorbing resin is also known, but this method is not applicable. Also, the water-absorbent resin powder is very limited and its production is difficult.
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned conventional problems, and the purpose thereof is to efficiently dry or pulverize the hydrated gel-like crosslinked polymer without thermal deterioration and adjust the particle size for the above-mentioned present situation. By providing a manufacturing method that can produce a water-absorbent resin powder having a narrow particle size distribution and high physical properties, and that prevents adhesion and agglomeration in the manufacturing process, and further exhibits energy efficiency and high productivity. is there.
Furthermore, in the method of adding an aqueous liquid, the mixing property is further improved, and water is absorbed by adding a uniform aqueous liquid (especially an aqueous solution of a crosslinking agent or an aqueous solution of a polyhydric alcohol) without using a special mixer or an organic solvent. It is to further improve the physical properties of the conductive resin powder.
[0009]
[Means for Solving the Problems]
  As a result of intensive studies to achieve the above object, the present inventors have made a method for producing a water-absorbent resin powder that is obtained by heating and drying a hydrogel crosslinked polymer obtained by polymerizing an aqueous monomer solution containing a crosslinking agent. Of the water-absorbent resin powder after pulverizationweightThe average particle diameter is in the range of 200 to 600 μm, and further particles of 150 μm or less to 850 μm or more.totalThe ratio is 15% by weight or less, and the dried polymer after heat drying is before or during pulverization.ForcedThe manufacturing method characterized by cooling has high energy efficiency, no aggregation of powder in the manufacturing process, very little heat deterioration and adhesion during drying, and extremely efficient grinding after drying. The present invention has been completed.
[0010]
  Furthermore, water absorbent resin powderForcedWe found that by cooling and further adjusting the bulk specific gravity, it was possible to improve the mixability of aqueous liquids (especially aqueous solutions of cross-linking agents and polyhydric alcohols), which had been difficult in the past, and to improve continuous operability and physical properties. did.
  That is, the method for producing a water-absorbent resin powder according to the present invention includes:
  A method for producing a water-absorbent resin powder, wherein a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent is heated and dried and then pulverized.
  Of the water-absorbent resin powder after the grindingweightThe average particle diameter is in the range of 200 to 600 μm, and further particles of 150 μm or less to 850 μm or more.totalThe proportion is 15% by weight or less,
  Before or during pulverization of dried polymer after heat dryingForcedCooling,
It is characterized by that.
[0011]
  In addition, another water absorbent resin powder production method according to the present invention,
  A method for producing a water-absorbent resin powder, wherein a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent is heated and dried and then pulverized.
  The heat obtained by forcibly cooling the dried polymer after heat drying is reused for forced heating in the water-absorbent resin production process.,
It is characterized by that.
  In addition, another water absorbent resin powder production method according to the present invention,
  This is a method for producing a water-absorbent resin powder in which an aqueous liquid is added in a mixer to a powder obtained by heating and drying a hydrogel crosslinked polymer obtained by polymerizing an aqueous monomer solution containing a crosslinking agent. And
  The heating and drying temperature is in the range of 110 to 230 ° C., and the dry polymer is brought to 80 to 35 ° C. before adding the aqueous liquid.ForcedCooling and bulk specific gravity of the dried polymer after grinding(Measured according to JIS K 3362)Is 0.65 g / ml or more,
It is characterized by that.
[0012]
  In addition, another water absorbent resin powder production method according to the present invention,
  This is a method for producing a water-absorbent resin powder in which an aqueous liquid is added in a mixer to a powder obtained by heating and drying a hydrogel crosslinked polymer obtained by polymerizing an aqueous monomer solution containing a crosslinking agent. And
  The heating and drying temperature is in the range of 110 to 230 ° C., and the dry polymer is brought to 80 to 35 ° C. before adding the aqueous liquid.ForcedCooling and stirring mixer with inner wall temperature of the mixer of 40 ° C. or higher, and reheating to 110 to 230 ° C.,
It is characterized by.
[0013]
  In addition, another water absorbent resin powder production method according to the present invention,
  A method for producing a water-absorbent resin powder, wherein a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent is heated and dried and then pulverized.
  Forcibly cooling the dried polymer after heat drying;
  Crushing the dried polymer(Measured according to JIS K 3362)A water absorbent resin powder of 0.65 g / ml or more,
  Further surface cross-linking the cooled water-absorbent resin powder,
It is characterized by.
[0014]
  In addition, another water absorbent resin powder production method according to the present invention,
  A method for producing a water-absorbent resin powder, wherein a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent is heated and dried and then pulverized.
  Forcibly cooling the dried polymer after heat drying;
  Crushing the dried polymer(Measured according to JIS K 3362)A water absorbent resin powder of 0.65 g / ml or more,
  Adding an aqueous liquid to the cooled water-absorbent resin powder;
  The aqueous liquid is added in a stirred mixer with the inner wall heated,
It is characterized by.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, an embodiment of the present invention will be described in detail.
  The method for producing a water-absorbent resin powder of the present invention is a method for producing a water-absorbent resin powder in which a hydrogel crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent is heated and dried and then pulverized. Of the water-absorbent resin powder after grindingweightThe average particle diameter is in the range of 200 to 600 μm, and further particles of 150 μm or less to 850 μm or more.totalThe ratio is 15% by weight or less, and the dried polymer after heat drying is before or during pulverization.ForcedIt is a manufacturing method characterized by cooling.
[0017]
First, the method for producing the hydrogel crosslinked polymer of the present invention will be described below.
In the present invention, the water-absorbing resin means 3 to 1000 times, preferably 5 to 1000 times, more preferably 10 to 800 times, and still more preferably 100 to 700 times as much as its own weight under no load at the time of saturation swelling. It is a crosslinked polymer that can be absorbed to form a water-insoluble swelling hydrous gel. The water-insoluble in the present invention usually means that the amount of water-soluble component in the water-absorbent resin is 40% by weight or less, preferably 20% by weight or less, more preferably 15% by weight or less, particularly preferably 10% by weight or less. Most preferably, it is 5% by weight or less. In addition, the measuring method of these physical properties is demonstrated in the column of the below-mentioned Example. If the amount of the water-soluble component is large, not only the physical properties (absorption under pressure, liquid flow rate under pressure, etc.) are lowered, but it is difficult to uniformly add the aqueous liquid of the water-absorbent resin powder.
[0018]
The hydrogel crosslinked polymer used in the method for producing a water-absorbent resin powder according to the present invention is a polymer obtained by polymerizing an aqueous monomer solution containing a crosslinking agent. Examples of the water-containing gel-like crosslinked polymer include one or a mixture of water-absorbing cationic, anionic and nonionic crosslinked polymers, but are preferably essential from the viewpoint of most exerting the effects of the present invention. It is preferable that the main component is an anionic crosslinked polymer, and more preferably, the main component of the functional group is a carboxyl group.
In the present invention, the anionic cross-linked polymer is preferably a hydrogel cross-linked polymer using acrylic acid (salt) as the acid group-containing unsaturated monomer (salt) because of its effect. It is more preferable that it is a hydrogel crosslinked polymer obtained by polymerizing acrylic acid (salt) neutralized by 90 mol%, further 0-80 mol%, and in particular, 0-10 mol% is neutralized. More preferably, it is a hydrogel crosslinked polymer obtained by polymerizing acrylic acid (salt). That is, conventionally, the polyacrylic acid crosslinked body, particularly the unneutralized or low-neutralized polyacrylic acid crosslinked body, has had a large decrease in physical properties in the drying step and the pulverizing step, and therefore the method of the present invention is suitably applied.
[0019]
The monomer is mainly composed of the acrylic acid (salt), and if necessary, can be copolymerized with other monomers other than the acrylic acid (salt), that is, the acrylic acid (salt). Other monomers may be included, and the water-absorbing resin may be obtained with a monomer other than acrylic acid.
The monomer other than acrylic acid to be used is not particularly limited, and specifically, for example, methacrylic acid, maleic acid, crotonic acid, sorbic acid, itaconic acid, cinnamic acid, maleic anhydride , Vinylsulfonic acid, allylsulfonic acid, vinyltoluenesulfonic acid, styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfone Acid, acid group-containing unsaturated monomers such as 2-hydroxyethyl (meth) acryloyl phosphate and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2- Hydroxyethyl (meth) acrylate, 2-hydroxypro Nonionic hydrophilic group-containing unsaturated single molecules such as ru (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine Examples include a polymer. Only one kind of these other monomers may be used, or two or more kinds may be appropriately mixed and used. When these other unsaturated monomers are used, the proportion of the other unsaturated monomers in the monomer containing acrylic acid is set to 50 mol% or less, preferably 30 mol% or less. Good.
[0020]
When an acid group-containing monomer or a base-containing monomer is used in the present invention, the acid group functional group or base functional group of the monomer or polymer may be neutralized. The neutralizing agent used in the present invention is not particularly limited, and a known inorganic or organic base or acid can be used for the monomer or polymer.
For example, when an acid group-containing monomer is used in the present invention, specific examples of the monomer or polymer neutralizer base include sodium hydroxide, potassium hydroxide, lithium hydroxide, and carbonate. Inorganic bases such as lithium, ammonium hydroxide, sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, ethanolamine, diethanolamine, triethanolamine, polyethyleneimine, polyallylamine, (poly) lysine And organic bases such as (poly) arginine. In addition, when a base-containing monomer is used in the present invention, similarly, an inorganic acid or an organic acid is appropriately selected as a neutralizing agent.
[0021]
When a polymer neutralizer (for example, polyamine) is used, a crosslinked product may be used. Among these neutralizers, alkali metal salts, particularly lithium salts or sodium salts are preferably used. 50 to 90 mol%, further 60 to 80 mol% of the groups are neutralized. The final neutralization rate of the water absorbent resin obtained in the present invention is preferably in the above range.
Neutralization may be performed as the above base or acid as an aqueous solution, dispersion or gel, or by so-called dry blend (powder mixing) in which the base or acid is added as a solid. Further, the neutralization may be a monomer, may be performed with a hydrogel crosslinked polymer before drying, may be performed with respect to a dried polymer after drying, or a pulverized product or a classified product thereof, Neutralization may be used in combination. Further, the neutralization may be performed by completely reacting the acid group and the base, or by reacting only a part by a method such as dry blending to obtain a water absorbent resin composition that is a mixture of the acid group and the base. It may be neutralized by obtaining.
[0022]
Further, in the case of neutralization in the present invention, as a technique thereof, post-neutralization of a water-containing gel-like crosslinked polymer or a dry polymer thereof, particularly post-neutralization of a dry polymer is one of the preferred techniques of the present invention. . In other words, in the present invention, an unneutralized or low-neutralized polyacrylic acid crosslinked product can be efficiently dried (powdered) without deterioration of its physical properties, so that it can be neutralized after using the polyacrylic acid crosslinked product powder. Therefore, it is preferable that a water-absorbing resin having higher physical properties can be obtained by a method of post-neutralizing the crosslinked polyacrylic acid powder.
Further, when obtaining the above water-containing gel-like crosslinked polymer, the means may be radical crosslinking or self-crosslinking as long as the polymer becomes water-insoluble. Introduce inside. The internal cross-linking agent may be a compound having a plurality of polymerizable unsaturated groups and / or reactive groups in one molecule, and a plurality of substituents copolymerizing and / or reacting with the monomer in one molecule. What is necessary is just a compound which has. When using a compound having a plurality of reactive substituents in one molecule, a crosslinking agent may be uniformly added to the water-soluble or water-insoluble polymer gel after polymerization, and the inside thereof may be post-crosslinked.
[0023]
Specific examples of the internal crosslinking agent include N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, and 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, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethyl Glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerol, pentaerythritol, ethylenediamine, polyethyleneimine, and glycidyl (meth) acrylate and the like, but is not particularly limited.
[0024]
These internal crosslinking agents may be used alone or in combination of two or more. Of the above-exemplified internal cross-linking agents, it is preferable to use an internal cross-linking agent having a plurality of polymerizable unsaturated groups in one molecule at the time of polymerization because the physical properties of the resulting water-absorbent resin can be further improved.
The amount of the internal cross-linking agent used is preferably 0.005 to 3 mol%, more preferably 0.01 to 1. mol. It is used in a range of 5 mol%, more preferably 0.05 to 1 mol%. When the amount of the internal cross-linking agent used is less than 0.005 mol% and more than 3 mol%, a water absorbent resin having desired physical properties may not be obtained.
[0025]
In the polymerization, the reaction system includes starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), polyacrylic acid (salt) cross-linked hydrophilic polymers (and the like) The addition amount of the product is preferably 0 to 40 parts by weight, more preferably 0 to 10 parts by weight based on 100 parts by weight of the monomer); chain transfer agents such as hypophosphorous acid (salt), chelating agents, You may add foaming agents, such as carbonate (The addition amount about the above thing is 0-5 weight part with respect to 100 weight part of monomers, and 0-1 weight part is more preferable).
The polymerization method of the monomer is not particularly limited, and for example, a known method such as aqueous solution polymerization, reverse phase suspension polymerization, bulk polymerization, precipitation polymerization or the like can be employed. Among these, from the viewpoint of ease of control of the polymerization reaction and the performance of the resulting water-absorbent resin, in the present invention, a method of polymerizing the monomer component in an aqueous solution, that is, aqueous solution polymerization and reverse phase suspension polymerization. preferable.
[0026]
The reverse phase suspension polymerization is a polymerization method in which an aqueous monomer solution is suspended in a hydrophobic organic solvent. For example, U.S. Pat. Nos. 4,093,764, 4,367,323, 4,446,261, 4,683,274, and 5,244,735. Are described in US patents. Aqueous polymerization is a method in which an aqueous monomer solution is polymerized without using a dispersion solvent. For example, US Pat. No. 5,264,495, US Pat. No. 5,145,906 and US Pat. No. 5,380,808, and European patents such as European Patents 081636, 09555086, and 0922717. In the present invention, including these, the polymerization method is not particularly limited, but the present invention is particularly preferably used for aqueous solution polymerization which has been difficult to dry and pulverize conventionally.
[0027]
The concentration of the monomer component when employing aqueous solution polymerization and reverse phase suspension polymerization as the polymerization method, that is, the ratio of the monomer in the aqueous solution is not particularly limited, but is preferably from the viewpoint of physical properties. It is 10 to 70% by weight, more preferably 15 to 60% by weight, still more preferably 20 to 50% by weight, and particularly preferably 30 to 45% by weight.
The reaction conditions such as reaction temperature and reaction time may be appropriately set according to the monomer used, and are not particularly limited, but are usually 0 ° C. to boiling point, preferably 10 to 110 ° C., More preferably, the polymerization is performed within a range of 15 to 100 ° C. (minimum to maximum temperature, or start temperature to peak temperature), and such polymerization is preferably performed in an atmosphere of an inert gas such as nitrogen. Furthermore, the atmosphere during the polymerization may be reduced or increased, but is usually carried out at normal pressure.
[0028]
For polymerization initiation, for example, radical polymerization initiators such as potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) dihydrochloride, etc. Alternatively, an ultraviolet ray or an active energy ray such as an electron beam using an ultraviolet polymerization initiator as necessary can be used, and these may be used in combination.
Moreover, when using this oxidizing radical polymerization initiator, you may perform redox polymerization using reducing agents, such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, L-ascorbic acid, together, for example. The amount of these polymerization initiators used is preferably in the range of 0.001 to 2 mol%, more preferably in the range of 0.01 to 0.5 mol%. The polymerization initiator is usually added after being dissolved or dispersed in a solvent such as water.
[0029]
The hydrogel cross-linked crosslinked polymer obtained by the above polymerization is fragmented as necessary and then dried. In the present invention, drying is preferably carried out as a particulate hydrogel crosslinked polymer (for example, an average particle size of 2 cm or less, preferably 1 cm or less, more preferably 5 mm or less) from the viewpoint of physical properties. As a fragmentation method for making the hydrogel crosslinked polymer into particles in the present invention, fragmentation may be performed simultaneously with polymerization using a kneader or the like, or may be separately fragmented after polymerization. The fragmentation during polymerization and the fragmentation after polymerization may be used in combination. In addition, when a hydrogel polymer is a particulate form and is not dried, for example, in a film form etc., a physical property and a particle size may be inferior.
[0030]
The particle size of the hydrogel crosslinked polymer prior to drying is preferably a weight average particle size from the viewpoint of drying efficiency and physical properties, preferably 45 to 4000 μm, more preferably 50 to 2000 μm, more preferably 100 to 1500 μm, More preferably, it is the range of 200-1000 micrometers. As an apparatus suitable for such subdivision, for example, a kneader, a vertical slitting slitter equipped with a cutter blade, a transverse slitting slitter equipped with a cutter blade, a cutter-type crusher equipped with a rotary blade, a predetermined pore diameter An example is meat chopper. In addition, when the weight average particle diameter of the hydrogel crosslinked polymer is out of the above range, there is a risk of causing a decrease in water absorption rate or an increase in water-soluble content of the resulting water-absorbent resin powder.
[0031]
The water-containing gel-like crosslinked polymer thus obtained is essentially heat-dried. In the present invention, the term “drying” means that the solid content of the hydrated gel-like crosslinked polymer is 80% by weight or more, preferably 85% by weight or more, more preferably 90% by weight or more, and particularly preferably 93% by weight or more. Indicates a state.
Further, such drying in the present invention does not necessarily require a dry polymer having a solid content of 100% by weight (zero water content), preferably 99% by weight or less, more preferably 98% by weight or less, and even more preferably 98% by weight or less. The hydrogel crosslinked polymer is preferably dried to 97 wt% or less, most preferably 97 to 93 wt%.
[0032]
That is, if the solid content after drying is high, the physical properties due to surface crosslinking are also easily improved, and the powder is less agglomerated in the subsequent manufacturing process and easy to handle with the powder, but only takes time to dry. In addition, there is a case where physical properties are deteriorated due to an increase in fine powder during pulverization, subsequent processes and use, and drying for a long time. However, in the present invention in which forced cooling is performed after drying, the solid content of the dried polymer or water-absorbent resin powder is excessively reduced as in the past in order to prevent the powder from agglomerating in the manufacturing process and to crush the dried polymer. Since it is not necessary to raise, drying time can be shortened and physical properties can be improved.
The heat drying method used in the present invention is not particularly limited, and for example, one of drying methods such as hot air drying, thin film drying using a drum dryer, reduced pressure drying method, stirring drying, fluidized bed drying or the like. Two or more kinds can be used, and the continuous or batch of drying is not particularly limited. Among these, from the viewpoint of physical properties and drying efficiency, hot air drying, particularly continuous hot air drying is preferably used in the present invention. For example, it may be allowed to stand and dry on a belt.
[0033]
For such hot-air drying, from the viewpoint of drying efficiency, a particulate water-containing gel-like crosslinked polymer is laminated on a punching metal having a wire mesh / or holes or slits, and then the vertical or horizontal direction of the gel, preferably in the vertical direction, Hot air may be ventilated between the voids of the stacked particles. For example, in the case of a hole or wire mesh, the wire mesh or hole diameter to be used may have a ventilation hole of about 0.1 to 5 mm, and further about 0.2 to 2 mm. In addition, the lamination of the gel on the metal mesh or punching metal is preferably performed in the form of a particulate hydrogel cross-linked layer having a constant thickness of 1 to 20 cm, preferably 1.5 to 10 cm, more preferably 2 to 8 cm in view of physical properties after drying. The coalescence may be laminated.
[0034]
The drying temperature for drying the above hydrogel crosslinked polymer is usually 100 ° C. or higher, more preferably 110 to 230 ° C., preferably 130 to 200 ° C., particularly preferably 150 to 200 ° C. in view of physical properties and productivity. What is necessary is just to set to the grade of 190 degreeC. The drying temperature is defined by the material temperature or the temperature of the heat medium (hot air or the like), but is preferably defined by the heat medium temperature. Further, the drying temperature may be constant during the drying period, or may be appropriately changed during the drying within the above temperature range. Furthermore, when performing hot air drying, the dew point of the hot air is preferably in the range of 40 to 100 ° C., more preferably 50 to 90 ° C., and still more preferably 60 to 85 ° C., from the physical properties and energy efficiency.
[0035]
The dry polymer obtained in this way is essentially forcedly cooled and then ground or simultaneously. In the present invention, forced cooling and pulverization may be performed at the same time, but preferably pulverized after forced cooling. The forced cooling referred to in the present invention is an external and intentional cooling operation or cooling step of the dried polymer, and the pulverization is the flowability of the obtained dried polymer or its aggregate (block-like product). It is a mechanical operation to make a powder. Furthermore, crushing does not lead to physical destruction of the dried polymer or reduction in particle size, but it is a mechanical operation to lightly agglomerate from several mm to several tens of mm. is there.
It should also be noted that the particulate hydrogel crosslinked polymer that has been laminated and dried tends to become a block-like dried product that loses fluidity due to aggregation between particles after drying. Since such a block-like material is an aggregate of dry polymer particles, it has continuous voids and air permeability to the inside of the block, but has no fluidity due to aggregation, so a pulverization (pulverization) step Need.
[0036]
As a method for forced cooling in the present invention, the drying polymer may be cooled to a predetermined temperature by intentionally providing a cooling step between the drying step and the pulverization step. (1) A method of forcibly cooling the unit by placing it in a container (hopper) or a cylinder that has a cooling heat transfer surface and if necessary, and forcibly cooling, (2) It is allowed to cool sufficiently on a continuous belt (used for drying) (3) A method of forced cooling by passing cold air through a polymer, (4) A method of forced cooling simultaneously with transportation using cold air, (5) A low-temperature screw conveyor having a cooling heat transfer surface, etc. Can be mentioned.
Among these methods, from the viewpoint of cooling efficiency and the fluidity of the dry polymer, the method of (3) cooling air is preferably used in the present invention. In that case, only the surface of the dry polymer may be vented. However, it is preferable that the laminated dry polymer or its block-like product is ventilated in the vertical direction or the horizontal direction, preferably in the vertical direction, so that more effective forced cooling can be performed by ventilating the gaps between the stacked particles. In addition, when laminating | stacking, the above-mentioned range is preferable for the thickness.
[0037]
In the present invention, forced cooling is essential before pulverization or during pulverization, and is small-scale polymerization, drying, and pulverization in a laboratory. Unlike laboratory-scale drying and pulverization, which is naturally free to cool because it is free for several hours or more, the purpose of the present invention is not achieved when production scale drying does not perform forced cooling before or during pulverization. I understood that. That is, the present invention can be applied to continuous drying, continuous pulverization, and subsequent continuous aqueous liquid addition at a large scale (for example, 1 t / day or more, preferably 10 t / day or more per line) in a production facility. Is more preferable.
[0038]
If forced cooling after heat drying, which is a feature of the present invention, is not performed, the pulverization or classification efficiency is greatly reduced, and a water-absorbent resin powder excellent in particle size distribution cannot be obtained with high productivity. Furthermore, when hot-air drying is performed on a wire mesh or punching metal, conventionally, the dry polymer adheres to the wire mesh or punching metal and causes clogging, which significantly reduces air permeability, drying efficiency, and productivity. In the present invention, there is no such problem, and there is no need for a special adhesion prevention device (Japanese Patent Laid-Open No. 7-270070) or attachment of a dryer or periodic removal of clogging. Moreover, by forced cooling before pulverization or during pulverization, the resulting water-absorbent resin powder has excellent particle size distribution and pulverization speed, and also greatly reduces the adhesion of powder in the pulverizer and the manufacturing process. . Further, it is not necessary to dry the water-absorbent resin powder excessively in order to prevent the powder from agglomerating in the subsequent manufacturing process, so that shortening of the drying time and improvement of physical properties are also achieved.
[0039]
The cold air (gas) used in the method (3) in the present invention is appropriately determined depending on the temperature of the target dry polymer, but is 60 ° C. or less, preferably 50 to −50 ° C., more preferably 40 to −− from the cooling efficiency. Forced cooling is performed with a gas of 10 ° C., particularly preferably 35 to 5 ° C., and the dew point of the gas is preferably 60 ° C. or less, more preferably 50 ° C. or less. The gas may be an inert gas such as nitrogen, or a mixed gas of an inert gas and air, but preferably air, particularly air that has passed through a filter.
Further, the wind speed is 10 to 0.1 m / sec, further about 5 to 0.5 m / sec, and the cooling time is preferably 60 to 0.1 min, more preferably 20 to 0.2 min. More preferably, it is the range for 10 to 0.5 minutes.
[0040]
As the forced cooling temperature in the present invention, the temperature of the dry polymer is 95 ° C. or less, preferably 85 to 35 ° C., more preferably 80 to 40 ° C., and further preferably 70 to 45 ° C. in achieving the present invention. It is forced to cool. The forced cooling temperature is obtained by appropriately measuring the material temperature with a contact-type thermometer or a non-contact-type thermometer (such as an infrared thermometer), and is controlled as necessary.
If the temperature of the dried polymer exceeds 95 ° C., the releasability from the wire mesh and punching metal of the dryer is difficult and the drying efficiency is low, and the efficiency of pulverizing and classifying the dried polymer is greatly reduced. In particular, it is difficult to obtain an excellent water absorbent resin powder having a narrow particle size distribution. If the cooling temperature is too low, not only a large time and equipment are required for cooling, but also surprisingly, aggregates of the water-absorbent resin powder are generated during pulverization and classification, which is not preferable. Furthermore, excessive cooling may be disadvantageous in terms of physical properties and energy for forced heating and surface cross-linking described later.
[0041]
Further, in achieving the present invention, the temperature drop of the dried polymer due to forced cooling is dependent on the heating drying temperature, but compared with the dried polymer before forced cooling, the temperature change of the polymer before and after cooling. Is preferably 40 ° C. or higher, more preferably 60 ° C. or higher, further preferably 80 ° C. or higher, and particularly preferably 100 ° C. or higher. What is necessary is just to forcibly cool to (for example, more preferably 80-40 degreeC).
Note that the heat removed from the dried polymer by forced cooling is preferably recycled. For example, as described above, in the present invention, the heat drying is hot air drying (particularly preferably, 150 to 180 ° C.), and the forced cooling is air cooling (particularly preferably the polymer is forced to be cooled in the range of 70 to 45 ° C.). However, when performing forced cooling by hot air drying and air cooling according to the present invention, the cold air used for forced cooling of the dried polymer is appropriately controlled by the air volume, air flow rate, polymer temperature, and the like. Is warm air or hot air (usually 50 ° C. or higher, preferably 50 to 200 ° C., more preferably 60 to 150 ° C., and still more preferably 70 to 110 ° C.). As such, it may be used as it is in the water-absorbing resin manufacturing process, or may be reheated and used in the water-absorbing resin manufacturing process such as hot air drying described above.
[0042]
The heat obtained by forced cooling in the present invention is preferably reused. As a manufacturing process to be reused, there is a heat retaining process, but the above-mentioned drying process is most preferable. That is, the cold air used for forced cooling in the present invention becomes warm air after aeration of the dried polymer. Therefore, in the present invention, hot air after forced cooling (for example, 60 to 150 ° C.) is preferably dried with hot air through a pipe. It is possible to perform continuous drying as a raw material of hot air supplied to the air supply port of the machine and used for drying. Thus, in the hot air drying of the present invention, hot air is produced using hot air generated by forced cooling instead of using room temperature air. It has the advantage of not discharging wind (waste gas) to the environment. Also from the viewpoint of recycling, forced cooling in which cold air is passed through the polymer is used for forced cooling of the present invention, and hot air drying is used for heat drying of the present invention.
[0043]
That is, the present invention is a method for producing a water-absorbent resin powder in which a water-containing gel-like cross-linked polymer obtained by polymerizing a monomer aqueous solution containing a cross-linking agent is heat-dried and then pulverized, and the dry polymer after heat-drying Also provided is a method for producing a water-absorbent resin powder, characterized in that the heat obtained by forcibly cooling the water is reused for forced heating in the production process of the water-absorbent resin. Here, reusing for forced heating means using the heat obtained in the forced cooling process in the forced heating process, and the forced cooling process and the forced heating process are included in the same production line. It may be a process that is included in a separate production line.
[0044]
In addition, when performing hot air drying and air cooling in the present invention, a fluidized bed or the like may be separately installed as a drying device and a cooling device. For example, when performing continuous hot air drying, a belt-type dryer is used. It is also preferable to use a part of the latter half of the dryer for the cooling step. In such a case, even if a cooling device is not separately provided, the ¼ to 1/20 portion of the hot air dryer belt, preferably the ½ to 1/16 portion of the second half of the belt, is separated separately, and cool air is sent as a cooling device. Thus, the forced cooling process may be performed, and further, the heat taken from the dried polymer may be recycled.
In the present invention, since the heat obtained by forced cooling of the dry polymer is reused, a process with excellent energy efficiency can be obtained. Also, by forcibly cooling the latter half of the dryer, the dried polymer can be peeled off from the belt mesh and punching metal.sexIs drastically improved, the belt is not clogged, and the drying efficiency is improved by improving the air permeability.
[0045]
  The dry polymer thus forcibly cooled to a predetermined temperature is then pulverized or classified, preferably essentially pulverized and further classified. The drying and pulverization or classification are preferably performed in a continuous process, and the time from the dryer outlet to the pulverizer inlet is within 10 minutes, preferably within 5 minutes, and more preferably within 2 minutes. In the present invention, even in such a continuous process, it is possible to dramatically improve the drying efficiency and the pulverization efficiency by inserting a forced cooling process between the drying process and the pulverization process.
  In the present invention, as the pulverization method, the dry polymer or its aggregate (block-like product) is flowable powder, preferablyweightThe powder is not particularly limited as long as it can be a powder having an average particle diameter of 2 mm or less. For example, a method of pulverization using a hammer-type pulverizer, a roll-type pulverizer, or a jet airflow-type pulverizer, One type or two or more types of crushing methods can be used. In addition, when the aggregation during drying is weak, the pulverization step may be performed by loosening the aggregation of the polymer by applying vibration to the dried polymer and classifying it without using a pulverizer.
[0046]
  In the present invention, after the above pulverization, if necessary / preferably classified, coarse particles and fine powder are removed. Of the water-absorbent resin powder thus obtained.weightThe average particle size is determined according to the purpose.For example, when the purpose is a sanitary material, the water absorbent resin powder finally obtained isweightThe average particle size is 200 to 600 μm, further 300 to 600 μm, more preferably 300 to 550 μm. Preferably, the total of particles of 150 μm or less to 850 μm or more is 15% by weight or less, more preferably 10% by weight or less. More preferably, it is 5 weight% or less.
  In particular, in the present invention, the water-absorbent resin powder obtained after pulverization and used in the next step is used.weightThe average particle diameter is in the above range, that is, in the range of 200 to 600 μm, and further, particles having a particle size of 150 μm or less to 850 μm or moretotalThe proportion is preferably 15% by weight or less.
[0047]
  The bulk specific gravity of the water-absorbent resin powder obtained in this way is the true specific gravity (g / cm determined uniquely by the monomer composition).3For example, when the water-absorbent resin is sodium polyacrylate, particularly a neutralization rate of 50 to 90 mol%, and further 60 to 80 mol%, the bulk specific gravity is usually 0.63 g / ml or more, Especially 0.65 g / mlmore than(Measured with an apparatus according to JIS K-3362). In the forced cooling method of the present invention, the water-absorbent resin powder after pulverization has less scale and is more rounded and has a uniform shape. Therefore, the bulk specific gravity tends to be high, and the bulk specific gravity is preferably 0.65 to 0. .89 g / ml, more preferably 0.67 to 0.88 g / ml, still more preferably 0.73 to 0.87 g / ml, still more preferably 0.74 to 0.86 g / ml, still more preferably 0.75 Adjusted to ˜0.85 g / ml.
[0048]
If the bulk specific gravity after pulverization is lower than 0.63 g / ml, even if the temperature is controlled, it becomes difficult to mix the aqueous liquid described later, and not only the physical properties decrease (absorption capacity under pressure, liquid permeability under pressure). Further, it is not preferable because the impact resistance (process damage) of the water-absorbent resin powder may be reduced, and the transportation cost may be increased due to the weight reduction per unit volume. On the other hand, if the bulk specific gravity is higher than 0.89 g / ml, it may be difficult to secure a liquid passing space between the gels during the liquid-permeable swelling under pressure.
After the pulverization, coarse particles (for example, 850 μm ON product) and fine powder (for example, 150 μm pass product) may be recycled as appropriate. Coarse particles are reground, and fine particles are removed or collected, so that the particle size distribution can be obtained. However, since the particle size distribution is sharp in the present invention, the need for such recycling is greatly reduced. In addition, the recycling method of the fine powder of the water-absorbent resin is disclosed in U.S. Pat. Nos. 4,950,692, 5,646482, 5,264,495, 5,478,879, European Patents 081873, 0885917, 0844270, etc. The fine powder recycling method can also be applied to the present invention. The amount of fine powder recycled is 15% by weight or less of the total, preferably 1 to 10% by weight, more preferably 2 to 8% by weight. In the present invention, a water-absorbing resin powder having a sharp particle size distribution can be obtained with high productivity by pulverization, and therefore, a water-absorbing resin powder having a sharper particle size distribution can be obtained by recycling a small amount of fine powder.
[0049]
In the present invention in which cooling is performed before pulverization, the particle size distribution is sharper than before, and the pulverization time for obtaining such a particle size distribution is shortened, and coarse water-absorbent resin powder having a particle size larger than the target particle size is reduced. There is no need to separate the largest particles and fine powder that are not intended, and there is also an effect of reducing the labor of recycling such as re-grinding of coarse particles (for example, 850 μm ON product) and reclassification of fine powder (for example, 150 μm pass product). .
The water-absorbent resin powder after pulverization and classification after cooling is preferably further kept warm or forcedly heated in the next step. The heat-retaining temperature from the outside is in the range of 40 to 100 ° C., and further 50 to 90 ° C. By keeping the water-absorbing resin powder at such a temperature, the handleability of the water-absorbing resin powder is improved, Aggregation and adhesion of the water-absorbent resin powder are also prevented. In the present invention, the dried polymer is deliberately cooled and pulverized or classified to improve the drying efficiency and pulverization efficiency. Separately, the cooled water-absorbent resin powder is kept warm or forcedly heated (reheated). That's fine.
[0050]
In addition, when adding aqueous liquid, especially crosslinking agent aqueous solution by this invention, it is preferable to adjust temperature by further forcibly cooling after pulverization with respect to the water absorbent resin powder obtained by forced cooling before pulverization. The temperature control or cooling means is not particularly limited. However, since the water-absorbent resin powder after pulverization has increased fluidity and specific surface area, the above-described cooling means can be applied more, for example, (1) cooling heat transfer surface If necessary, put into a stirred vessel (hopper) or cylinder and forced cooling, (2) fully cool on a continuous belt, and (3) forced cooling by blowing cold air through the polymer (4) A method of forced cooling simultaneously with transportation using cold air, (5) a low-temperature screw conveyor having a cooling heat transfer surface, etc. are used, but at least the method (1) is preferably used.
[0051]
That is, the temperature of the water-absorbent resin powder before addition of the aqueous liquid is preferably 80 to 35 ° C., more preferably 70 to 35 ° C., still more preferably 60 to 35 ° C. Particularly preferably, the aqueous liquid is added after being cooled (controlled) in the range of 50 to 35 ° C. If the temperature of the water-absorbent resin powder before the addition of the aqueous liquid is high, the mixing of the aqueous liquid becomes non-uniform, and not only it takes time when forcedly cooled or allowed to cool to less than 35 ° C. It is not preferable because it is seen or energy loss during reheating increases.
Since the water-absorbent resin powder obtained as described above has an excellent particle size distribution, it is suitable for further improving physical properties by surface crosslinking. For surface crosslinking, the following forced heating may be performed separately.
[0052]
That is, considering the forced heating process of the water-absorbent resin powder after pulverization and classification, the forced cooling process of the present invention, which seems to be useless in terms of energy and process, is surprisingly effective in drying efficiency and pulverization efficiency. In addition, the mixing property of the aqueous liquid into the obtained water-absorbent resin powder was improved.
The surface cross-linking agent used in the present invention is not particularly limited as long as it is a compound that can react with the functional group of the polymer. Specific examples of the surface cross-linking agent include, for example, polyhydric alcohols such as propylene glycol, glycerin and butanediol, polyhydric epoxy compounds such as ethylene glycol diglycidyl ether (poly) ethyleneimine and the like, Examples include alkylene carbonate compounds, polyvalent oxazoline compounds, haloepoxy compounds and polyamine adducts thereof (polyamide-polyamide epihalohydrin adducts; trademark Kymene; manufactured by Hercules), mono-, di- or polyoxazolidinone compounds, polyvalent metals, etc. It is not limited. Only one type of these surface cross-linking agents may be used, or two or more types may be appropriately mixed and used. When used in combination with the present invention, a surface cross-linking agent comprising a first surface cross-linking agent and a second surface cross-linking agent having different solubility parameters (SP values) among surface cross-linking agents (see US Pat. No. 5,422,405). It is preferable to use it because it is possible to obtain a water-absorbent resin powder that is particularly excellent in absorption capacity under high pressure (eg, 4.90 kPa or more).
[0053]
The amount of the surface cross-linking agent used is appropriately determined depending on the type, reaction conditions, and the like, but is usually 0.001 to 10 parts by weight, preferably 0.1 to 100 parts by weight of the solid content of the water absorbent resin powder. It is used in the range of 01 to 5 parts by weight, more preferably 0.5 to 4 parts by weight.
When mixing the polymer and the surface cross-linking agent, water, water vapor, or an aqueous liquid composed of water and a hydrophilic organic solvent may be added as needed during or after mixing. The amount of water used in this case is 10 parts by weight or less, preferably 0.1 to 100 parts by weight with respect to 100 parts by weight of the solid content of the water-absorbent resin powder, although it depends on the type and particle size of the polymer used. It is in the range of 10 parts by weight, more preferably 1 to 5 parts by weight.
[0054]
Although it does not specifically limit as a hydrophilic organic solvent, For example, methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, t -Lower alcohols such as butyl alcohol; Ketones such as acetone; Ethers such as dioxane and tetrahydrofuran; Amides such as N, N-dimethylformamide; Sulfoxides such as dimethyl sulfoxide.
When mixing the polymer and the surface cross-linking agent, for example, after dispersing the polymer in the aqueous liquid, the surface cross-linking agent may be mixed, or the surface dissolved in water or an aqueous liquid The crosslinking agent may be mixed by spraying or dropping directly on the polymer. Moreover, when mixing using water, you may coexist fine particle-like powder insoluble in water, various organic acids, inorganic acids, surfactant, etc. Among these mixing methods, spray mixing is preferable, and the aqueous liquid at that time is added as fine droplets of 500 μm or less, and further 300 μm or less.
[0055]
In the present invention, when adding an aqueous liquid, the inner wall of the mixer preferably has a temperature exceeding room temperature, and the inner wall temperature of the mixer is 40 ° C. or higher, preferably 45 to 100 ° C., more preferably. Is kept at 50 to 95 ° C., more preferably 55 to 90 ° C., and the inner wall temperature is higher than that of the water absorbent resin powder before addition of the aqueous liquid, preferably 40 ° C. or less, more preferably 20 ° C. or less. A high temperature of 10 ° C. or lower is preferable. In the present invention, the inner wall refers to the inner surface of the mixer including the stirring blade, and in the case of continuous mixing, it is preferable to control the temperature at a steady state temperature, particularly to control the metal part to be essential. .
[0056]
When the inner wall temperature of the mixer is room temperature or lower, even if the temperature of the powder is controlled, the water absorbent resin powder to which an aqueous liquid is added may adhere to the inner wall, or the physical properties of the obtained water absorbent resin powder may deteriorate. If the inner wall temperature is too high, the crosslinking agent in the aqueous solution may be crushed or the aqueous liquid may not be mixed uniformly.
Control of the inner wall temperature of the mixer is not limited as long as the above temperature can be controlled. For example, (1) it may be controlled by external heating such as hot air or a heat medium, or the mixer itself is sufficiently kept warm. In addition, (2) the inner wall of the mixer may be controlled by mixing the powder or aqueous liquid at a specific temperature continuously and in a large amount (for example, 500 kg / hr or more). , (3) The heat of hydration of the water-absorbent resin powder by addition of an aqueous liquid or the frictional heat at the time of mixing may be used, or these may be used in combination, but (1) is preferably used. .
[0057]
Furthermore, in such a method, the mixer having a specific inner wall temperature is preferably a high-speed stirring type mixer having a stirring blade, and usually has a rotational speed of 10 rpm or more, preferably 100 to 10,000 rpm, more preferably 300 to The mixture is stirred and mixed at 5000 rpm, most preferably 500 to 3000 rpm, and the stirring time is usually within 5 minutes, preferably within 3 minutes, more preferably within 1 minute, more preferably within 0.2 minutes. Moreover, an airflow stirring type mixer having a plurality of stirring blades as the mixer is more preferable.
In the method of the present invention, the aqueous liquid is preferably a cross-linking agent aqueous solution because the physical properties are greatly improved by improving the mixing property, and in particular, a cross-linking agent aqueous solution that has conventionally been difficult to mix with a water-absorbent resin is necessary. A polyhydric alcohol aqueous solution containing a crosslinking agent other than a polyhydric alcohol, particularly an aqueous solution containing only a polyhydric alcohol as a crosslinking agent, and / or the aqueous liquid is an organic solvent other than a polyhydric alcohol, particularly a volatile organic solvent When it does not contain, since the effect of this invention is exhibited drastically, it is preferable. When the inner wall temperature of the mixer is increased, the addition of the aqueous liquid of the present invention is suitable for a crosslinking agent that is inert even at the inner wall temperature, for example, a crosslinking agent having a reaction temperature of 110 ° C. or higher required for reheating, particularly a polyhydric alcohol. Applies to In the present invention, the polyhydric alcohol may be used as a cross-linking agent, or may be used as a solvent for the cross-linking agent when used at a reaction temperature or lower, or the functions thereof may be used in combination. In addition, the crosslinking agents other than the polyhydric alcohol used are exemplified in the above-mentioned crosslinking agent and the following literature. Examples of the polyhydric alcohol that most significantly represents the effects of the present invention from the viewpoint of physical properties include polyhydric alcohols having 3 to 8 carbon atoms, and further selected from glycerin, propylene glycol, butanediol, pentanediol, and hexanediol. At least one kind of polyhydric alcohol (wherein the substitution position of the diol does not matter) is preferably used.
[0058]
The volatile organic solvent referred to in the present invention is a solvent having a boiling point equal to or lower than the temperature of the crosslinking reaction described later, particularly an organic solvent having a boiling point of 100 ° C. or lower, and further a boiling point of 85 ° C. or lower. It is preferable to add an aqueous liquid without using these organic solvents because a water-absorbing resin excellent in environmental, cost, and safety can be obtained.
In the present invention, after the polymer and the surface cross-linking agent are mixed, depending on the type of the cross-linking agent, forced heating is performed as necessary to cross-link the vicinity of the polymer surface. The temperature of forced heating is preferably 100 ° C. or higher, more preferably 110 to 230 ° C., and even more preferably 160 to 220 ° C., although depending on the surface cross-linking agent to be used. The range is preferably 1 to 120 minutes, more preferably 5 to 60 minutes. Examples of the apparatus used for forced overheating include a groove type mixer / dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, an airflow dryer, and an infrared dryer. In addition, it is preferable that these heating devices are provided separately from the mixing device and they are connected to each other.
[0059]
These surface cross-linking methods are described in various European patents such as European Patent Nos. 0349240, 0605150, 0450923, 0818733, 0450924, 0668080, and Japanese Patent Application Laid-Open No. 7-242709. Various Japanese patents such as US Pat. No. 7-224304, various US patents such as US Pat. No. 5,409,771, US Pat. No. 5,597,873, US Pat. No. 5,385,983, US Pat. No. 5,610,320, US Pat. No. 5,633,316, US Pat. No., WO99 / 43720, and WO99 / 42496, and these surface cross-linking methods can also be applied to reheating and addition of aqueous liquid in the present invention.
[0060]
  As described above, the present invention is a water-absorbent resin in which an aqueous liquid is added to a powder obtained by heating and drying a hydrogel crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent in a mixer. A method for producing a powder, wherein the heating and drying temperature is in the range of 110 to 230 ° C, and the dry polymer is brought to 80 to 35 ° C before adding the aqueous liquid.ForcedCooling and bulk specific gravity of the dried polymer after grinding(Measured according to JIS K 3362)Further, the present invention provides a method for producing a water-absorbent resin powder, characterized in that the water-absorbing resin powder is 0.65 g / ml or more.
  The present invention also relates to a water-absorbent resin in which an aqueous liquid is added in a mixer to a powder obtained by heating and drying a hydrogel crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent. A method for producing a powder, wherein the heating and drying temperature is in the range of 110 to 230 ° C, and the dry polymer is brought to 80 to 35 ° C before adding the aqueous liquid.ForcedThere is also provided a method for producing a water-absorbent resin powder, characterized by cooling, a mixer / mixer having an inner wall temperature of 40 ° C. or higher, and reheating to 110 to 230 ° C.
[0061]
In these two methods, the larger the difference between the drying temperature and the cooling temperature, the more remarkable the effect of the present invention, and the preferable temperature range is as described above.
The absorption capacity under load (1.96 kPa) and the absorption capacity under no load (physiological saline) of the water absorbent resin powder thus obtained are preferably 25 g / g or more, more preferably 27 g / g or more, and further preferably 30 g / g. g or more, particularly preferably 35 g / g or more. Moreover, the water-soluble component, particle diameter, bulk specific gravity, water absorption ratio and the like are within the above-mentioned ranges.
Further, the absorption capacity under load (4.90 kPa) is preferably 23 g / g or more, more preferably 25 g / g or more, and further preferably 27 g / g or more. In the present invention, such a water-absorbent resin powder having high physical properties can be easily and stably produced.
[0062]
  Moreover, the method for producing the water-absorbent resin powder according to the present invention includes:
  A method for producing a water-absorbent resin powder, wherein a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent is heated and dried and then pulverized.
  Forcibly cooling the dried polymer after heat drying;
  Crushing the dried polymer(Measured according to JIS K 3362)A water absorbent resin powder of 0.65 g / ml or more,
  Further surface cross-linking the cooled water-absorbent resin powder,
It is characterized by.
[0063]
  Moreover, the method for producing the water-absorbent resin powder according to the present invention includes:
  A method for producing a water-absorbent resin powder, wherein a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent is heated and dried and then pulverized.
  Forcibly cooling the dried polymer after heat drying;
  Crushing the dried polymer(Measured according to JIS K 3362)A water absorbent resin powder of 0.65 g / ml or more,
  Adding an aqueous liquid to the cooled water-absorbent resin powder;
  The aqueous liquid is added in a stirred mixer with the inner wall heated,
It is characterized by.
[0065]
In addition to the water-absorbent resin powder of the present invention obtained as described above, if necessary, deodorant, antibacterial agent, fragrance, various inorganic powders, foaming agent, pigment, dye, hydrophilic short fiber, plasticizer Adhesives, surfactants, fertilizers, oxidizing agents, reducing agents, chelating agents, antioxidants, water, water-soluble polymers, binders, salts and the like may be added to impart various functions.
Since the water-absorbent resin powder obtained by including the production method of the present invention is excellent in particle size distribution and physical properties, it can be a water-absorbent resin powder that exhibits higher physical properties by surface cross-linking or subsequent neutralization. Further, in the present invention, such a water-absorbent resin powder can be easily obtained with high productivity and at a low energy cost and without attaching or agglomerating in the production process.
[0066]
For this reason, the water-absorbent resin powder of the present invention can be used in a wide range of applications, but is particularly suitable for sanitary materials / absorbent articles such as disposable diapers / sanitary napkins, and is combined with hydrophilic fiber materials such as pulverized pulp to provide hygiene. It can be preferably used as a material. Moreover, since the water-absorbent resin powder of the present invention has high physical properties, it is suitably used in sanitary materials having a high core concentration (weight ratio of the water-absorbent resin powder to the total amount of fibers and the water-absorbent resin powder) in the sanitary material. For example, the water-absorbent resin powder can be suitably used in a sanitary material having a concentration of 30 to 100% by weight, preferably 40 to 95% by weight or more, and further 50 to 90% by weight.
[0067]
【Example】
BEST MODE FOR CARRYING OUT THE INVENTION
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these. The various performances of the water absorbent resin powder were measured by the following methods. In addition, polymerization, drying, pulverization, and the like in the examples were performed in a series of continuous operations simulating actual production.
(A) Absorption capacity without load
After 0.200 g of the water-absorbent resin powder was uniformly put in a non-woven bag (60 mm × 60 mm) and heat sealed, it was immersed in a large excess (about 200 g) of 0.9 wt% physiological saline at room temperature. After 60 minutes of immersion, the bag was pulled up, drained at 250 G for 3 minutes using a centrifuge, and the weight W1 (g) of the bag was measured. Further, the same operation was performed without using the water absorbent resin powder, and the weight W0 (g) at that time was measured. And from these weight W1 and W0, the water absorption capacity | capacitance (g / g) in no load was computed according to following Formula (a).
[0068]
Water absorption capacity without load (g / g)
= (Weight W1 (g) -Weight W0 (g) -0.2) /0.2 (g)
(B) Water-soluble component amount
The water-absorbent resin powder (1.000 g) was swelled and dispersed in 184.3 g of physiological saline, stirred in a 200 ml beaker for 16 hours, separated from the swollen gel with a filter paper, and filtered. Next, the obtained filtrate was subjected to neutralization titration with a 0.1N (0.1 mol / l) sodium hydroxide aqueous solution and a 0.1N (0.1 mol / l) hydrochloric acid aqueous solution to neutralize and titrate the water absorbent resin powder ( The water-soluble polymer (= water-soluble polyacrylic acid (salt)) in the filtrate dissolved from the swollen gel), that is, the water-soluble component amount (% by weight) of the water-absorbent resin powder was calculated.
[0069]
(C) Solid content of water absorbent resin
Place 1.000 g of water-absorbent resin powder obtained from the dried polymer in an aluminum cup (inner diameter 53 mm × height 23 mm) and re-dry it in a windless oven at 180 ° C. for 3 hours. The solid content (% by weight) of (or dry polymer) was calculated. In addition, about the dry polymer, it was set as solid content of the dry polymer by measuring the solid content by the method similar to the above after grinding | pulverizing.
(D) Particle size distribution and average particle size
The water absorbent resin powder is classified with a JIS standard sieve (850 μm, 600 μm, 300 μm, 150 μm), and the weight of each particle size (850 μm on product / 850-600 μm / 600-300 μm / 300-150 μm / 150 μm pass product) for each sieve. Was measured. Moreover, the weight average particle diameter (D50) was calculated | required by adding the JIS standard sieve if needed, and plotting the particle size distribution of each calculated | required particle size on logarithmic probability paper.
[0070]
(E) Absorption capacity under pressure
According to the methods disclosed in the examples of European Patent 0885917, European Patent 0817873 and European Patent 0811636, 50 g / cm of water-absorbent resin powder to physiological saline2The absorption capacity under pressure at (corresponding to about 4.90 kPa) was measured.
That is, 50 g / cm with respect to 0.900 g of water absorbent resin powder.2While uniformly applying a load of about 4.90 kPa, the weight W2 (g) of physiological saline absorbed by the water-absorbent resin powder over 60 minutes at room temperature was measured using a balance. Then, from the weight W2, the water absorption capacity (g / g) under pressure 60 minutes after the start of absorption is calculated according to the following formula b, and 50 g / cm2The absorption capacity under pressure at (about 4.90 kPa) was used.
[0071]
Formula b: Absorption capacity under pressure (g / g) = weight W2 (g) / weight of water absorbent resin powder (g)
In the same measurement, the load was 20 g / cm.2When measuring at (corresponding to about 1.96 kPa), it is referred to as water absorption capacity under load (1.96 kPa).
(F) Bulk specific gravity
It measured according to JISK3362 using the bulk specific gravity measuring device (made by Kuramochi Scientific Instruments Seisakusho). (See also European Patent Application No. 1029886 / Japanese Patent Application No. 2000-35941 as a method for measuring bulk specific gravity.)
That is, in a room where the temperature is 25 ± 2 ° C. and the relative humidity is 30 to 50%, 120 g of the water-absorbent resin powder is placed in the funnel with the damper closed, and then the damper is quickly opened and the sample is placed in the receiver (100 ml). Dropped. The sample swelled from the receiver was scraped off with a glass rod, and then the weight (g) of the receiver containing the sample was accurately measured to 0.1 g, and the bulk specific gravity (g / ml) was calculated.
[0072]
(G) Impact resistance
According to European Patent No. 0817873 (US Pat. No. 6071976), the impact resistance of the water-absorbent resin powder was vibrated for 30 minutes together with 10.0 g of glass beads and 10.0 g of glass beads. The decline was evaluated.
(H) Weight average particle diameter of the hydrogel crosslinked polymer
The particle size distribution was measured using a 20 wt% saline solution in which only a part of the hydrogel crosslinked polymer (hydrogel) swelled or contracted. That is, 30 g of hydrous gel was dispersed in 1000 g of 20% by weight saline and stirred for 2 hours at 300 rpm using a stirrer chip. Two hours later, the dispersion was put into a 6-layer JIS standard sieve (mesh openings of 9500 μm, 2000 μm, 850 μm, 600 μm, 300 μm, 75 μm / JIS / Z8801 / stainless steel sieve / inner diameter 20 cm), and 6000 g of 20% by weight The hydrogel was classified by sequentially pouring with saline. Next, after thoroughly draining the back side of the sieve with paper, the weight of each particle size of the hydrous gel is determined, the swelling ratio is determined from the total weight (g) and the initial weight (30 g), and the swelling of each particle size (μm) The weight average particle diameter D50 of the hydrogel was determined by converting to the previous particle size (μm) and plotting on logarithmic probability paper.
[0073]
(Production Example 1) ... Polymerization and drying of unneutralized polyacrylic acid crosslinked product
A monomer aqueous solution (1) consisting of 1066.61 g of acrylic acid, 9.12 g of N, N′-methylenebisacrylamide as a copolymerizable cross-linking agent, and 4280.11 g of water can be degassed with nitrogen gas for 60 minutes and then opened and closed. In a closed, closed polymerization vessel.
Next, the upper part of the container was placed under a nitrogen stream, and at a liquid temperature of 23 ° C., 32.27 g of a 10 wt% aqueous solution of 2,2′-azobis (2-amidinopropane) dihydrochloride as a polymerization initiator was added. When 10.66 g of a 10% by weight aqueous solution of hydrogen oxide and 26.64 g of a 1% by weight aqueous solution of L-ascorbic acid were added, the polymerization started after about 5 minutes, and then allowed to stand for 1 hour. Went. The obtained polymer is taken out from the container and subdivided into several mm particles with a meat chopper (made by Hiraga Seisakusho) having a pore diameter of 7.5 mm, thereby forming a particulate hydrogel crosslinked polymer having an average particle diameter of 1500 μm ( 1) was obtained.
[0074]
Next, the particulate hydrogel crosslinked polymer (1) is spread and laminated on a wire mesh having a mesh thickness of about 50 mm and an opening of 300 μm, and then hot air of 135 ° C. (dew point 65 ° C.) is applied in the vertical direction of the gel for 1 m. / Second and aerated for 1 hour to perform hot air drying. In this way, a block-like product comprising a dry polymer (1) in the form of particles having a solid content of 95% by weight was obtained, and the material temperature thereof was about 135 ° C.
(Production Example 2) ... Polymerization and drying of partially neutralized polyacrylic acid crosslinked product
Monomer aqueous solution (2) consisting of 673.79 g of acrylic acid, 5904.7 g of 37 wt% aqueous solution of sodium acrylate, 15.87 g of polyethylene glycol diacrylate (average number of polyethylene glycol units 8) and 714.2 g of water as an internal crosslinking agent ) For 60 minutes with nitrogen gas, and then supply the aqueous solution to a reactor with a lid on a jacketed stainless steel two-arm kneader with two sigma-shaped blades with an internal volume of 10 L and kept at a temperature of 20 ° C. The nitrogen substitution of the reaction system was continued.
[0075]
Next, 19.55 g of a 20% by weight aqueous solution of sodium persulfate and 1.47 g of a 1.0% by weight aqueous solution of L-ascorbic acid were added while rotating the blades. The system reached peak temperature. The hydrogel crosslinked polymer produced at that time was subdivided into a size of about 5 mm. Thereafter, stirring was further continued, and after 60 minutes from the start of polymerization, a particulate hydrogel crosslinked polymer (2) having an average particle diameter of 1600 μm was taken out.
Next, the particulate hydrogel crosslinked polymer (2) is spread and laminated on a wire mesh having a mesh thickness of about 50 mm and an opening of 300 μm, and then hot air of 170 ° C. (dew point 50 ° C.) is applied in the vertical direction of the gel for 1 m. / Second and aerated for 1 hour to perform hot air drying. Thus, a block-like product comprising a dry polymer (2) in the form of particles having a solid content of 96% by weight was obtained, and the material temperature was about 170 ° C.
[0076]
Production Example 3 Polymerization and drying of partially neutralized polyacrylic acid crosslinked product
In Production Example 2, instead of the monomer aqueous solution (2), 425.1 g of acrylic acid, 4497.2 g of a 37% by weight aqueous solution of sodium acrylate, 1.40 g of trimethylolpropane triacrylate as an internal crosslinking agent, and 577. Except for using 7 g monomer aqueous solution (3), aqueous solution polymerization was carried out in a kneader in the same manner as in Production Example 2 to obtain a particulate hydrogel crosslinked polymer (3) having an average particle diameter of 1700 μm. .
Next, in the same manner as in Production Example 2, the particulate hydrogel crosslinked polymer (3) was dried with hot air at 170 ° C. for 1 hour. In this way, a block-like product composed of a dry polymer (3) having a solid content of 95% by weight was obtained, and its material temperature was about 170 ° C.
[0077]
Production Example 4 Polymerization and drying of partially neutralized polyacrylic acid crosslinked product
3. In Production Example 2, instead of the monomer aqueous solution (2), 369 g of acrylic acid, 3907 g of a 37% by weight aqueous solution of sodium acrylate, polyethylene glycol diacrylate (average number of polyethylene glycol units n = 8) as an internal crosslinking agent Except for using the monomer aqueous solution (4) consisting of 99 g and water 1216 g, aqueous solution polymerization is carried out in a kneader in the same manner as in Production Example 2 to obtain a particulate hydrogel crosslinked polymer (4) having an average particle diameter of 1700 μm. Got.
Subsequently, the particulate hydrogel crosslinked polymer (4) was subjected to continuous hot air drying in the same manner as in Production Example 2. Thus, a block-like product comprising a dry polymer (4) in the form of particles having a solid content of 95% by weight was obtained, and the material temperature was about 170 ° C.
[0078]
(Production Example 5) Polymerization and drying of partially neutralized polyacrylic acid crosslinked product
100 parts of acrylic acid, 656.4 parts of 37 wt% sodium acrylate aqueous solution, 0.77 parts of polyethylene glycol diacrylate (average number of polyethylene glycol units n = 8), and 216.7 parts of deionized water are sufficiently mixed. A monomer aqueous solution (5) was prepared. The monomer aqueous solution (5) thus obtained was continuously fed at 290 kg / h with a metering pump, and nitrogen gas was continuously blown in the middle of the piping to reduce the oxygen concentration of the monomer aqueous solution (5) to 0.5 ppm or less. I made it. Further, 2,2′-azobis (amidinopropane) dihydrochloride (trade name V-50, manufactured by Wako Pure Chemical Industries, Ltd.), sodium persulfate, L-ascorbic acid and hydrogen peroxide were added to the monomer aqueous solution (5). Four kinds of aqueous initiator solutions are sequentially line-mixed (0.08 parts / 0.08 parts / 0.008 parts / 0.006 parts in terms of initiator solid content (components)) and moved at 12 cm / min. An endless belt polymerization machine (having a flat belt having a weir of 50 mm on both sides) was continuously fed to a thickness of 25 mm. By immediately starting the polymerization, the polymer thus obtained is discharged from the end of the belt polymerization machine, further cut into about 5 to 10 cm pieces by a continuous cutting machine, and then pulverized with a meat chopper (pore diameter 9 mm) A particulate hydrogel crosslinked polymer (5) having an average particle diameter of 1600 μm was obtained.
[0079]
Next, the particulate hydrogel crosslinked polymer (5) is loaded on a punching metal to a thickness of 50 mm, and continuously heated with a belt dryer (hot air at 180 ° C. (dew point 60 ° C.) for 20 minutes in the vertical direction) Went. Thus, a block-like product comprising a dry polymer (5) having a solid content of 94% by weight was obtained, and its material temperature was about 180 ° C.
Example 1 Forced cooling of dried polymer (1) to 60 ° C.
Instead of hot air, cold air at room temperature (1 m / sec) was vented vertically to the block-like product (material temperature of about 135 ° C.) of the dry particulate polymer (1) obtained in Production Example 1. By doing so, the block-like product of the particulate dry polymer (1) was forcibly cooled to 60 ° C. and then taken out from the air-cooled cooling device. At the same time as taking out, block aggregates on the wire mesh were crushed, and within 30 seconds, the obtained particulate dried product (1) was converted into a three-stage roll granulator (with a roll gap of 1.0 mm / 0.45 mm / 0.25 mm). When drying, the block of the dried polymer (1) has very good peelability from the 300 μm mesh, and the particle size distribution of the water-absorbent resin powder (1) obtained by pulverization is shown in Table 1. .
[0080]
Example 2 Forced cooling to 45 ° C
In Example 1, the block-like product was forcibly cooled to 45 ° C. by adjusting the time for cooling air to flow, and then crushed in the same manner as in Example 1, and the obtained particulate dried product (2) was similarly used. To grind. During drying, the peelability of the dried polymer (1) from the block 300 μm wire mesh is very good, and the particle size distribution of the water-absorbent resin powder (2) obtained by pulverization is shown in Table 1. .
Example 3 Forced cooling to 95 ° C
In Example 1, the block-like product was forcibly cooled to 95 ° C. by adjusting the time for cooling air to pass through, and then crushed in the same manner as in Example 1, and the obtained particulate dried product (3) was similarly used. To grind. During drying, the peelability of the dry polymer (1) from the block 300 μm wire mesh is slightly worse than those of Examples 1 and 2, but the water-absorbent resin powder (3) obtained by pulverization is good. The particle size distribution is shown in Table 1.
[0081]
Example 4 Forced cooling to 80 ° C.
In Example 1, the block-like product was forcibly cooled to 80 ° C. by adjusting the time for cooling air to flow, and then crushed in the same manner as in Example 1, and the obtained particulate dried product (4) was similarly used. To grind. During drying, the peelability of the dry polymer (1) from the block 300 μm mesh was slightly better than that of Examples 1 and 2, but the water-absorbent resin powder (4) obtained by pulverization was good. The particle size distribution is shown in Table 1.
(Example 5) ... Forced cooling of dried polymer (2) to 40 ° C
Instead of hot air, cold air at room temperature (1 m / sec) was ventilated in the vertical direction to the block-shaped product (material temperature: about 170 ° C.) of the particulate dry polymer (2) obtained in Production Example 2. By doing so, the block-like product of the particulate dry polymer (2) was forcibly cooled to 40 ° C. and then taken out from the air-cooled cooling device. At the same time as taking out, block aggregates on the wire mesh were crushed, and within 30 seconds, the obtained particulate dried product (5) was converted into a three-stage roll granulator (with a roll gap of 1.0 mm / 0.45 mm / 0.25 mm). During drying, the peelability of the dried polymer (2) from the block 300 μm wire mesh was very good, and the particle size distribution of the water-absorbent resin powder (5) obtained by grinding was shown in Table 1. Shown in
[0082]
(Example 6) ... Aqueous liquid addition and reheating
To 100 parts by weight of the water-absorbent resin powder (5) obtained by including the forced cooling step, 1,4-butanediol / propylene glycol / water / isopropanol = 0.32 / 0.50 / at a powder temperature of 35 ° C. A solution of a surface cross-linking agent consisting of 2.73 / 0.45 (parts by weight) was mixed, and further reheated at 210 ° C. for 30 minutes to obtain a surface cross-linked water-absorbent resin powder (6). . The water absorption capacity of the water absorbent resin powder (6) under no load was 28 g / g, and the water absorption capacity under pressure (4.90 kPa) was 25 g / g.
[0083]
In addition, about the water absorbent resin powder (5) obtained in Example 5, the water absorption capacity | capacitance and the amount of water-soluble components in the no-load were measured, and were 31 g / g and 5 weight%, respectively. The bulk density of the water absorbent resin powder (5) before addition of the aqueous liquid was 0.67 g / ml, and the temperature was 35 ° C.
(Example 7) ... post-neutralization
The water-absorbing resin powder (1) obtained in Example 1 and a predetermined amount of sodium carbonate powder were dry blended (powder mixed) to post-neutralize the carboxyl groups, thereby neutralizing 75 mol% water absorption. Resin powder (7) was obtained. The water absorption capacity of the water absorbent resin powder (7) under no load was 42 g / g, and the water-soluble component amount was 3% by weight.
[0084]
Furthermore, when the water-absorbent resin powders (2) to (4) obtained in Examples 2 to 4 were also post-neutralized, the water absorption capacity without load was 42 g / g, and the amount of water-soluble components was 3 wt. %Met.
(Comparative Example 1) ... No forced cooling
In Example 1, the dried polymer (1) obtained in Production Example 1 was taken out of the dryer without using cold air ventilation, and at the same time, the block-like product was crushed in the same manner as in Example 1 and obtained. The comparative particulate dried product (1) (temperature of 120 ° C. during pulverization) was similarly pulverized. When drying, the block of the dried polymer (1) has poor releasability from the 300 μm wire mesh, the dried polymer (1) particles are clogged into the wire mesh, and the drying efficiency during continuous drying (Uniformity and drying speed) decreased. Table 1 shows the particle size distribution of the comparative water absorbent resin powder (1) obtained by pulverization.
[0085]
(Comparative Example 2) ... No forced cooling
In Example 5, the dried polymer (2) obtained in Production Example 2 was taken out of the dryer without using cold air ventilation, and at the same time, the block-like product was crushed in the same manner as in Example 1 and obtained. The comparative particulate dried product (2) (temperature of 120 ° C. during pulverization) was similarly pulverized. When drying, the block of the dried polymer (2) is poorly peelable from the 300 μm wire mesh, and the dry polymer (2) particles are clogged into the wire mesh, and the drying efficiency during continuous drying (Uniformity and drying speed) were reduced. Table 1 shows the particle size distribution of the comparative water absorbent resin powder (2) obtained by pulverization.
[0086]
(Comparative Example 3) ... Addition of aqueous liquid and post-heating / without forced cooling
To the comparative water absorbent resin powder (2) obtained in Comparative Example 2 (without forced cooling of the dried polymer (2)), an aqueous liquid was added in the same manner as in Example 6 (with forced cooling of the polymer). did. In the comparative water absorbent resin powder (2) that is not cooled to 35 to 80 ° C., even if it is adjusted to the same particle size as the water absorbent resin powder (5), since the powder temperature is high, the aggregation and adhesion in the mixer gradually As seen, continuous mixing was difficult.
Example 8 Forced cooling of dry polymer (3)
Instead of hot air, a cold air at room temperature (1 m / second) was passed in the vertical direction to the block-like product (material temperature: about 170 ° C.) of the particulate dry polymer (3) obtained in Production Example 3. By doing so, the block-like product of the particulate dry polymer (3) was forcibly cooled to 50 ° C. and then taken out from the air-cooled cooling device. At the same time as taking out, block aggregates on the wire mesh were crushed, and within 30 seconds, the obtained particulate dried product (6) was converted into a three-stage roll granulator (roll gap of 1.0 mm / 0.45 mm from the top). /0.10 mm). During drying, the peelability of the dried polymer (3) from the 300 μm wire mesh was very good, and the particle size distribution of the water-absorbent resin powder (8) obtained by grinding was shown in Table 1. Shown in The water absorption capacity of the water absorbent resin powder (8) under no load was 44 g / g, and the amount of water-soluble component was 17% by weight.
[0087]
(Embodiment 9) ... Same / Crushing condition change
In Example 8, the grinding conditions for the dried polymer (6) were changed. That is, the particulate dried product (6) was pulverized with a pin mill (Fuji Paudal Kogyo Sample Mill KII-1) (850 to 150 μm is 85% by weight), and further a morphogenizer (manufactured by Nippon Seiki Co., Ltd., high-speed homogenizer; MX The surface was polished by −7) to obtain a water absorbent resin powder (9). The particle size distribution is shown in Table 1.
(Example 10) ... Addition of aqueous liquid to bulk specific gravity 0.74 g / ml
Propylene glycol with respect to 100 parts by weight of water absorbent resin powder (9A) (bulk specific gravity 0.74 g / ml) at a temperature of 40 ° C. obtained by classifying the water absorbent resin powder (9) obtained in Example 9 to 300 to 150 μm. An aqueous liquid consisting of /water/ethanol=0.3/2.5/1 (parts by weight) is sprayed and added in a high-speed mixer, and further stirred in an oil bath at 210 ° C. and heat-treated for 30 minutes. A surface-crosslinked water-absorbing resin powder (10) was obtained. Table 2 shows the water absorption capacity under no load, the absorption capacity under pressure (1.96 kPa), and the same (4.90 kPa). Furthermore, the value of the absorption capacity under pressure after the impact resistance test is indicated by ().
[0088]
Example 11 Addition of aqueous liquid to bulk specific gravity 0.63 g / ml
Similar to Example 10 with respect to the water absorbent resin powder (8A) (bulk specific gravity 0.63 g / ml) at a temperature of 40 ° C. obtained by classifying the water absorbent resin powder (8) obtained in Example 8 to 300 to 150 μm. An aqueous liquid was added to the mixture, followed by heat treatment for 30 minutes. Table 2 shows the analysis results of the water absorbent resin powder (11) obtained.
(Example 12) ... Addition of aqueous liquid to bulk specific gravity 0.73 g / ml
With respect to 100 parts by weight of the water-absorbent resin powder (9B) (bulk specific gravity 0.73 g / ml) at a temperature of 40 ° C. obtained by classifying the water-absorbent resin powder (9) obtained in Example 9 into 500 to 150 μm. An aqueous liquid was added in the same manner as in 10 and 11, and heat treatment was further performed for 25 minutes. Table 2 shows the analysis results of the water absorbent resin powder (12) obtained.
[0089]
Example 13 Addition of aqueous liquid to bulk specific gravity of 0.63 g / ml
With respect to the water-absorbent resin powder (8B) (bulk specific gravity 0.63 g / ml) at a temperature of 40 ° C. obtained by classifying the water-absorbent resin powder (8) obtained in Example 8 to 500 to 150 μm, Examples 10 to 12 were used. An aqueous liquid was added in the same manner as above, followed by heat treatment for 25 minutes. Table 2 shows the analysis results of the water absorbent resin powder (13) obtained.
Example 14 Forced cooling of dry polymer (4)
Instead of hot air, cold air at room temperature (1 m / sec) was vented vertically to the block-like product (material temperature of about 170 ° C.) of the particulate dry polymer (4) obtained in Production Example 4. By doing so, the block-like product of the particulate dry polymer (4) was forcibly cooled to 65 ° C. and then taken out from the air-cooled cooling device. At the same time as taking out, block aggregates on the wire mesh were crushed, and within 30 seconds, the obtained particulate dried product (8) was converted into a three-stage roll granulator (roll gap 1.0 mm / 0.45 mm from the top). /0.09 mm). During drying, the peelability of the dried polymer (4) from the block 300 μm wire mesh was very good. The resultant water-absorbent resin powder (14) has a water absorption capacity under load of 43 g / g, a water-soluble component amount of 10% by weight, and its particle size distribution is shown in Table 1.
[0090]
(Example 15) ... Addition of aqueous liquid and post-heating / powder temperature 60 ° C
An aqueous solution composed of ethylene glycol diglycidyl ether / propylene glycol / water = 0.1 / 3/1 (% by weight) was externally heated to 500 g of the water absorbent resin powder (14) having a temperature of 60 ° C. obtained in Example 14. When mixing at a high speed (rotation speed: 320 rpm) in a Readyge mixer (M5R; manufactured by Lodige) with the inner wall temperature controlled to 60 ° C., there is almost no adhesion of water-absorbing resin powder without using an organic solvent. It was. Furthermore, the mixture was stirred and heated in a 5 L mortar mixer (manufactured by Nishinippon Seisakusho) for 50 minutes in an oil bath at 205 ° C. to obtain surface-crosslinked water-absorbent resin powder (15). The results are shown in Table 2.
[0091]
(Example 16) ... Addition of aqueous liquid and post-heating / powder temperature 40 ° C
The water absorbent resin powder (14) having a temperature of 60 ° C. obtained in Example 14 was continuously air-cooled to cool the temperature to 40 ° C. Hereinafter, when the aqueous liquid was added in the same manner as in Example 15 using the water absorbent resin powder (14) at a temperature of 40 ° C., the adhesion to the mixer was further reduced. The obtained mixture was heated in the same manner as in Example 12 to obtain a water absorbent resin powder (16). The analysis results are shown in Table 2.
Example 17: Aqueous liquid addition and post-heating / mixer inner wall at room temperature
In Example 14, the external heating of the mixer was stopped and the aqueous liquid was added with a room temperature mixer, and the adhesion to the inner wall was greatly increased and the continuous operability was lowered.
[0092]
Example 18 Forced cooling of dry polymer (5)
Instead of hot air, cold air (1 m / s) at room temperature was vertically applied to the block-like product (material temperature of about 180 ° C.) made of the particulate dry polymer (5) obtained in Production Example 5. By continuously feeding, the block-like product of the particulate dry polymer (5) was forcibly cooled to 60 ° C., then taken out from the continuous belt air-cooled cooling device, and further the dry polymer (5) was 100 kg / h. In this way, continuous polymerization, continuous drying, and continuous pulverization were performed by continuously supplying to a roll pulverizer. During drying, the peelability of the dried polymer (5) from the punching metal is very good, and the particle size distribution of the water absorbent resin powder (18) obtained by pulverization is shown in Table 1. The water absorption capacity of the water absorbent resin powder (18) under no load was 55 g / g, and the water-soluble content was 6% by weight.
[0093]
In addition, the cold air used for forced cooling of the block-like product of the particulate dry polymer (5) was heated to about 90 ° C. by using this forced cooling. It supplied to the air supply port of the belt hot-air dryer of Example 5, and performed continuous drying of Production Example 5 as a raw material of hot air (180 ° C.) used for drying. Thus, in the hot air drying of Production Example 5, instead of using room temperature air, hot air of 180 ° C. is manufactured using hot air of about 90 ° C., so that energy saving is significant and hot air (exhaust gas) ) Is not discharged into the environment.
(Example 19) ... Aqueous liquid addition and post-heating / powder temperature 50 ° C
The water-absorbent resin powder (18) obtained through the forced cooling step in Example 18 was supplied to a high-speed continuous mixer (turbulator / 1000 rpm) at a powder temperature of 50 ° C. at 100 kg / h. The powder (18) was sprayed with a surface cross-linking agent aqueous solution composed of 1,4-butanediol / propylene glycol / water / isopropanol = 0.32 / 0.50 / 2.73 / 0.51 (wt% / powder). Sprayed at about 250 μm. Subsequently, the obtained mixture was subjected to continuous reheating treatment at 195 ° C. for 40 minutes to obtain a surface-crosslinked water-absorbing resin powder (19). The results are shown in Table 2. In addition, the inner wall temperature of the high-speed continuous mixer (turbulizer) at the time of continuous mixing was about 70 to 80 ° C. in terms of powder temperature and frictional heat, and was hardly adhered because it was heated.
[0094]
(Example 20) Aqueous liquid addition and post-heating / powder temperature 50 ° C
In Example 19, the surface cross-linking agent aqueous solution was changed to a surface cross-linking agent aqueous solution consisting of ethylene glycol diglycidyl ether / propylene glycol / water / isopropanol = 0.03 / 1/3 / 0.9 (wt% / powder). The water-absorbing resin powder (18) was sprayed and further subjected to continuous reheating treatment at 190 ° C. for 35 minutes to obtain a surface-crosslinked water-absorbing resin powder (20). The results are shown in Table 2.
(Example 21) ... Addition of aqueous liquid and post-heating / powder temperature 30 ° C
Except for further cooling the water-absorbent resin powder (18) obtained in Example 18 to a powder temperature of 30 ° C., a surface cross-linking agent aqueous solution was mixed in the same manner as in Example 19 and then continuously reconstituted at 195 ° C. for 40 minutes. Heat treatment was performed. By cooling to a powder temperature of 30 ° C., when the operation was continued for a long time, some aggregation was observed during continuous mixing and transportation, and the reaction time was slightly increased. The results are shown in Table 2.
[0095]
(Comparative Example 4) ... Addition of aqueous liquid and post-heating / without forced cooling
In Example 14, the comparative water-absorbent resin powder (3) was obtained by taking out the dried polymer (4) from the dryer and pulverizing it immediately without forced cooling. Next, in Example 15, an aqueous liquid was similarly added to the comparative water absorbent resin powder (3) whose particle size was adjusted to 850 μm or less instead of the water absorbent resin powder (14). In the comparative water absorbent resin powder (3) that was not forcedly cooled to 40 to 80 ° C., even when the particle size was adjusted to the same as in Example 15, aggregation and adhesion in the mixer were gradually observed, and continuous operation was difficult. It was. The results are shown in Table 2.
[0096]
(Comparative Example 5) ... Grinding of dry polymer (5) / without forced cooling
In Example 18, the dried polymer (5) was supplied to the same roll crusher as in Example 18 without forced cooling. Two hours after the start of continuous grinding, abnormal noise of the pulverizer derived from aggregates and adhesion of aggregates began to occur. Table 1 shows the particle size distribution of the comparative water absorbent resin powder (5) obtained by pulverization.
(Comparative Example 6) ... Addition of aqueous liquid and post-heating / without forced cooling
In Example 19, it was surface-crosslinked by carrying out similarly to Example 19 except using the comparative water absorbent resin powder (5) obtained in Comparative Example 5 instead of the water absorbent resin powder (19). A comparative water absorbent resin powder (6) was obtained. The results are shown in Table 2.
[0097]
(Example 22) ... Preparation of sanitary materials
50 parts by weight of the surface-crosslinked water absorbent resin powder (19) obtained in Example 19 and 50 parts by weight of pulverized wood pulp were dry-mixed using a mixer. Next, the resulting mixture was formed into a 12 cm × 38 cm web by air blowing. Pressure 2kg / cm2By pressing at about 193 kPa, the basis weight is about 526 g / m.2The absorber (1) was obtained. Next, by incorporating the absorbent body (1) between the bag sheet (liquid impermeable sheet) having leg gathers and the liquid permeable top sheet, a paper diaper (1) having a weight of 47 g and a core concentration of 50% by weight was produced. .
[0098]
20g / cm for disposable diapers (1)2When a load of (about 1.93 kPa) is applied with a flat plate weight and physiological saline is injected under pressure from the hole in the center of the plate, it is obtained from the water absorbent resin powder (19) obtained through the cooling step. The disposable diaper (1) showed a saturated absorption capacity of about 470 g.
(Comparative example 7) ... Creation of sanitary materials
In Example 22, a comparative paper diaper (1) was obtained in the same manner as in Example 22 except that the comparative water absorbent resin powder (6) obtained in Comparative Example 6 was used instead of the water absorbent resin powder (19). Got. Comparative paper diaper (1) is 20 g / cm as in Example 22.2When a load of (about 1.93 kPa) was applied with a flat plate-like weight and physiological saline was injected under pressure from the hole in the center of the plate, it showed a saturated absorption capacity of about 410 g, and the comparative paper diaper (1) was cooled. It was inferior to the paper diaper (1) obtained from the water-absorbent resin powder (19) which passed through the process.
[0099]
[Table 1]
Figure 0004676625
[0100]
[Table 2]
Figure 0004676625
[0101]
In Examples 1 to 7 and Example 14 shown in Table 1, the average particle diameter of the water-absorbent resin powder after pulverization is in the range of 200 μm to 600 μm, and the ratio of particles of 150 μm or less to 850 μm or more is 15% by weight. It turns out that it is the preferable range in this invention called the following. On the other hand, in Comparative Examples 1 and 2, the average particle diameter of the water-absorbent resin powder after pulverization is out of the range of 200 μm to 600 μm, and the ratio of particles of 150 μm or less to 850 μm or more exceeds 15% by weight. I understand.
In addition, from the results shown in Table 1, the present invention forcibly cools the dried polymer after heating and drying, preferably forcibly cooling to 85 to 35 ° C, more preferably 80 to 40 ° C, and even more preferably 70 to 45 ° C. In Examples 1-5, compared with the comparative examples 1 and 2 of the present invention in which forced cooling is not performed, ON products (850 μm or more) deviating from a predetermined particle size are greatly reduced, and in the present invention, the average particle size and particle size distribution are excellent. I understand that
[0102]
From the results shown in Table 1, it can be seen that in the present invention, the adhesion of the dry polymer to the wire mesh and clogging are also reduced, and the drying efficiency (drying speed, uniformity) is increased. It can also be seen that there is no significant difference between 40 ° C. and 60 ° C., and that it is sufficient up to 60 ° C. in view of the size of the cooling facility. Further, although not shown in the table, the water-absorbent resin powder of the present invention also shows an advantage that there is little aggregation after pulverization.
From the results shown in Table 2, it can be seen that in the present invention, the addition of the aqueous liquid is uniform and the physical properties are excellent. Moreover, when the bulk specific gravity after grinding | pulverization is 0.65 g / ml or more by the comparison of Examples 10-13, it turns out that the water absorption capacity | capacitance under pressure (especially 4.90 kPa) improves more. As shown in () of the table, the absorption capacity under pressure (1.93 kPa and 4.90 kPa) hardly decreases even after impact, and the impact resistance and liquid permeability are excellent. Comparison of Examples 15 to 17 shows that the temperature of the powder and the temperature of the inner wall of the mixer are important for the addition of the aqueous liquid.
[0103]
Furthermore, although the said Example is compared by a series of continuous operation, the effect of this invention is 1 t / day or more with water-absorbent resin powder per line especially when producing continuously, Preferably it is 10 t / day or more. When continuous drying, continuous pulverization, and subsequent addition of an aqueous liquid, it becomes more prominent.
It should be noted that the specific embodiments or examples made in the detailed description of the invention are intended to clarify the technical contents of the present invention, and are limited to such specific examples in a narrow sense. It should be understood that the invention can be practiced with various modifications within the spirit of the invention and the scope of the following claims.
[Brief description of the drawings]
FIG. 1 is a process diagram showing a typical example of a process for producing a water absorbent resin powder of the present invention. The present invention is suitable for continuous processes including polymerization, drying, and grinding, and an example thereof is shown.

Claims (25)

架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕する吸水性樹脂粉末の製造方法であって、
当該粉砕後の吸水性樹脂粉末の重量平均粒子径が２００〜６００μｍの範囲であり、さらに１５０μｍ以下ないし８５０μｍ以上の粒子の合計割合が１５重量％以下であり、
加熱乾燥後の乾燥重合体を粉砕前または粉砕時に強制冷却すること、
を特徴とする、吸水性樹脂粉末の製造方法。A method for producing a water-absorbent resin powder, wherein a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent is heated and dried and then pulverized.
The weight average particle diameter of the water-absorbent resin powder after pulverization is in the range of 200 to 600 μm, and the total ratio of particles of 150 μm or less to 850 μm or more is 15% by weight or less,
Forcibly cooling the dried polymer after heat drying before or during crushing ;
A method for producing a water-absorbent resin powder, characterized in that: 粉砕後の吸水性樹脂粉末を、さらに表面架橋する、請求項１に記載の吸水性樹脂粉末の製造方法。  The method for producing a water-absorbent resin powder according to claim 1, wherein the water-absorbent resin powder after pulverization is further subjected to surface crosslinking. 加熱乾燥の温度が１１０〜２３０℃の範囲であり、加熱乾燥後の強制冷却の温度が８５〜３５℃であり、粉砕後の表面架橋の温度が１１０〜２３０℃である、請求項２に記載の吸水性樹脂粉末の製造方法。  The temperature of heat drying is in the range of 110 to 230 ° C, the temperature of forced cooling after heat drying is 85 to 35 ° C, and the temperature of surface crosslinking after pulverization is 110 to 230 ° C. Manufacturing method of water-absorbent resin powder. 乾燥重合体の固形分が９３〜９７重量％である、請求項１から３までのいずれかに記載の吸水性樹脂粉末の製造方法。  The method for producing a water-absorbent resin powder according to any one of claims 1 to 3, wherein the dry polymer has a solid content of 93 to 97% by weight. 含水ゲル状架橋重合体が１〜２０ｃｍの一定厚みに粒子状で積層されて乾燥される、請求項１から４までのいずれかに記載の吸水性樹脂粉末の製造方法。  The method for producing a water-absorbent resin powder according to any one of claims 1 to 4, wherein the water-containing gel-like crosslinked polymer is laminated in a particulate form with a constant thickness of 1 to 20 cm and dried. 乾燥重合体の強制冷却によって得られた熱が再利用される、請求項１から５までのいずれかに記載の吸水性樹脂粉末の製造方法。  The method for producing a water-absorbent resin powder according to any one of claims 1 to 5, wherein heat obtained by forced cooling of the dried polymer is reused. 粉砕後の吸水性樹脂粉末の嵩比重（ＪＩＳ Ｋ ３３６２に準じて測定）が０．６５ｇ／ｍｌ以上である、請求項１から６までのいずれかに記載の吸水性樹脂粉末の製造方法。The method for producing a water-absorbent resin powder according to any one of claims 1 to 6, wherein the pulverized water-absorbent resin powder has a bulk specific gravity (measured according to JIS K 3362) of 0.65 g / ml or more. 粉砕後、得られた吸水性樹脂粉末をさらに強制加熱ないし保温する、請求項１から７までのいずれかに記載の吸水性樹脂粉末の製造方法。  The method for producing a water absorbent resin powder according to any one of claims 1 to 7, wherein the obtained water absorbent resin powder is further forcibly heated or kept warm after pulverization. 強制冷却後に粉砕した後、得られた吸水性樹脂粉末にさらに水性液を添加する、請求項１から８までのいずれかに記載の吸水性樹脂粉末の製造方法。  The method for producing a water absorbent resin powder according to any one of claims 1 to 8, wherein an aqueous liquid is further added to the obtained water absorbent resin powder after pulverization after forced cooling. 架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕する吸水性樹脂粉末の製造方法であって、
加熱乾燥後の乾燥重合体を強制冷却して得られた熱を吸水性樹脂の製造工程における強制加熱に再利用すること、
を特徴とする、吸水性樹脂粉末の製造方法。A method for producing a water-absorbent resin powder, wherein a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent is heated and dried and then pulverized.
Reusing the heat obtained by forcibly cooling the dried polymer after heat drying for forced heating in the production process of the water absorbent resin ;
A method for producing a water-absorbent resin powder, characterized in that: 架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕して得られた粉末に混合機中で水性液を添加する吸水性樹脂粉末の製造方法であって、
加熱乾燥温度が１１０〜２３０℃の範囲であること、水性液添加前に乾燥重合体を８０〜３５℃に強制冷却すること、および、粉砕後の乾燥重合体の嵩比重（ＪＩＳ Ｋ ３３６２に準じて測定）を０．６５ｇ／ｍｌ以上とすること、
を特徴とする、吸水性樹脂粉末の製造方法。This is a method for producing a water-absorbent resin powder in which an aqueous liquid is added in a mixer to a powder obtained by heating and drying a hydrogel crosslinked polymer obtained by polymerizing an aqueous monomer solution containing a crosslinking agent. And
The heating and drying temperature is in the range of 110 to 230 ° C., the dried polymer is forcibly cooled to 80 to 35 ° C. before adding the aqueous liquid, and the bulk specific gravity of the dried polymer after pulverization (according to JIS K 3362). Measurement) to be 0.65 g / ml or more ,
A method for producing a water-absorbent resin powder, characterized in that: 乾燥重合体の強制冷却が粉砕前になされる、請求項１１に記載の吸水性樹脂粉末の製造方法。  The method for producing a water-absorbent resin powder according to claim 11, wherein forced cooling of the dry polymer is performed before pulverization. 水性液が架橋剤水溶液である、請求項９または１１に記載の吸水性樹脂粉末の製造方法。The method for producing a water absorbent resin powder according to claim 9 or 11, wherein the aqueous liquid is an aqueous crosslinking agent solution. 水性液が多価アルコール水溶液である、請求項９または１１に記載の吸水性樹脂粉末の製造方法。The method for producing a water-absorbent resin powder according to claim 9 or 11 , wherein the aqueous liquid is a polyhydric alcohol aqueous solution. 最終的に得られる吸水性樹脂粉末の重量平均粒子径が２００〜６００μｍの範囲であり、さらに１５０μｍ以下ないし８５０μｍ以上の粒子の合計割合が１５重量％以下である、請求項１から１４までのいずれかに記載の吸水性樹脂粉末の製造方法。The weight average particle diameter of the finally obtained water-absorbent resin powder is in the range of 200 to 600 µm, and the total proportion of particles of 150 µm or less to 850 µm or more is 15 wt% or less. A method for producing the water-absorbent resin powder according to claim 1. 架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕して得られた粉末に混合機中で水性液を添加する吸水性樹脂粉末の製造方法であって、
加熱乾燥温度が１１０〜２３０℃の範囲であること、水性液添加前に乾燥重合体を８０〜３５℃に強制冷却すること、および、混合機の内壁温度が４０℃以上の攪拌混合機であること、および、１１０〜２３０℃に再加熱すること、
を特徴とする、吸水性樹脂粉末の製造方法。This is a method for producing a water-absorbent resin powder in which an aqueous liquid is added in a mixer to a powder obtained by heating and drying a hydrogel crosslinked polymer obtained by polymerizing an aqueous monomer solution containing a crosslinking agent. And
It is a stirring mixer whose heating and drying temperature is in the range of 110 to 230 ° C., forcibly cooling the dried polymer to 80 to 35 ° C. before adding the aqueous liquid, and whose inner wall temperature of the mixer is 40 ° C. or higher. it, and reheating to one hundred and ten to two hundred thirty ° C.,
A method for producing a water-absorbent resin powder, characterized in that: 架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕する吸水性樹脂粉末の製造方法であって、
加熱乾燥後の乾燥重合体を強制冷却すること、
乾燥重合体を粉砕して嵩比重（ＪＩＳ Ｋ ３３６２に準じて測定）０．６５ｇ／ｍｌ以上の吸水性樹脂粉末とすること、
冷却された吸水性樹脂粉末をさらに表面架橋すること、
を特徴とする、吸水性樹脂粉末の製造方法。A method for producing a water-absorbent resin powder, wherein a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent is heated and dried and then pulverized.
Forcibly cooling the dried polymer after heat drying;
Pulverizing the dried polymer to obtain a water-absorbent resin powder having a bulk specific gravity (measured according to JIS K 3362) of 0.65 g / ml or more,
Further surface cross-linking the cooled water-absorbent resin powder,
A method for producing a water-absorbent resin powder, characterized in that: 架橋剤を含む単量体水溶液を重合してなる含水ゲル状架橋重合体を加熱乾燥した後に粉砕する吸水性樹脂粉末の製造方法であって、
加熱乾燥後の乾燥重合体を強制冷却すること、
乾燥重合体を粉砕して嵩比重（ＪＩＳ Ｋ ３３６２に準じて測定）０．６５ｇ／ｍｌ以上の吸水性樹脂粉末とすること、
冷却された吸水性樹脂粉末にさらに水性液を添加すること、
水性液が内壁が加熱された攪拌混合機で添加されること、
を特徴とする、吸水性樹脂粉末の製造方法。A method for producing a water-absorbent resin powder, wherein a water-containing gel-like crosslinked polymer obtained by polymerizing a monomer aqueous solution containing a crosslinking agent is heated and dried and then pulverized.
Forcibly cooling the dried polymer after heat drying;
Pulverizing the dried polymer to obtain a water-absorbent resin powder having a bulk specific gravity (measured according to JIS K 3362) of 0.65 g / ml or more,
Adding an aqueous liquid to the cooled water-absorbent resin powder;
The aqueous liquid is added in a stirred mixer with the inner wall heated,
A method for producing a water-absorbent resin powder, characterized in that: 乾燥重合体の強制冷却が冷風を前記乾燥重合体に通気することにより行われる、請求項１から１８までのいずれかに記載の吸水性樹脂粉末の製造方法。The method for producing a water-absorbent resin powder according to any one of claims 1 to 18, wherein forced cooling of the dry polymer is performed by passing cold air through the dry polymer. 冷風の温度が６０℃以下である、請求項１９に記載の吸水性樹脂粉末の製造方法。The method for producing a water-absorbent resin powder according to claim 19, wherein the temperature of the cold air is 60 ° C or lower. 水性液が多価アルコール水溶液である、請求項１６または１８に記載の吸水性樹脂粉末の製造方法。The method for producing a water-absorbent resin powder according to claim 16 or 18, wherein the aqueous liquid is a polyhydric alcohol aqueous solution. １ラインあたり、吸水性樹脂粉末が１ｔ／日以上の大スケールで連続乾燥、連続粉砕およびその後の連続水性液添加を行う、請求項１から２１までのいずれかに記載の吸水性樹脂粉末の製造方法。The production of the water-absorbent resin powder according to any one of claims 1 to 21, wherein the water-absorbent resin powder is continuously dried, continuously pulverized and subsequently added with a continuous aqueous liquid on a large scale of 1 t / day or more per line. Method. 得られる吸水性樹脂粉末の加圧下吸収倍率（１．９６ｋＰａ）が２５ｇ／ｇ以上である、請求項１から２２までのいずれかに記載の吸水性樹脂粉末の製造方法。The method for producing a water-absorbent resin powder according to any one of claims 1 to 22, wherein an absorption capacity under load (1.96 kPa) of the obtained water-absorbent resin powder is 25 g / g or more. 粉砕後の吸水性樹脂粉末をさらに表面架橋する、請求項１０、１１、１６、１７および１８のいずれかに記載の吸水性樹脂粉末の製造方法。The method for producing a water absorbent resin powder according to any one of claims 10, 11, 16, 17, and 18, wherein the surface of the water absorbent resin powder after pulverization is further subjected to surface crosslinking. 含水ゲル状架橋重合体が、０〜９０モル％中和されたアクリル酸（塩）を主成分としアクリル酸（塩）以外のその他の単量体が０〜５０モル％である単量体を重合してなるものである、請求項１から２４までのいずれかに記載の吸水性樹脂粉末の製造方法。The hydrogel crosslinked polymer is a monomer having 0 to 90 mol% neutralized acrylic acid (salt) as a main component and other monomers other than acrylic acid (salt) being 0 to 50 mol%. The method for producing a water-absorbent resin powder according to any one of claims 1 to 24, which is obtained by polymerization.
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