JP4805490B2 - Method for producing water absorbent resin - Google Patents

Description

【０１１２】
に従ってＧＶ（無荷重下吸収倍率）を算出した。
【０１１３】
また、含水重合体のＧＶ測定では、固形分で０．２ｇを用い、生理食塩水への浸漬時間が２４時間、ＧＶ算出時に固形分補正を行う以外は、吸水性樹脂の場合と同様に行った。
【０１１４】
［可溶分量および中和率の測定］
２５０ｍｌ容量の蓋付きプラスチック容器に０．９重量％ＮａＣｌ水溶液（生理食塩水）の１８４．３ｇを測り取り、その水溶液中に吸水性樹脂１．００ｇを加え１６時間攪拌することにより樹脂中の可溶分量を抽出した。この抽出液を濾紙を用いて濾過することにより得られた濾液の５０．０ｇを測り取り測定溶液とした。
【０１１５】
はじめに生理食塩水だけを、まず、０．１ＮのＮａＯＨ水溶液でｐＨ１０まで滴定を行い、その後、０．１ＮのＨＣｌ水溶液でｐＨ２．７まで滴定して空滴定量（［ｂＮａＯＨ］ｍｌ、［ｂＨＣｌ］ｍｌ）を得た。
【０１１６】
同様の滴定操作を測定溶液についても行うことにより滴定量（［ＮａＯＨ］ｍｌ、［ＨＣｌ］ｍｌ）を求めた。
【０１１７】
例えばアクリル酸とそのナトリウム塩からなる吸水性樹脂の場合、その重量平均分子量と上記操作により得られた滴定量をもとに、吸水性樹脂中の可溶分量と中和率を以下の計算式により算出することができる。
【０１１８】
【数２】

【０１１９】
また、含水重合体の可溶分量測定では、固形分で１．００ｇを用い、生理食塩水への浸漬時間が２４時間、可溶分量算出時に固形分補正を行う以外は、吸水性樹脂の場合と同様に行った。
【０１２０】
［ＧＥＸ値］
ベースポリマーのＧＶ値をｙ（ｇ／ｇ），可溶分量をｘ（重量％）で表す時、ＧＥＸ値を次式で定義する。
【０１２１】
ＧＥＸ値＝（ｙ−１５）／ｌｎ（ｘ）
ｌｎ（ｘ）：ｘの自然対数
ＧＥＸ値は、ＧＶ値と可溶分量の関係において、ＧＶ値の割に可溶分量が少ないのを良いとし、多いのを劣るとする評価を、一つのパラメータで表すためのものであり、この値が大きいほど高性能である。
【０１２２】
［残存モノマーの測定］
脱イオン水１０００ｇに吸水性樹脂０．５ｇを加え、攪拌下で２時間抽出した後、膨潤ゲル化した吸水性樹脂を濾紙を用いて濾別し、濾液中の残存モノマー量を液体クロマトグラフィーで分析した。一方、既知濃度のモノマー標準溶液を同様に分析して得た検量線を外部標準とし、濾液の希釈倍率を考慮して、吸水性樹脂中の残存モノマー量を求めた。
【０１２３】
また、含水重合体の残存モノマー測定では、固形分で０．５ｇを用い、脱イオン水への浸漬時間が２４時間、残存モノマー算出時に固形分補正を行う以外は、吸水性樹脂の場合と同様に行った。
【０１２４】
［含水重合体の固形分濃度の測定］
重合器から取り出された含水重合体の一部を小量切り取って素早く冷やし、はさみで素早く細分化した含水重合体５ｇをシャーレにとり、１８０℃乾燥器中で２４時間乾燥して算出した。粒子状含水重合体の固形分濃度は、サンプル５ｇをシャーレにとり、１８０℃乾燥器中で２４時間乾燥して算出した。
【０１２５】
［濃縮比の算出］
重合により生成する含水重合体の固形分濃度と単量体水溶液中の固形分濃度との比（濃縮比）である。ここで、単量体水溶液中の固形分とは、単量体およびその他の添加剤であり、水や溶剤は含まない。例えば、単量体水溶液中の固形分濃度が４０重量％で、生成する含水重合体の固形分濃度が４８重量％の場合、濃縮比＝４８／４０＝１．２０となる。
【０１２６】
［加圧下の吸収倍率（ＡＡＰ）の測定］
ステンレス４００メッシュの金網（目の大きさ３８μｍ）を底に融着させた内径６０ｍｍのプラスチックの支持円筒の底の網上に、吸水性樹脂０．９ｇを均一に散布し、その上に吸水性樹脂に対して、２０ｇ／ｃｍ²（１．９６ｋＰａに相当）の荷重を均一に加えることができるように総重量が５６５ｇに調整された、外径が６０ｍｍよりわずかに小さく支持円筒の壁面との間に隙間が生じず、かつ上下の動きは妨げられないピストンと荷重をこの順に載置し、この測定装置一式の重量を測定する（Ｗａ）。
【０１２７】
直径１５０ｍｍのペトリ皿の内側に直径９０ｍｍのガラスフィルターを置き、０．９重量％ＮａＣｌ水溶液をガラスフィルターの表面と同レベルになるように加える。その上に直径９０ｍｍの濾紙を載せ表面が全て濡れるようにし、かつ過剰の液を除く。
【０１２８】
上記測定装置一式を上記湿った濾紙上に載せ、液を荷重下で吸収させる。１時間後測定装置一式を持ち上げ取り除き、その重量を再測定する（Ｗｂ）。
【０１２９】
加圧下の吸収倍率（ＡＡＰ）は、下記式：
【０１３０】
【数３】

【０１３１】
で求められる。
【０１３２】
［重合系の温度の測定］
温度変化の急速な系の測温のために、（株）キーエンス（Ｋｅｙｅｎｃｅ）製ＰＣカード型データ収集システムＮＲ−１０００を用い、熱伝対を重合系の中心部に置き、サンプリング周期０．１秒で測定した。得られた温度−時間チャートから重合開始温度、ピーク温度（最高到達温度）を読み取った。
【０１３３】
［重合時間］
単量体水溶液が重合容器に入れられ、重合開始条件が整った時（光分解型開始剤を用いる場合は、光照射開始時、光分解型開始剤を用いない場合は、単量体水溶液と重合開始剤が重合容器に入れられた時）から、ピーク温度までの時間を測定する。つまり、（誘導期間）＋（重合開始からピーク温度に達するまでの時間）を測定する。
【０１３４】
［重合昇温比］
重合昇温比とは、重合系で観察されたΔＴ（重合中の最高到達温度と重合開始温度との差、℃）と理論ΔＴ（℃）との比のことである。即ち、
重合昇温比＝（観察されたΔＴ（℃））／（理論ΔＴ（℃））
ここで、理論ΔＴ（℃）＝（単量体ｍｏｌ）×（１．８５ｋｃａｌ／ｍｏｌ）／（単量体水溶液中の固形分（ｋｇ）×０．５（ｋｃａｌ／℃／ｋｇ）＋単量体水溶液中の水（ｋｇ）×１．０（ｋｃａｌ／℃／ｋｇ））
［単量体水溶液の溶存酸素量の測定］
測定装置（セントラル科学（株）製ＤＯメーターＵＤ−１型）を用い、調製した単量体水溶液を窒素雰囲気中で、気泡をかみ込まないように穏やかに攪拌しながら、氷冷し、液温が５０℃の時の溶存酸素量を測定した。
【０１３５】
［中和率上昇］
ペースポリマーの中和率と単量体の中和率との差をポイントで表す。例えばペースポリマーの中和率が６５モル％で、単量体の中和率が６０モル％の場合、中和率上昇は５ポイントである。
【０１３６】
［重合中の膨張倍率の測定］
重合時に水が沸騰するため、重合系が膨張する場合がある。重合容器内に縦横にｃｍ刻みのスケールを付けておき、重合中に最も大きく膨張した時のサイズを目視で測り、その体積を求め、単量体水溶液の体積との比を算出する。即ち、
重合中の膨張倍率（倍）＝重合系の最大体積／単量体水溶液の体積
［粒子状含水重合体の粒度分布の測定］
約３００ｇの粒子状含水重合体をポリ袋に入れた後、アエロジルＲ−９７２（日本アエロジル（株）製、疎水性の微粒子状酸化珪素）１ｇを加え、手で混合し、良く解す（ほぐす）。解したものを、内径２０ｃｍの標準ふるいとＲｏ−Ｔａｐ式ふるい振とう器を用いて、１０分間振とうする。
【０１３７】
粒子状含水重合体の含水率によっては、ふるい振とう時に凝集して正確な粒度分布の測定が難しい場合があるために、アエロジルＲ−９７２を添加して再凝集を防ぎながら測定を行う。
【０１３８】
［可溶化試験法］
吸水性樹脂は、基本的に水溶性ポリマーが架橋された架橋体の形態を有している。この吸水性樹脂が、分解条件に暴露されたときの分解しやすさを見るための試験法が、この可溶化試験法である。従って、実際に暴露される分解条件によっては本試験法と必ずしも傾向が一致するとは限らない。
【０１３９】
本試験法では、水洗により、可溶分等を洗い流し、架橋体そのものからなるゲルを得て、これに紫外線を照射することにより分解させる。この評価方法により架橋体そのものの分解しやすさの定量的な指標が得られる。以下にその手順を示す。
１．吸水性樹脂を分級し、３００μｍ〜８５０μｍのものを分取する。
２．分取品０．５００ｇをＰＰ（ポリプロピレン）製の円筒状容器中の１０００ｃｃイオン交換水に分散・膨潤させる。この時、マグネチックスターラー（６００ｒｐｍ）で攪拌をしながら行う。
３．常温で、２時間攪拌を続ける。
４．この分散液を２０ｃｍ直径の円形の標準ふるい（目開き３００μｍ）にあける。ふるいを手でたたきながら水切りを行い、ふるい上に残るゲルを、再度ＰＰ製の円筒状容器中に戻し、イオン交換水を加えて全量を１０００ｃｃとし、再度攪拌を２時間行う。
５．この洗浄操作を３回行い、水切りをしたゲルを直径１５３ｍｍのガラスシャーレに入れる。
６．水銀ランプＨ４００ＢＬ（東芝ライテック（株）製）を反射笠ＳＮ−４０４２Ａ（東芝ライテック（株）製）に取り付け、水銀灯安定器Ｈ４Ｔ１Ｂ５１（岩崎電気（株）製）に接続・点灯させ、水銀ランプの下端から１８ｃｍ下の面にシャーレを置く。水銀ランプの真下１８ｃｍのところで照射エネルギーを紫外線積算光量計ＵＩＴ−１５０（ウシオ電気（株）製）を用いて測定すると４０ｍＷ／ｃｍ２である。
７．シャーレ上のゲルに水銀ランプで３０分間照射する。
８．照射後のシャーレ内容物をＰＰ製の円筒状容器中に戻し、イオン交換水を加えて全量を１０００ｃｃとし、攪拌を２時間行う。上記４，５と同様の操作を行うことで３回洗浄をする。
９．標準ふるい（目開き３００μｍ）上に残ったゲルを直径１５３ｍｍのガラスシャーレに入れ１８０℃の乾燥器で５時間乾固し、固形分量（ａ）を求める。
１０．別途、上記１〜５の操作を行って得られたゲル（ＵＶ照射前）について、その固形分量（ｂ）を上記９と同様にして求める。
１１．可溶化残存率は、可溶化残存率＝ａ／ｂ×１００（％）により算出される。
【０１４０】
−実施例１−
内径１０ｃｍのステンレスビーカーに窒素導入管、排気管、温度計を装備した発泡スチロール製のふたをつけ、さらにステンレスビーカー全体を断熱材である発泡スチロールで包んだ。ここにポリエチレングリコールジアクリレート（数平均分子量４７８）０．０９ｇを溶解した８０重量％アクリル酸水溶液４０．６ｇを入れ、マグネチックスターラーで攪拌しつつ、４８重量％苛性ソーダ水溶液２８．２ｇをイオン交換水３１．０ｇで希釈したものを添加し、中和した。内温は９０℃となった。この単量体水溶液の中和率は、７５モル％である。窒素を導入しながら、ここに過硫酸ソーダの１０重量％水溶液０．４５ｇを添加したところ、速やかに重合が始まり（重合開始温度９０℃）、水蒸気を発生しながら、重合ピーク温度（１０８℃）に達した。過硫酸ソーダ水溶液添加から重合ピーク温度までに要した時間、即ち重合時間は２分であった。重合ピーク温度を迎えた後も保温状態のまま５分間保持した後、含水重合体を取り出しはさみで細分化した。重合開始剤添加から含水重合体の取り出しまで、７分を要した。細分化した含水重合体を１７０℃熱風乾燥機で４０分間乾燥した後、卓上粉砕機で粉砕した。次いで粉砕物を目開き６００μｍと３００μｍの篩網で分級することにより、大部分が３００〜６００μｍの粒子径を持つベースポリマー（１）を得た。
【０１４１】
ベースポリマー（１）のＧＶは、４７ｇ／ｇ，可溶分量は１０重量％、残存モノマーは３００ｐｐｍ、中和率は７７モル％であった。また、細分化した含水重合体の固形分濃度は、４８重量％であった。濃縮比は１．２０であった。
次いで、ベースポリマー（１）１００部に対して、エチレングリコールジグリシジルエーテル０．０５部、プロピレングリコール１部、水２部からなる表面架橋剤組成液を混合し、得られた混合物を８０℃の乾燥機中で４０分間加熱処理することにより表面近傍が架橋された表面架橋吸水性樹脂（１）を得た。
【０１４２】
表面架橋吸水性樹脂（１）のＧＶは３９ｇ／ｇ、ＡＡＰは３８ｇ／ｇであった。
【０１４３】
結果を表１に示した。
【０１４４】
また、実施例１で得られた含水重合体の側面写真を図２に示す。図２の写真中央下にある横棒は、長さ１ｃｍである。
【０１４５】
−比較例１−
実施例１で用いたのと同じステンレスビーカーに、窒素導入管、排気管、温度計を装備した発泡スチロール製のふたをつけた重合装置を、２０℃の水浴に浸漬し、ここに、実施例１と同じ単量体水溶液を投入し、窒素を導入しつつ、過硫酸ソーダの１０重量％水溶液０．４５ｇおよび０．１重量％のＬ−アスコルビン酸水溶液０．４５ｇを添加した。７分後に重合が開始した。２０℃の水浴で冷却しながら重合したところ、ピーク温度は、６０℃に達した。その後、水浴を７０℃に切り替え、３０分加熱した。
【０１４６】
その後、含水重合体を取り出しはさみで細分化した。重合開始剤系の添加から含水重合体の取り出しまで、６２分を要した。細分化した含水重合体を１７０℃熱風乾燥機で４０分間乾燥した後、卓上粉砕機で粉砕した。次いで粉砕物を目開き６００μｍと３００μｍの篩網で分級することにより、大部分が３００〜６００μｍの粒子径を持つ比較ベースポリマー（１）を得た。
【０１４７】
比較ベースポリマー（１）のＧＶは３６ｇ／ｇ，可溶分量は１１重量％、残存モノマーは３００ｐｐｍ、中和率は７５モル％であった。また、細分化した含水重合体の固形分濃度は４２重量％であった。濃縮比は１．０５であった。
【０１４８】
次いで、比較ベースポリマー（１）１００部に対して、エチレングリコールジグリシジルエーテル０．０５部、プロピレングリコール１部、水２部からなる表面架橋剤組成液を混合し、得られた混合物を８０℃の乾燥機中で４０分間加熱処理することにより表面近傍が架橋された比較表面架橋吸水性樹脂（１）を得た。
【０１４９】
比較表面架橋吸水性樹脂（１）のＧＶは２８ｇ／ｇ、ＡＡＰは２６ｇ／ｇであった。
【０１５０】
結果を表１に示した。
【０１５１】
実施例１と比較例１は、単量体組成、開始剤量などは同一で、重合開始温度（実施例１では９０℃、比較例１では２０℃）とその後の温度が異なるだけの違いである。得られたベースポリマー、吸水性樹脂の性能は、実施例１のほうが優れている。この理由は明らかではないが、本発明者らの推測は次のようなものである。
【０１５２】
２０℃での重合開始では、重合率の低い段階で生成するポリマーが高分子量でありすぎることと、架橋剤が重合初期に多く消費されることから、ＧＶの低下につながっている（参考文献；Ｃｒｏｓｓｌｉｎｋｅｒ Ｒｅａｃｔｉｖｉｔｙ ａｎｄ ｔｈｅ Ｓｔｒｕｃｔｕｒｅ ｏｆ Ｓｕｐｅｒａｂｓｏｒｂｅｎｔ Ｇｅｌｓ，Ｄ．Ｊ．Ａｒｒｉｏｌａ ｅｔ ａｌ．，Ｊ．Ａｐｐｌ．Ｐｏｌｙｍ．Ｓｃｉ．６３，４３９−４５１（１９９７））のに対して、９０℃での重合開始では、重合率の低い段階で生成するポリマーの分子量が抑制されることから、ＧＶの低下が抑制されていると考えられる。
【０１５３】
−実施例２−
アクリル酸８３．５部、４８．５重量％ＮａＯＨ水溶液の６２．１部、イオン交換水５４．３部、架橋剤としてのポリエチレングリコールジアクリレート（エチレンオキシドの数平均重合度＝８）０．１１部、および開始剤として２−ヒドロキシ−２−メチル−１−フェニル−プロパン−１−オンの０．０１部を混合することにより単量体濃度５０重量％、中和率６５モル％の単量体水溶液を作成した。この溶液を窒素ガス雰囲気下で３０分間脱気した後、９０℃のホットプレート（ＮＥＯ ＨＯＴＰＬＡＴＥ ＨＩ−１０００（株）井内盛栄堂製）上に置かれ、窒素ガスを導入した底面２００×２６０ｍｍのテフロンコートしたステンレス製容器中に注いだ。単量体水溶液が６０℃まで昇温した時点で、ブラックライト蛍光ランプ（（株）東芝ライテック社製ＦＬ６ＢＬＢを４本）を用いて１０分間紫外線照射することにより（光量９００ｍＪ／ｃｍ²）、厚さ約３ｍｍの含水重合体を得た。重合開始温度は６０℃で、重合中の最高温度は１１０℃、重合時間は８０秒、膨張倍率は５倍であった。紫外線照射終了後、ただちに含水重合体を取り出し、はさみで細断し、１７０℃中で３０分間熱風乾燥を行い、卓上粉砕機で粉砕した。次いで粉砕物を目開き６００μｍと３００μｍの篩網で分級することにより、大部分が３００〜６００μｍの粒子径を持つベースポリマー（２）を得た。
【０１５４】
ベースポリマー（２）のＧＶは５８ｇ／ｇ、可溶分量は１６重量％、中和率は６８モル％、残存モノマーは２２００ｐｐｍであった。また、含水重合体の固形分濃度は６０重量％であり、濃縮比は１．２０であった。
【０１５５】
次いで、ベースポリマー（２）１００部に対して、エチレングリコールジグリシジルエーテル０．０５部、プロピレングリコール１部、水２部からなる表面架橋剤組成液を混合し、得られた混合物を８０℃の乾燥機中で４０分間加熱処理することにより表面近傍が架橋された表面架橋吸水性樹脂（２）を得た。
【０１５６】
表面架橋吸水性樹脂（２）のＧＶは４２（ｇ／ｇ）、ＡＡＰは３６（ｇ／ｇ）であった。
【０１５７】
結果を表１に示した。
【０１５８】
−実施例３−
アクリル酸１３９．５ｇ、ポリエチレングリコールジアクリレート（数平均分子量４７８）０．０９ｇ、および２−ヒドロキシ−２−メチル−１−フェニル−プロパン−１−オン０．０２ｇを混合した溶液（Ａ）、４８．５重量％ＮａＯＨ水溶液９５．８ｇをイオン交換水６１．２ｇで希釈し、さらにジエチレントリアミン５酢酸・五ナトリウム０．０２ｇを加えたＮａＯＨ水溶液（Ｂ）をそれぞれ調製整し、窒素ガス雰囲気下で３０分間脱気した。マグネチックスターラーで攪拌しながら（Ｂ）に（Ａ）を開放系で一気に加え混合した。混合初期に析出物が見られるがすぐに溶解し、中和熱と溶解熱で液温が約９０℃まで上昇した単量体水溶液（単量体濃度５５重量％、中和率６０モル％）が得られた。さらに、この単量体水溶液に１０重量％過硫酸ナトリウム水溶液０．５８ｇを加え数秒攪拌した後すぐに、９０℃ホットプレート上に置かれ、内面にシリコンシートを貼りつけた底面２００×２６０ｍｍのステンレス製バット型容器（表面温度約６４℃）中に開放系で注いだ（溶液の厚さ約５ｍｍ）。ステンレス製バット型容器は、そのサイズが底面２００×２６０ｍｍ、上面５６０×４６０ｍｍ、高さ１４０ｍｍであり、中心断面が台形で、上面が開放されている。そしてすぐにブラックライト水銀ランプ（ピーク波長３５２ｎｍ、形式Ｈ４００ＢＬ、投光器ＭＴ−４０２０内に装着、ランプ・投光器ともに（株）東芝ライテック社製）で紫外線照射を行い重合を開始させた。水蒸気を発生し上下左右に膨張発泡しながら重合は進行し、その後もとのサイズと同程度に収縮した。目視で推定したところ最大で単量体水溶液の体積の約３０倍に含水重合体は膨張した後収縮していた。含水重合体の膨張時には、薄い含水重合体が容器の側面の傾斜部分を這い上がり、収縮時には、元の方向に戻るが底面サイズよりも大きな含水重合体となって動きが止まる。この膨張収縮は約１分以内に終了し、２分間ＵＶ照射を行った時点で含水重合体を取り出した。重合系の温度変化の記録から、重合開始温度は８８℃で最高到達温度は１１１℃であることが読み取られた。得られた含水重合体は、気泡のサイズにもよるがそのままかつぶれた状態となって皺の多い形態であった。この含水重合体を竪型粉砕機（形式ＶＭ２７−Ｓ、（株）オリエント社製、スクリーン径８ｍｍ）で粉砕して流動性のある粒子状の含水重合体（３）を得た。
【０１５９】
含水重合体（３）のＧＶは３３ｇ／ｇ、可溶分量は６重量％、残存モノマーは６００ｐｐｍ、また固形分濃度は７０重量％であり、濃縮比は１．２７であった。
【０１６０】
続いて含水重合体（３）を１７０℃中で２０分間熱風乾燥を行い、乾燥物をロールミルを用いて粉砕した。次いで粉砕物を目開き８５０μｍと１５０μｍの篩網で分級することにより、大部分が１５０〜８５０μｍの粒子径を持ち重量平均粒子径が３６０μｍのベースポリマー（３）を得た。
【０１６１】
ベースポリマー（３）のＧＶは４８（ｇ／ｇ）、可溶分量は２４重量％、中和率は６５モル％、残存モノマーは２００ｐｐｍであった。またベースポリマー（３）の粒子を顕微鏡にて観察したところ、重合が発泡を伴っていたにもかかわらずその気泡サイズが比較的大きいためか、大部分の粒子は気泡を含まない非晶質状となっていた。
【０１６２】
次いで、ベースポリマー（３）１００部に対して、エチレングリコールジグリシジルエーテル０．０３部、プロピレングリコール１部、水５部からなる表面架橋剤組成液を混合し、得られた混合物を密閉容器中で８０℃の乾燥機内で１時間加熱処理することにより表面近傍が架橋された表面架橋吸水性樹脂（３）を得た。
表面架橋吸水性樹脂（３）のＧＶは３４ｇ／ｇ、ＡＡＰは３５ｇ／ｇであった。
さらに、ベースポリマー（３）１００部に対して、エチレングリコールジグリシジルエーテル０．０３部、プロピレングリコール１部、水３部、イソプロピルアルコール０．９部からなる表面架橋剤組成液を混合し、得られた混合物を１７０℃のオイルバスで加熱された容器中で２０分間加熱処理することにより表面近傍が架橋された表面架橋吸水性樹脂（３ａ）を得た。
【０１６３】
表面架橋吸水性樹脂（３ａ）のＧＶは３４ｇ／ｇ、ＡＡＰは３５ｇ／ｇであった。
【０１６４】
結果を表１に示した。
【０１６５】
また、実施例３で得られた含水重合体の側面写真を図３に、上面写真を図４に、下面写真を図５に示す。図３、図４および図５の写真中央下にある横棒は、長さ１ｃｍである。
【０１６６】
−実施例４−
実施例３と同様に重合を行い、蒸発水蒸気をファンを用いて氷水で冷却したコンデンサーに導き、捕集した。この操作を２回行い捕集された水溶液は６０ｇで、そのうちアクリル酸が３．４重量％含まれていた。
【０１６７】
このアクリル酸を含む回収水を、実施例３のイオン交換水の大半と置き換えて使用した以外は実施例３と同じ操作を行った。得られたベースポリマー（４）の物性値を表１に示した。
【０１６８】
−実施例５−
実施例３で、架橋剤ポリエチレングリコールジアクリレート（数平均分子量４７８）０．０９ｇに換えて、トリメチロールプロパントリアクリレート（分子量２９６）０．１４ｇを用いた以外は、実施例３と同様に行い、ベースポリマー（５）を得た。得られたベースポリマー（５）１００部に、プロピレングリコール１部、１，４ブタンジオール０．５部、水３部、イソプロピルアルコール１部とからなる表面架橋剤組成液を混合した。上記混合物を２１０℃で４０分間加熱処理することにより表面架橋吸水性樹脂（５）を得た。
【０１６９】
結果を表１に示した。
【０１７０】
また、実施例５で得られた含水重合体の側面写真を図６に示す。図６の写真中央下にある横棒は、長さ１ｃｍである。
【０１７１】
−実施例６−
実施例５で得られたベースポリマー（５）１００部に、エチレンカーボネート３部、水３部、イソプロピルアルコール１部とからなる表面架橋剤組成液を混合した。上記混合物を２１０℃で４０分間加熱処理することにより表面架橋吸水性樹脂（６）を得た。
【０１７２】
結果を表１に示した。
【０１７３】
【表１】

【０１７４】
−実施例７〜１０−
単量体水溶液の温度とホットプレート温度を調整することで重合開始温度を変化させた以外は、実施例３と同様に重合およびその後の操作を行い、実施例７〜１０のベースポリマー（ベースポリマー（７）〜（１０））をそれぞれ得た。結果を表２にまとめた。
【０１７５】
また、実施例７で得られた含水重合体の側面写真を図７に示す。また、実施例７の含水重合体の一部を切り取り、水道水で膨潤させたゲルの写真を図８に示す。図８の写真で、シャーレの外にある含水重合体は、水道水で膨潤させる前の含水重合体の切り取り切片と同様の切片である。図７および８の写真左下にある縦棒は、長さ１ｃｍである。
【０１７６】
【表２】

【０１７７】
また、実施例３および実施例７〜１０のベースポリマーについて、重合反応温度と時間との関係を表したグラフを図１に示した。
【０１７８】
実施例７〜１０は、同一単量体組成で、単に重合開始温度を８８℃、７３℃、６０℃、４４℃と変化させたものである。開始温度が高いほど、ペースポリマーの性能が良く、含水重合体の固形分濃度も高くなっている。また、ピーク温度は、開始温度が高い程低い。こうした現象の理由は明らかではないが、本発明者らの推測は次のようなものである。
【０１７９】
重合開始温度が低いと開始から沸騰に達するまでに硬い含水重合体が生成するため、沸騰温度が高くなり、つまりピーク温度も高くなり、破裂音も大きい。重合開始温度が高いと開始から沸騰に達するまでに硬い含水重合体が生成せず、粘度の高い単量体水溶液が沸騰とともに大きく発泡して表面積が大きくなり、水蒸気が良く揮散し、ピーク温度が抑えられ固形分濃度も高くなる。破裂音もほとんどない。
【０１８０】
−比較例２−
アクリル酸７２．１ｇをイオン交換水２２．２ｇに加え、更にこれに中和剤として純度８５％の水酸化カリウム４９．５ｇと、ジビニル系化合物としてＮ，Ｎ’−メチレンビスアクリルアミド０．０１ｇとを順次添加し、混合単量体濃度７０重量％のアクリル酸カリウム溶液（中和率７５モル％）を調製した。
【０１８１】
上記で調製された水溶液を７０℃に保温し、これに過硫酸アンモニウムの１８重量％水溶液２．９ｇ（アクリル酸カリウム、遊離アクリル酸及びＮ，Ｎ’−メチレンビスアクリルアミドの合計重量（単量体成分合計重量）に対し０．５重量％）及び亜硫酸水素ナトリウムの３０．６重量％水溶液１．７ｇ（０．５重量％）を混合し、混合液をステンレス製ビーカー（容量２Ｌ、φ１３５ｍｍ）に投入すると厚さ約１０ｍｍの層状になった。約７秒後、重合反応が開始され、該反応は約１分間で完結しその間の最高温度は１４５℃であった。
得られた含水重合体は固体状で、容易に粉砕できるものであり、比較ベースポリマー（２）を得た。その固形分濃度は８９重量％、ＧＶは２３ｇ／ｇ、可溶分量は５０重量％、中和率は７７モル％、残存モノマーは５９００ｐｐｍであった。
【０１８２】
結果を表２にまとめた。
【０１８３】
本比較例は、特開昭５８−７１９０７（荒川化学）の実施例１をトレースしたものである。固形分濃度が８９重量％までになると、可溶分量が著しく増加することがわかる。
【０１８４】
−実施例１１−
アクリル酸１３９．５ｇ、ポリエチレングリコールジアクリレート（数平均分子量４７８）０．０９ｇ、および２−ヒドロキシ−２−メチル−１−フェニル−プロパン−１−オン０．０２ｇを混合した溶液（Ａ）、４８．５重量％ＮａＯＨ水溶液９５．８ｇをイオン交換水６４．１ｇで希釈し、さらにジエチレントリアミン５酢酸・５ナトリウム０．０２ｇを加えたＮａＯＨ水溶液（Ｂ）をそれぞれ調整し、窒素ガス雰囲気下で３０分間脱気した。マグネチックスターラーで攪拌しながら（Ｂ）に（Ａ）を開放系で一気に加え混合した。混合初期に析出物が見られるがすぐに溶解し、中和熱と溶解熱で液温が約８５℃まで上昇した単量体水溶液（単量体濃度５５重量％、中和率６０モル％）が得られた。さらに、この単量体水溶液に１０重量％過硫酸ナトリウム水溶液０．５８ｇを加え数秒攪拌した後すぐに、９０℃ホットプレート上に置かれ、内面にシリコンシートを貼りつけた底面２００×２６０ｍｍのステンレス製バット型容器（表面温度約６４℃）中に開放系で注いだ（溶液の厚さ約５ｍｍ）。ステンレス製バット型容器は、そのサイズが底面２００×２６０ｍｍ、上面５６０×４６０ｍｍ、高さ１４０ｍｍであり、中心断面が台形で、上面が開放されている。そしてすぐにブラックライト水銀ランプ（ピーク波長３５２ｎｍ、形式Ｈ４００ＢＬ、（株）東芝ライテック社製）でＵＶ照射を行い重合を開始させた。水蒸気を発生し上下左右に膨張発泡しながら重合は進行し、その後もとのサイズと同程度に収縮した。目視で推定したところ最大で単量体水溶液の体積の約３０倍に含水重合体は膨張した後収縮していた。含水重合体の膨張時には、薄い含水重合体が容器の側面の傾斜部分を這い上がり、収縮時には、元の方向に戻るが底面サイズよりも大きな含水重合体となって動きが止まる。この膨張収縮は約１分以内に終了し、２分間ＵＶ照射を行った時点で含水重合体を取り出した。なお、温度計測チャートより重合開始温度は８２℃、最高到達温度は１１３℃が読み取られた。得られた含水重合体（１１）は、皺の多い形態であり、固形分濃度は７０重量％であった。従って濃縮比は１．２７であった。この含水重合体（１１）を竪型粉砕機（形式ＶＭ２７−Ｓ、スクリーン径３ｍｍ、（株）オリエント社製）で粉砕して流動性のある粒子状含水重合体（１１）を得た。
【０１８５】
粒子状含水重合体（１１）の重量平均粒径は１ｍｍ、ＧＶは３３ｇ／ｇ、可溶分量は６重量％、残存モノマーは６００ｐｐｍ、固形分濃度は７１重量％であった。
【０１８６】
続いて粒子状含水重合体（１１）を１７０℃の乾燥器中で２０分間熱風乾燥を行い、乾燥物をロールミルを用いて粉砕した。次いで粉砕物を目開き８５０μｍと１５０μｍの篩網で分級することにより、大部分が１５０〜８５０μｍの粒子径を持ち重量平均粒子径が３６０μｍのベースポリマー（１１）を得た。
【０１８７】
ベースポリマー（１１）のＧＶは４８ｇ／ｇ、可溶分量は２４重量％、中和率は６５モル％、残存モノマーは２００ｐｐｍであった。またベースポリマー（１１）の粒子を顕微鏡にて観察したところ、重合が発泡を伴っていたにもかかわらずその気泡サイズが比較的大きいためか、大部分の粒子は気泡を含まない非晶質状となっていた。
【０１８８】
次いで、ベースポリマー（１１）１００部に対して、エチレングリコールジグリシジルエーテル０．０３部、プロピレングリコール１部、水５部からなる表面架橋剤組成液を混合し、得られた混合物を密閉容器中で８０℃の乾燥機内で１時間加熱処理することにより表面近傍が架橋された表面架橋吸水性樹脂（１１）を得た。
【０１８９】
表面架橋吸水性樹脂（１１）のＧＶは３４ｇ／ｇ、ＡＡＰは３２ｇ／ｇであった。
【０１９０】
さらに、ベースポリマー（１１）１００部に対して、エチレングリコールジグリシジルエーテル０．０３部、プロピレングリコール１部、水３部、イソプロピルアルコール０．９部からなる表面架橋剤組成液を混合し、得られた混合物を１７０℃のオイルバスで加熱された容器中で２０分間加熱処理することにより表面近傍が架橋された表面架橋吸水性樹脂（１１ａ）を得た。
【０１９１】
表面架橋吸水性樹脂（１１ａ）のＧＶは３４ｇ／ｇ、ＡＡＰは３５ｇ／ｇであった。
【０１９２】
−実施例１２−
アクリル酸３０８．２ｇ、ポリエチレングリコールジアクリレート（数平均分子量４７８）０．２０ｇ、および２−ヒドロキシ−２−メチル−１−フェニル−プロパン−１−オン０．０４ｇを混合した溶液（Ａ）、４８．５重量％ＮａＯＨ水溶液１９４．１ｇをイオン交換水９７．０ｇで希釈したＮａＯＨ水溶液（Ｂ）をそれぞれ調製し、マグネチックスターラーで攪拌しながら（Ｂ）に（Ａ）を開放系で一気に加え混合した。混合初期に析出物が見られるがすぐに溶解し、単量体水溶液（単量体濃度６０重量％、中和率５５モル％、温度１０２℃）が得られた。（この単量体水溶液調製作業を別バッチで同様に行い、溶存酸素量を測定したところ、０．７ｐｐｍであった。）さらに、この単量体水溶液に１０重量％過硫酸ナトリウム水溶液１．３ｇを加え数秒攪拌した後すぐに、９０℃ホットプレート上に置かれ、内面にシリコンシートを貼りつけたステンレス製バット型容器中に開放系で注いだ。ステンレス製バット型容器は、そのサイズが底面２００×２６０ｍｍ、上面５６０×４６０ｍｍ、高さ１４０ｍｍであり、中心断面が台形で、上面が開放されている。そしてすぐにブラックライト水銀ランプ（ピーク波長３５２ｎｍ、形式Ｈ４００ＢＬ、（株）東芝ライテック社製）でＵＶ照射を行い重合を開始させた。水蒸気を発生し上下左右に膨張発泡しながら重合は進行し（膨張倍率は４０倍）、２分間ＵＶ照射を行った時点で含水重合体を取り出した。この含水重合体の固形分濃度は７７重量％であった。この含水重合体を竪型粉砕機（形式ＶＭ２７−Ｓ、スクリーン径３ｍｍ、（株）オリエント社製）で、孔径１ｍｍのスクリーンを用いて粉砕することにより流動性のある粒子状含水重合体を得た。この粒子状含水重合体を続いて、目開き８５０μｍと１５０μｍの篩で分級して、重量平均粒径が５００μｍの粒子状含水重合体（１２）を得た。
【０１９３】
粒子状含水重合体（１２）のＧＶは２２ｇ／ｇ、可溶分量は２重量％、残存モノマーは６００ｐｐｍ、固形分濃度は７９重量％である。
【０１９４】
−実施例１３−
アクリル酸２７９．０ｇ、ポリエチレングリコールジアクリレート（数平均分子量４７８）０．０９ｇ、および２−ヒドロキシ−２−メチル−１−フェニル−プロパン−１−オン０．０３ｇを混合した溶液（Ａ）、４８．５重量％ＮａＯＨ水溶液１９１．５４ｇをイオン交換水１２８．２ｇで希釈したＮａＯＨ水溶液（Ｂ）をそれぞれ調製した。マグネチックスターラーで攪拌しながら（Ｂ）に（Ａ）を開放系で一気に加え混合した。混合初期に析出物が見られるがすぐに溶解し、単量体水溶液（単量体濃度５５重量％、中和率６０モル％、温度９２℃）が得られた。（この単量体水溶液調整作業を別バッチで同様に行い、溶存酸素量を測定したところ、１．４ｐｐｍであった。）さらに、この単量体水溶液に１０重量％過硫酸ナトリウム水溶液１．３ｇを加え数秒攪拌した後すぐに、９０℃ホットプレート上に置かれ、内面にシリコンシートを貼りつけたステンレス製バット型容器中に開放系で注いだ。ステンレス製バット型容器は、そのサイズが底面２００×２６０ｍｍ、上面５６０×４６０ｍｍ、高さ１４０ｍｍであり、中心断面が台形で、上面が開放されている。そしてすぐにブラックライト水銀ランプ（ピーク波長３５２ｎｍ、形式Ｈ４００ＢＬ、（株）東芝ライテック社製）でＵＶ照射を行い、重合を開始させた。水蒸気を発生し上下左右に膨張発泡しながら重合は進行し（膨張倍率は３５倍）、２分間ＵＶ照射を行った時点で含水重合体を取り出した（固形分濃度は６９重量％）。この含水重合体を竪型粉砕機（形式ＶＭ２７−Ｓ、（株）オリエント社製）で、初めに孔径３ｍｍのスクリーンを用い粉砕してから、さらにその粉砕物を孔径１ｍｍのスクリーンを用いて粉砕することにより流動性のある粒子状含水重合体を得た。この粒子状含水重合体を続いて、目開き８５０μｍと１５０μｍの篩で分級して、重量平均粒径が６１０μｍの粒子状含水重合体（１３）を得た（固形分濃度は７０重量％）。
【０１９５】
粒子状含水重合体（１３）のＧＶは３４ｇ／ｇ、可溶分量は１０重量％、残存モノマーは７００ｐｐｍであった。
【０１９６】
ついで、粒子状含水重合体（１３）１００部に対して、エチレングリコールジグリシジルエーテル０．０２部、プロピレングリコール０．２部からなる表面架橋剤組成液を混合し、得られた混合物を密閉容器中で８０℃の乾燥機内で１時間加熱処理を行った。加熱後の粒子は一旦、凝集塊となるものの、室温まで冷却することにより容易に粒子状に解砕することができ、表面近傍が架橋された表面架橋吸水性樹脂（１３）を得た。
【０１９７】
表面架橋吸水性樹脂（１３）のＧＶは２５ｇ／ｇ、ＡＡＰは２３ｇ／ｇ、残存モノマーは２００ｐｐｍ、固形分濃度は７４重量％である。
【０１９８】
−実施例１４−
実施例１１で得られた、皺の多い形態の含水重合体（１１）１枚を丸鋸で大略四つ切りにした後、スクリーン径３ｍｍのターボカッター（Ｃ−３００、ターボ工業（株）製）に投入し解砕して、粒子状含水重合体（１４）を得た。３０分間で約５０ｋｇの含水重合体（１１）を処理できた。
【０１９９】
得られた粒子状含水重合体（１４）の固形分濃度は７１重量％、重量平均粒径は１．３ｍｍであった。Ｒｏ−Ｔａｐ式ふるい振とう器で求めた粒度分布は次に示すとおりであった。
粒径２ｍｍ以上の粒子状含水重合体 ９重量％
粒径１．４ｍｍ以上２ｍｍ未満の粒子状含水重合体 ３８重量％
粒径１ｍｍ以上１．４ｍｍ未満の粒子状含水重合体 ３１重量％
粒径０．５ｍｍ以上１ｍｍ未満の粒子状含水重合体 １９重量％
粒径０．５ｍｍ未満の粒子状含水重合体 ３重量％
−実施例１５−
実施例１４のターボカッターで解砕して得られた粒子状含水重合体（１４）をターボグラインダー（ＴＧ−３００ 、ターボ工業（株）製）に投入しさらに解砕して、粒子状含水重合体（１５）を得た。
ターボグラインダーのスクリーン径、解砕後の粒子状含水重合体（１５）の重量平均粒径および固形分濃度を表４に示した。
【０２００】
−実施例１６−
粒子状含水重合体（１４）および（１５）を流動層乾燥器（Ｐｕｌｖｉｓ ＧＢ２２，ヤマト科学（株）製）を用いて、内温；１８０℃、材料１００グラム、熱風流速；０．３５立方メートル／分の条件で乾燥した。
【０２０１】
下表に、乾燥中の粒子状含水重合体（１４）および（１５）の材料温度、乾燥後の固形分濃度、乾燥物を粉砕後に、３００μｍ〜６００μｍを分級して得られた乾燥粒子状重合体（１４）および（１５）の、ＧＶ、可溶分量、残存モノマーを測定した値を表３に示す。
【０２０２】
【表３】

【０２０３】
−実施例１７−
実施例１１で得られた皺の多い形態の含水重合体（１１）１枚を丸鋸で大略四つ切りにした後、スクリーン径２ｍｍのロートプレックス（２８／４０Ｒｏ，ホソカワミクロン（株）製）に連続的に投入した。処理量は約７０ｋｇ／時であった。
【０２０４】
解砕後、サイクロンで捕集して得られた粒子状含水重合体（１７）の固形分濃度は７２重量％、重量平均粒径は約１ｍｍであった。粒子状含水重合体（１７）のＲｏ−Ｔａｐ式ふるい振とう器で求めた粒度分布は次に示すとおりであった。
粒径２ｍｍ以上の粒子状含水重合体 １重量％
粒径１．２ｍｍ以上２ｍｍ未満の粒子状含水重合体 ２９重量％
粒径０．８５ｍｍ以上１．２ｍｍ未満の粒子状含水重合体 ３５重量％
粒径０．３ｍｍ以上０．８５ｍｍ未満の粒子状含水重合体 ２６重量％
粒径０．３ｍｍ未満の粒子状含水重合体 ９重量％
−実施例１８−
実施例１１で得られた皺の多い形態の含水重合体（１１）１枚を丸鋸で大略四つ切りにした後、スクリーン径５ｍｍのロートプレックス（２８／４０Ｒｏ，ホソカワミクロン（株）製）に連続的に投入した。処理量は約１００ｋｇ／時 であった。
【０２０５】
解砕後、サイクロンで捕集して得られた粒子状含水重合体（１８）の固形分濃度は７１重量％、重量平均粒径は２ｍｍであった。粒子状含水重合体（１８）のＲｏ−Ｔａｐ式ふるい振とう器で求めた粒度分布は次に示すとおりであった。
粒径２．８ｍｍ以上の粒子状含水重合体 ６重量％
粒径１．７ｍｍ以上２．８ｍｍ未満の粒子状含水重合体 ５８重量％
粒径０．８５ｍｍ以上１．７ｍｍ未満の粒子状含水重合体 ２９重量％
粒径０．１５ｍｍ以上０．８５ｍｍ未満の粒子状含水重合体 ６重量％
粒径０．１５ｍｍ未満の粒子状含水重合体 １重量％
次に、この解砕された粒子状含水重合体（１８）をドライマイスタ（ホソカワミクロン（株）製、熱風と分散ローターにより粉砕と乾燥を同時に行う装置）に投入した。この時、熱風温度は２７０℃、分散ローターは３０００ｒｐｍであった。
【０２０６】
乾燥され、サイクロンで捕集された粒子状含水重合体（１８ａ）のＲｏ−Ｔａｐ式ふるい振とう器で求めた粒度分布は次に示すとおりであった。
粒径２．８ｍｍ以上の粒子状含水重合体 １重量％
粒径１．７ｍｍ以上２．８ｍｍ未満の粒子状含水重合体 ５重量％
粒径０．８５ｍｍ以上１．７ｍｍ未満の粒子状含水重合体 ２４重量％
粒径０．１５ｍｍ以上０．８５ｍｍ未満の粒子状含水重合体 ５９重量％
粒径０．１５ｍｍ未満の粒子状含水重合体 １１重量％
粒子状含水重合体（１８ａ）の固形分濃度は９４重量％、重量平均粒子径０．４ｍｍであった。運転後のドライマイスタ内部には付着物は全くみられなかった。
【０２０７】
この乾燥・粉砕された粒子状含水重合体（１８ａ）のＧＶは４０ｇ／ｇ、可溶分量は１５重量％、残存モノマーは４００ｐｐｍであった。
【０２０８】
−実施例１９−
実施例１１で得られた皺の多い形態の含水重合体（１１）１枚を丸鋸で大略四つ切りにした後、卓上両用型粉砕機（ＦＤＳ型（株）みやこ物産、スクリーン径１ｍｍ、ハンマークラッシャータイプの粉砕機）に投入したが、直ぐに詰まってしまい、排出されなかった。そこで、排出口に集塵機（（株）マキタ製 乾湿両用 業務用 モデル４０６）を接続し、粉砕機内に空気流を作るようにしたところスムースに排出されるようになった。排出物の固形分濃度は７８重量％、重量平均粒径６５０μｍで、その内、粒径が１５０μｍ以下のものは７重量％であった。
【０２０９】
粉砕時に通気することによって、粉砕時の発熱により発生した水分をすばやく持ち去り、材料の粘着性を低減できたために粉砕が可能となったと考えられる。
【０２１０】
−実施例２０−
実施例１１で得られた皺の多い形態の含水重合体（１１）１枚を丸鋸で大略四つ切りにした後、カッターミル（（株）ホーライ製、ＵＧ０３−２８０ＬＦＴ、スクリーン径８ｍｍ）に投入した。なお、このカッターミルには送風機（ＤＦ型ファン、ＤＦ−３、送風量１５ｍ³／ｍｉｎ、（株）ホーライ製）およびサイクロンが接続されており、解砕されたものはサイクロン下部より得られる。解砕して得られた粒子状含水重合体（２０）の固形分濃度は７２重量％、重量平均粒径は３ｍｍであった。この粒子状含水重合体（２０）のＲｏ−Ｔａｐ式ふるい振とう器で求めた粒度分布は次に示すとおりであった。
粒径４ｍｍ以上の粒子状含水重合体 １７重量％
粒径２ｍｍ以上４ｍｍ未満の粒子状含水重合体 ６９重量％
粒径１ｍｍ以上２ｍｍ未満の粒子状含水重合体 １３重量％
粒径１ｍｍ未満の粒子状含水重合体 １重量％
次に、この粒子状含水重合体（２０）をメッシュミル（（株）ホーライ製、ＨＡ８−２５４２、スクリーン径２ｍｍ）に投入しさらに解砕した。サイクロンで捕集された粒子状含水重合体（２０ａ）の固形分濃度は７５重量％、重量平均粒径は０．６ｍｍであった。処理量は時間当たり１３０ｋｇであった。この粒子状含水重合体（２０ａ）のＲｏ−Ｔａｐ式ふるい振とう器で求めた粒度分布は次に示すとおりであった。
粒径１．４ｍｍ以上の粒子状含水重合体 ０重量％
粒径１ｍｍ以上１．４ｍｍ未満の粒子状含水重合体 ８重量％
粒径０．８５ｍｍ以上１ｍｍ未満の粒子状含水重合体 １７重量％
粒径０．１５ｍｍ以上０．８５ｍｍ未満の粒子状含水重合体 ７２重量％
粒径０．１５ｍｍ未満の粒子状含水重合体 ３重量％
運転後のメッシュミル内部には付着物は全くみられなかった。
【０２１１】
−実施例２１−
アクリル酸８３．５部、４８．５重量％ＮａＯＨ水溶液の６２．１部、イオン交換水５４．３部、架橋剤としてのポリエチレングリコールジアクリレート（エチレンオキシドの数平均重合度＝８）０．１１部、および開始剤として２−ヒドロキシ−２−メチル−１−フェニル−プロパン−１−オンの０．０１部を混合することにより単量体濃度５０重量％、中和率６５ｍｏｌ％、温度８６℃の単量体水溶液を作成した（この単量体水溶液調製作業を別バッチで同様に行ない、溶存酸素量を測定したところ、３．０ｐｐｍであった）。この単量体水溶液を９０℃のホットプレート上に置かれ、窒素ガスを導入した底面２００×２６０ｍｍのテフロンコートしたステンレス製容器中に注いだ。単量体水溶液が８０℃になった時点で、ブラックライト蛍光ランプを用いて１０分間紫外線照射することにより（光量７８０ｍＪ／ｃｍ²）、厚さ約３ｍｍの含水重合体（２１）を得た。固形分濃度は６０重量％であった。従って濃縮比は１．２０であった。この重合中の最高温度は１１０℃であった。含水重合体（２１）を竪型粉砕機（形式ＶＭ２７−Ｓ、スクリーン径３ｍｍ、（株）オリエント社製）で細断し、重量平均粒径１．６ｍｍ、固形分濃度６１重量％の粒子状含水重合体（２１）を得た。この粒子状含水重合体（２１）を１７０℃中で３０分間熱風乾燥を行い、卓上粉砕機で粉砕した。次いで粉砕物を目開き６００μｍと３００μｍの篩網で分級することにより、大部分が３００〜６００μｍの粒子径を持つベースポリマー（２１）を得た。
【０２１２】
ベースポリマー（２１）のＧＶは５８ｇ／ｇ、可溶分量は１６重量％、中和率は６８モル％、残存モノマーは２２００ｐｐｍであった。
【０２１３】
次いで、ベースポリマー（２１）１００部に対して、エチレングリコールジグリシジルエーテル０．０５部、プロピレングリコール１部、水２部からなる表面架橋剤組成液を混合し、得られた混合物を８０℃の乾燥機中で４０分間加熱処理することにより表面近傍が架橋された表面架橋吸水性樹脂（２１）を得た。
【０２１４】
表面架橋吸水性樹脂（２１）のＧＶは４２ｇ／ｇ、ＡＡＰは３６ｇ／ｇであった。
実施例１１〜１５、および１７〜２１の含水重合体の解砕について表４にまとめた。
【０２１５】
【表４】

【０２１６】
−比較例３−
実施例１１で得られた皺の多い形態の含水重合体（１１）１枚を丸鋸で大略四つ切りにした後、孔径８ｍｍのダイスを有するミートチョッパー（平賀製作所製）に投入したところ、負荷が大きすぎて直ちに停止し、解砕されなかった。
【０２１７】
−比較例４−
実施例１１で得られた皺の多い形態の含水重合体（１１）１枚を丸鋸で大略四つ切りにした後、スクリーン径３ｍｍのサンプルミル（ＫIIＷ−１型、不二パウダル（株）製）に投入したところ、負荷が大きすぎて直ちに停止し、解砕されなかった。
【０２１８】
−比較例５−
実施例１１で得られた皺の多い形態の含水重合体（１１）１枚を、シグマ型翼を有するニーダー（２．５Ｌ内容積、小池鉄工（株）製）に投入したところ、練られるが、解砕はされなかった。
【０２１９】
−比較例６−
実施例１１で得られた皺の多い形態の含水重合体（１１）１枚を丸鋸で大略四つ切りにした後、特開平１１−１８８７２７の図４の装置に投入したところ、軸に巻きついてしまい、解砕されなかった。
【０２２０】
−比較例７−
６５モル％の中和率を有するアクリル酸ナトリウムの水溶液５５００ｇ（単量体濃度３０重量％）に、ポリエチレングリコールジアクリレート（エチレンオキシドの数平均重合度＝８）９．２５ｇを溶解し反応液とした。次に、この反応液を窒素ガス雰囲気下で３０分間脱気した。次いで、シグマ型羽根を２本有する内容積１０Ｌのジャケット付ステンレス製双腕型ニーダーに蓋をつけて形成した反応器に、上記反応液を供給し、反応液を３０℃に保ちながら系を窒素ガス置換した。続いて、反応液を攪拌しながら、２、２’―アゾビス（２−アミジノプロパン）２塩酸塩１．９１ｇ、過硫酸ナトリウム０．９６ｇおよびＬ−アスコルビン酸０．１０ｇを添加したところ、およそ１分後に重合が開始した。そして３０℃から８０℃で重合を行い、重合を開始して６０分後に含水重合体を取り出した。得られた含水重合体は、その径が約５ｍｍに細分化されていた。この細分化された含水重合体を５０メッシュの金網の上に広げ、１５０℃で９０分間熱風乾燥した。ついで、乾燥物を振動ミルを用いて粉砕し、さらに２０メッシュの金網で分級することにより、重量平均粒径３００μｍの不定形破砕状の比較ベースポリマー（７）を得た。得られた比較ベースポリマー（７）１００部に、ジエチレントリアミンペンタ酢酸五ナトリウム０．００５部と、プロピレングリコール１部と、エチレングリコールジグリシジルエーテル０．０５部と、水３部と、イソプロピルアルコール１部とからなる表面表面架橋剤組成液を混合した。上記の混合物を２１０℃で４５分間加熱処理することにより、比較表面架橋吸水性樹脂（７）を得た。
【０２２１】
−比較例８−
３７重量％アクリル酸ナトリウム水溶液６７．０部、アクリル酸１０．２部、ポリエチリングリコールジアクリレート（エチレンオキシドの数平均重合度＝８）０．１５５部、および水２２．０部を混合し、単量体水溶液を調製した。バット中で前記水溶液に窒素を吹き込み、単量体水溶液中の溶存酸素を０．１ｐｐｍ以下にした。引き続き、窒素雰囲気下、前記水溶液の温度を１８℃に調整し、ついで５重量％過硫酸ナトリウム水溶液０．１６部、５重量％２、２’―アゾビス（２−アミジノプロパン）２塩酸塩水溶液０．１６部、０．５重量％Ｌ−アスコルビン酸水溶液０．１５部、および０．３５重量％過酸化水素水溶液０．１７部を順番に攪拌下、滴下した。過酸化水素滴下後、直ちに重合が開始し、１０分後に単量体水溶液の温度は８５℃のピーク温度に達した。引き続きバットを８０℃の湯浴に浸し、１５分間熟成した。得られた透明の含水重合体をミートチョッパーで砕き、この細分化された含水重合体を５０メッシュの金網の上に広げ、１６０℃で６５分間熱風乾燥した。ついで、乾燥物を粉砕機で粉砕し、さらに８５０μｍの篩を通過し１０６μｍの篩上に残るものに分級し、重量平均粒径３２０μｍの不定形破砕状の比較ベースポリマー（８）を得た。得られた比較ベースポリマー（８）１００部に、プロピレングリコール１部と、１，４−ブタンジオール０．５部と、水３部と、イソプロピルアルコール１部とからなる表面表面架橋剤組成液を混合した。上記の混合物を２１０℃で４０分間加熱処理することにより、比較表面架橋吸水性樹脂（８）を得た。
【０２２２】
また、実施例２、３、５、６の表面架橋吸水性樹脂（２）、（３）、（５）、（６）、比較例１、７、８の比較表面架橋吸水性樹脂（１）、（７）、（８）、比較例１、７、８の比較ベースポリマー（１）、（７）、（８）および、他社品の吸水性樹脂のＧＶ、ＡＡＰ、可溶化残存率、ＧＶ×可溶化残存率を比較した結果を表５に示す。
【０２２３】
【表５】

【０２２４】
【発明の効果】
合理的な工程で、無荷重下吸収倍率が高くて可溶分量の少ないベースポリマーおよび表面架橋を施した加圧下の吸収倍率の高い吸水性樹脂を提供することができる。
【０２２５】
上記効果を奏することから、本発明により得られた吸水性樹脂は、衛生用品（子供用および大人用おむつ、生理用ナプキン、成人用失禁製品など）などの人体に接する用途；植物や土壌の保水剤；電線あるいは光ケーブル用止水材；土木建築用止水材などに有用である。
【図面の簡単な説明】
【図１】実施例３および７〜１０における、重合反応温度と時間との関係を表したグラフ。時間ゼロは、光照射を開始した時である。
【図２】実施例１で得られた含水重合体の側面写真。
【図３】実施例３で得られた含水重合体の側面写真。
【図４】実施例３で得られた含水重合体の上面写真。
【図５】実施例３で得られた含水重合体の下面写真。
【図６】実施例５で得られた含水重合体の側面写真。
【図７】実施例７で得られた含水重合体の側面写真。
【図８】実施例７の含水重合体の一部を切り取り、水道水で膨潤させたゲルの写真。[0001]
BACKGROUND OF THE INVENTION
  The present invention polymerizes a monomer component that becomes a water-absorbing resin by polymerizing with an aqueous solution, and is suitable for use in various applications such as sanitary goods such as disposable diapers and sanitary napkins, and a water retention agent for soil. Those who manufacture resinTo the lawIt is related.
[0002]
[Prior art]
In recent years, water-absorbent resins have been widely used and produced and consumed in large quantities for various uses such as paper diapers, sanitary napkins, sanitary products such as adult incontinence products, and water retention agents for soil.
[0003]
Especially in sanitary products such as paper diapers, sanitary napkins and incontinence products for adults, there is a tendency to increase the amount of water-absorbent resin and reduce the amount of pulp fiber used to make the product thinner. For example, a large absorption capacity under pressure is desired. On the other hand, since a large amount of use per sanitary product is required, a low-cost water-absorbing resin is desired. Therefore, it is desired to reduce the energy consumption in the production line of the water-absorbent resin, reduce the emissions, and establish a rational production method using them.
[0004]
Polymerization at a high monomer concentration or high temperature to reduce the cost to improve the performance / cost ratio of the water absorbent resin when polymerizing the monomer component that becomes a water absorbent resin by polymerization. Various polymerization methods have been tried in the past to obtain a water-absorbent resin which is dried at once by starting polymerization and evaporating water by polymerization heat or heating.
[0005]
JP-A-58-71907 (Arakawa Chemical) and JP-A-59-18712 (Arakawa Chemical) describe a method of polymerizing an aqueous acrylate solution having a concentration higher than 55% by weight to obtain a water-absorbent resin dry solid all at once. In US Pat. No. 4,985,518 (American colloid), a water-absorbent resin dry solid is obtained at once by polymerizing an aqueous acrylate solution having a concentration higher than 30% by weight. In JP-A-55-58208 (Kitani), polymerization is carried out at a polymerization temperature of 106 to 160 ° C. without using a cross-linking agent, and according to the examples, a dry solid with little moisture at the end of the polymerization. Japanese Patent Application Laid-Open No. 1-318022 (Mitsubishi Yuka) discloses a method of polymerizing an aqueous solution containing 45 to 80% by weight of a monomer having a neutralization rate of 20 to 50 mol% to obtain a substantially dry polymer. Yes. However, these methods have a drawback that the amount of soluble component is large relative to the absorption capacity of the produced water-absorbent resin.
[0006]
In JP-A-55-147512 (Sumitomo Chemical), JP-A-56-147809 (Sumitomo Chemical), JP-A-63-275607 (Sanyo Chemical), and JP-A-63-275608 (Sanyo Chemical), An aqueous solution is supplied onto a heated rotating drum and scraped to obtain a dried product of the water absorbent resin all at once. Similar to JP-A-1-165610 (Rohm and Haas), an aqueous monomer solution is supplied onto the heated surface to obtain a substantially dry water-absorbing resin solid. However, these methods also have the disadvantage that the amount of soluble component is large for the absorption capacity of the water absorbent resin to be produced.
[0007]
In JP-A-2-215801 (Mitsubishi Yuka), polymerization is performed by spraying a monomer aqueous solution heated using the heat of neutralization of the monomer into the gas phase, but the polymerization is completed in about 3 seconds. Therefore, it is considered difficult to control the polymerization.
[0008]
Although the above prior art is a technique published before 1990, it seems that it has not been implemented in practice because it has its respective drawbacks.
[0009]
Thereafter, in order to improve the performance / cost ratio of the water-absorbent resin, techniques for improving the performance have been disclosed. In JP-A-4-175319 (Sanyo Kasei) and JP-A-11-181005 (Nippon Catalysts), polymerization is started at a low temperature, polymerized gently while removing heat, and the peak temperature is suppressed to about 90 ° C. or less to achieve high performance. Attempts have been made to obtain water absorbent resins. In JP-A-11-228604 (Nippon Catalyst), the polymerization is also started at a low temperature, the polymerization is gently performed while removing heat, and the peak temperature is suppressed to about 95 ° C. or lower, or the solid content concentration increase is 0.2 to Attempts have been made to obtain a high-performance water-absorbing resin by controlling the content within the range of 10% by weight. Japanese Patent Application Laid-Open No. 9-67404 (BASF) and US Pat. No. 6,187,828 (BASF) disclose a method of initiating polymerization at a low temperature in a tube-type cylindrical polymerization reactor and performing adiabatic polymerization. In other words, the concentration of the aqueous monomer solution cannot be increased, and the residence time is increased (several hours). Since these are all at the expense of productivity, an increase in cost is inevitable.
[0010]
Recently, Journal of Applied Polymer Science, Vol. 74, 119-124 (1999) reported “An Effective Preparation Method for Superabsorbent Polymers” (Chen, Zhao). For this purpose, a low-cost polymerization method has been proposed in which an aqueous solution having a monomer concentration of 43.6% and an initiator are placed in a stainless steel petri dish and immersed in a 70 ° C. or 80 ° C. water bath for polymerization. However, it has not reached an industrially useful level.
[0011]
Japanese Patent Laid-Open No. 10-45812 (Sekisui Plastics) attempts to suppress bumping by adding short fibers to the monomer aqueous solution, promote radiation of water vapor, and lower the moisture value of the generated gel. The disadvantage is that expensive short fibers that do not contribute to water absorption are used.
[0012]
[Problems to be solved by the invention]
  The object of the present invention is to produce a water-absorbing resin with excellent performance at low cost.The lawIt is to provide. Specifically, in a reasonable process, a base polymer with a high absorption capacity under no load and a low soluble content and a water absorbent resin with a high absorption capacity under pressure that has undergone surface crosslinkingThe lawIt is to provide.
[0013]
[Means for Solving the Problems]
As a result of diligent investigations to achieve the above object, the present inventor has found that the conventional theory (the above-mentioned JP-A-4-175319 (Sanyo Kasei), JP-A-11-181005 (Nippon Catalyst), JP-A-11-228604 (Nippon Catalyst) In contrast to the theory that high-performance water-absorbent resin can be obtained by starting polymerization at a low temperature and reducing the peak temperature as much as possible by removing heat, as in ()). Higher water-absorbing resin can be obtained with high productivity in a rough manner from the conventional idea of increasing the water content at the boiling temperature of the gel to obtain a high solid content water-containing polymer in a short time. As a result, the present invention has been completed. Here, the “hydrated polymer” refers to a water-containing water-absorbent resin having a solid content concentration of 82% by weight or less.
[0014]
In addition, in the production method of the present invention, it is important how a water-containing polymer having a high solid content concentration of 55 to 82% by weight that can be produced by polymerization can be crushed. The water-containing polymer produced by polymerizing a monomer component that becomes a water-absorbing resin by aqueous polymerization is usually crushed when it is difficult to dry as it is, such as thick plate, block, or sheet It becomes a water-absorbent resin product through each process such as drying, pulverization, classification, and surface treatment. In the case of an acrylic acid (salt) water-absorbing resin, when the solid content concentration of the hydrous polymer is less than 55% by weight, it can be easily crushed by a meat grinder (meat chopper) type pulverizer or the like. Further, when the solid content concentration exceeds 82% by weight, it can be easily pulverized by a normal impact type pulverizer or the like in the same manner as the dried polymer. However, a water-containing polymer having a solid content concentration of 55% by weight or more and 82% by weight or less is difficult to handle due to its properties, and so far, attempts to disintegrate industrially have not been successful.
[0015]
For example, in Comparative Examples 1 and 2 of US Pat. No. 4,703,067 (American colloid), water-containing polymers having solids concentrations of 58% and 67% were obtained, respectively. ”And avoids crushing in the above solid content concentration region.
[0016]
JP-A-4-175319 (Sanyo Kasei) exemplifies a gel crusher, but it is polymerized at a maximum monomer concentration of 50% by weight, and a hydropolymer having a solid content concentration of 55% by weight or more is disclosed. No examples are shown.
[0017]
In JP-A-10-119042 (Nippon Catalysts), JP-A-11-188725 (Nippon Catalysts), and JP-A-11-188726 (Nippon Catalysts), the gel is crushed by shearing with a fixed blade and a rotary blade. An example of crushing a water-containing polymer having a solid content concentration of not less than wt% is not shown.
[0018]
In JP-A-11-188727 (Nippon Shokubai, Hatsuda, Miyake, Yano), a water-containing polymer is crushed by being sandwiched and sheared by a pair of spiral rotating blades that are provided opposite to each other and have different feed rates. Is disclosed. In Example 1, the water-containing polymer having a water content of 39% by weight is crushed, but it is not illustrated that the water-containing polymer having a weight average particle size of 100 mm or less is crushed. Actually, the weight average particle diameter of the crushed water-containing polymer exceeded 100 mm.
[0019]
Therefore, as a result of earnestly examining how the water-containing polymer having a high solid content concentration of 55 to 82% by weight that can be generated by polymerization can be crushed, the present inventor uses a specific pulverizer. It was also found that it can be subdivided more easily.
[0020]
  That is, the method for producing a water-absorbent resin according to the present invention is a method for producing a water-absorbent resin by polymerizing a monomer component mainly composed of acrylic acid and / or a sodium salt thereof in an aqueous solution.
  (1) The concentration of the monomer component in the aqueous solution is 45% by weight or more,
  (2) polymerizing while evaporating moisture so that the ratio (concentration ratio) of the solid content concentration of the hydrous polymer produced by polymerization and the solid content concentration in the monomer aqueous solution is 1.10 or more;
  (3) The solid content concentration of the hydropolymer produced by polymerization is 80% by weight or less,
  (4) Subdividing the hydrous polymer produced by polymerization, followed by drying and grinding,
It is characterized by.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0040]
Examples of the monomer component to be polymerized to be a water-absorbent resin used in the present invention include (meth) acrylic acid, (anhydrous) maleic acid, itaconic acid, cinnamic acid, vinyl sulfonic acid, allyl toluene sulfonic acid, Vinyltoluenesulfonic acid, styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2-hydroxyethyl (meth) Anionic unsaturated monomers such as acryloyl phosphate and salts thereof; mercaptan group-containing unsaturated monomers; phenolic hydroxyl group-containing unsaturated monomers; (meth) acrylamide, N-ethyl (meth) acrylamide, N Amide group-containing unsaturated monomers such as N, N-dimethyl (meth) acrylamide; N, N-dimethyl Aminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) amino group-containing unsaturated monomer acrylamide. These monomers may be used singly or may be used in combination of two or more, but acrylic acid and / or a salt thereof (for example, sodium) from the viewpoint of performance and cost of the resulting water-absorbent resin It is necessary to use a salt of lithium, potassium, ammonium, amines, etc., among which a sodium salt is preferable from the viewpoint of cost) as a main component. Preferably, acrylic acid and / or a salt thereof is 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, based on all monomer components.
[0041]
In addition to unsaturated monomer components such as acrylic acid and / or a salt thereof and an internal cross-linking agent, the solid content in the monomer aqueous solution herein includes other additives such as a polymerization initiator described later. .
[0042]
A conventionally known internal cross-linking agent can be used as the internal cross-linking agent. Specifically, the method described in JP-A-10-182750, p. 4 is an internal cross-linking agent. Among these, one or more kinds can be used in consideration of reactivity. Especially, it is preferable to use the compound which has a 2 or more polymerizable unsaturated group essential. The amount of these used can be appropriately determined depending on the properties of the water-absorbing resin to be obtained.
[0043]
The concentration of the monomer component to be polymerized to become a water absorbent resin is not particularly limited, but is preferably 30% by weight or more, more preferably 35% by weight or more, still more preferably 40% by weight or more, and further preferably 45% by weight. % Or more, more preferably 50% by weight or more, more preferably 55% by weight or more, further preferably 30 to 70% by weight, further preferably 35 to 60% by weight, and further preferably 40 to 60% by weight. If it is less than 30% by weight, the productivity is low, and if it exceeds 70% by weight, the absorption capacity is low.
[0044]
The neutralization rate of the acid group-containing monomer is not particularly limited, but for applications that may come into contact with the human body, such as sanitary goods, 50 mol% or more is necessary, including the fact that neutralization after polymerization is not required. Is preferred. More preferably, they are 50 mol% or more and less than 80 mol%, More preferably, they are 55 mol% or more and 78 mol% or less, Most preferably, they are 60 mol% or more and 75 mol% or less.
[0045]
When acrylic acid is used after being neutralized with an alkali, it is preferable to effectively use the heat of neutralization and / or the heat of dissolution (of acrylic acid and alkali) to raise the temperature of the monomer aqueous solution. In a preferred embodiment, polymerization is initiated by adding a crosslinking agent and an initiator to the aqueous monomer solution heated by neutralization in an adiabatic state. Alternatively, as will be described later, heat of neutralization and / or heat of dissolution (of acrylic acid and alkali) is utilized to remove dissolved oxygen.
[0046]
Upon polymerization, the reaction system includes starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), polyacrylic acid (salt) cross-linked hydrophilic polymers, and hypophosphorous acid (salt). A chain transfer agent such as a chelating agent may be added.
[0047]
The polymerization method of the monomer component is not particularly limited as long as it is aqueous solution polymerization, and is a static polymerization method in which a monomer aqueous solution is polymerized in a stationary state, and a stirring polymerization method in which polymerization is performed in a stirring device. The present invention can be implemented by, for example.
[0048]
In the static polymerization method, it is preferable to use an endless belt. The belt is preferably a resin or rubber belt that does not allow the heat of polymerization to escape from the contact surface.
[0049]
In the stirring polymerization method, a uniaxial stirrer is possible, but a stirrer having a plurality of stirring shafts is preferably used.
[0050]
Generally, in radical aqueous solution polymerization, before introducing a polymerization initiator, an inert gas is blown or degassed under reduced pressure to remove dissolved oxygen that hinders polymerization, but this requires equipment and operating costs. It is the actual situation. In a preferred embodiment of the present invention, the operation of removing dissolved oxygen is performed by using the heat of neutralization and / or the heat of dissolution (of acrylic acid and alkali) described above to raise the temperature of the monomer aqueous solution and volatilize the dissolved oxygen. To do.
[0051]
In a more preferred embodiment, acrylic acid, an alkaline aqueous solution, water, etc., which are raw materials for the monomer aqueous solution, are heated by neutralization without deoxygenation in advance, and the dissolved oxygen amount is set to the monomer aqueous solution, It is preferably 4 ppm or less, more preferably 2 ppm or less, and most preferably 1 ppm or less, and can be used for polymerization without deoxidation as it is.
[0052]
It is also preferable to partially deoxygenate a part or all of acrylic acid, an alkaline aqueous solution, water, etc., which are raw materials for the monomer aqueous solution, and further deoxygenate by raising the temperature by neutralization. In addition, when the acrylic acid and alkali are neutralized by line mixing and the polymerization initiator is further line mixed to start polymerization at a high temperature of 80 ° C. or higher, the raw material acrylic acid is used to prevent the polymerization from starting in the line. It is preferable that an alkaline aqueous solution, water and the like are not deoxygenated in advance.
[0053]
The polymerization is usually carried out under normal pressure, but it is also a preferred embodiment that water is distilled off under reduced pressure in order to lower the boiling temperature of the polymerization system. For ease of operation, etc., it is more preferably carried out under normal pressure.
[0054]
The increase in the neutralization rate during the polymerization is not particularly limited, but is preferably 2 points or more, more preferably 3 points or more, more preferably 4 points or more. Even if the neutralization rate increase is 0, there is no particular problem, but if it is 2 points or more, it is preferable in view of improving the physical properties of the obtained polymer (water-containing polymer, base polymer, water-absorbing resin).
[0055]
The polymerization initiator used in the present invention is not particularly limited, and is a thermal decomposition type initiator (for example, persulfate: sodium persulfate, potassium persulfate, ammonium persulfate; peroxide: hydrogen peroxide, t- Butyl peroxide, methyl ethyl ketone peroxide); azo compound: azonitrile compound, azoamidine compound, cyclic azoamidine compound, azoamide compound, alkylazo compound, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [ 2- (2-imidazolin-2-yl) propane] dihydrochloride), photodegradable initiators (for example, benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, azo compounds) and the like can be used. Persulfate is preferred because of its cost and ability to reduce residual monomer. It is also a preferable method to use a photolytic initiator and ultraviolet rays. More preferably, a photodegradable initiator and a thermal decomposable initiator are used in combination.
[0056]
The monomer temperature is preferably increased in advance. The reason for this is that the above-described removal of dissolved oxygen is facilitated, and the preferable polymerization start temperature described below can be immediately realized. The monomer temperature is not particularly limited, but is usually 50 ° C. or higher, preferably 60 ° C. or higher, more preferably 70 ° C. or higher, more preferably 80 ° C. or higher, more preferably 90 ° C. or higher, more preferably 80 to 105 ° C, most preferably 90 to 100 ° C. If it is less than 50 ° C., not only the productivity is lowered due to the prolonged induction period and polymerization time, but also the physical properties of the water-absorbent resin are lowered. The polymerization time refers to the time from when the monomer aqueous solution is placed in the polymerization vessel and the polymerization start conditions are satisfied to the peak temperature.
[0057]
The polymerization initiation temperature is usually 50 ° C. or higher, preferably 60 ° C. or higher, more preferably 70 ° C. or higher, more preferably 80 ° C. or higher, more preferably 90 ° C. or higher, more preferably 80 ° C. to 105 ° C., and most preferably 90 ° C. ~ 100 ° C. When the polymerization initiation temperature is less than 50 ° C., not only the productivity is lowered due to the extension of the induction period and the polymerization time, but the physical properties of the water absorbent resin are also lowered. When the polymerization start temperature exceeds 105 ° C., foaming and stretching may not be sufficiently performed. The polymerization initiation temperature can be observed by the cloudiness of the aqueous monomer solution, the increase in viscosity, the increase in temperature, and the like.
[0058]
In order to ensure the temperature of the aqueous monomer solution and initiate polymerization, as described above, the heat of neutralization of the aqueous monomer solution and / or the heat of dissolution (of acrylic acid and alkali) should be used. Is preferred.
[0059]
The maximum temperature reached during the polymerization is not particularly limited, but is preferably 150 ° C. or lower, more preferably 140 ° C. or lower, more preferably 130 ° C. or lower, more preferably 120 ° C. or lower, more preferably 115 ° C. or lower. If it exceeds 150 ° C., it is not preferable in that the physical properties of the obtained polymer (water-containing polymer, base polymer, water-absorbing resin) are significantly lowered.
[0060]
In the present invention, the difference ΔT between the polymerization initiation temperature and the highest temperature reached during the polymerization is preferably 70 ° C. or less, more preferably 60 ° C. or less, further preferably 50 ° C. or less, more preferably 40 ° C. or less, More preferably, it is 30 degrees C or less, Most preferably, it is 25 degrees C or less. When ΔT is higher than 70 ° C., it is not preferable in that the physical properties of the resulting polymer (hydropolymer, base polymer, and water-absorbing resin) are lowered.
[0061]
The polymerization time is not particularly limited, but is preferably 5 minutes or less, more preferably 3 minutes or less, more preferably less than 3 minutes, more preferably 2 minutes or less, more preferably 1 minute or less. If it exceeds 5 minutes, it is not preferable in that the productivity of the resulting polymer (water-containing polymer, base polymer, and water-absorbing resin) decreases.
[0062]
According to a preferred example of the polymerization method of the present invention, after the polymerization is started, the temperature of the system rapidly increases to reach the boiling point at a low polymerization rate, for example, 10 to 20 mol%, emits water vapor, and increases the solid content concentration. However, polymerization proceeds. The polymerization heat is effectively used to increase the solid content concentration. Therefore, it is desirable to suppress the heat radiation from the contact portion of the polymerization vessel as much as possible, and the material is preferably a resin, rubber, stainless steel non-contact portion covered with a heat insulating material, or heated by a jacket. Used. Since the water vapor generated from the system may contain a monomer, it is desirable to recover and use it in that case. In particular, it is preferable to collect and recycle acrylic acid and / or water that evaporates during the polymerization. The recovery rate of acrylic acid is preferably 1% or more, more preferably 2% or more, and still more preferably 3% or more with respect to the total weight of acrylic acid used (before neutralization).
[0063]
In addition, the method of the present invention is characterized by polymerization at a high temperature from the start of polymerization, and is presumed to be a cause of high performance. In the polymerization under normal pressure, the polymerization is such that the temperature is already 100 ° C. or higher when the polymerization rate is 40 mol%, and the temperature is still 100 ° C. or higher even when the polymerization rate is 50 mol%. Polymerization in which the temperature is already 100 ° C. or higher when the polymerization rate is 30 mol% and the temperature is still 100 ° C. or higher even when the polymerization rate is 50 mol% is a more preferable embodiment. The most preferable embodiment is such that the temperature is already 100 ° C. or higher when the polymerization rate is 20 mol%, and the temperature is still 100 ° C. or higher even when the polymerization rate is 50 mol%. In the case of low pressure polymerization, the boiling temperature is already reached when the polymerization rate is 40 mol%, and the boiling temperature is still preferable even when the polymerization rate is 50 mol%. The polymerization is such that the boiling point is already at the boiling point when the polymerization rate is 30 mol%, and the boiling point is still at the boiling point even when the polymerization rate is 50 mol%, and the boiling temperature is already reached when the polymerization rate is 20 mol%. Polymerization that is still at the boiling temperature even at a rate of 50 mol% is the most preferred embodiment.
[0064]
As described above, since the temperature becomes high at a low polymerization rate, the polymerization time is also short, and it usually ends in 10 minutes or less, preferably 5 minutes or less. The polymerization time here refers to the time from when the monomer aqueous solution to which the polymerization initiator is added to the polymerization vessel to when the water-containing polymer is taken out from the polymerization vessel.
[0065]
In the present invention, the ratio (concentration ratio) between the solid content concentration of the water-containing polymer produced by polymerization and the solid content concentration of the monomer aqueous solution is preferably 1.10 or more, more preferably 1.15 or more, still more preferably It is desirable to polymerize while evaporating water so that is not less than 1.20, more preferably not less than 1.25. When the concentration ratio is less than 1.10, it cannot be said that the heat of polymerization is sufficient. Here, the solid content of the monomer aqueous solution is a monomer and other additives, and does not include water or a solvent.
[0066]
In the present invention, the polymerization temperature rise ratio, that is, the ratio of ΔT (difference between the highest temperature reached during polymerization and the polymerization initiation temperature, ° C.) observed in the polymerization system and the theoretical ΔT (° C.) (Shown in the examples) is preferably 0.30 or less. More preferably, it is 0.25 or less, More preferably, it is 0.20 or less. A polymerization temperature rise ratio of greater than 0.30 is preferred in that the heat of polymerization heat is insufficiently used for water evaporation, and the physical properties of the resulting polymer (water-containing polymer, base polymer, and water-absorbing resin) are reduced. Absent.
[0067]
The water-containing polymer obtained by the above polymerization preferably has a solid content concentration of 82% by weight or less, more preferably 80% by weight or less, more preferably 75% by weight or less. Also, preferably 50% to 82% by weight, more preferably 55% to 82% by weight, more preferably 60% to 78% by weight, more preferably 60% to 75% by weight, more preferably 60% by weight. % To 73% by weight, more preferably 66% to 73% by weight. When this solid content concentration exceeds 82% by weight, the performance is decreased, that is, the absorption capacity is decreased and the soluble content is increased. Moreover, when this solid content concentration is less than 50 weight%, it is not preferable at the point which the burden of drying of a post process is large.
[0068]
The water-containing polymer preferably has a form formed by foaming expansion and contraction during polymerization. This is a form in which the polymerization system is foamed with a diameter of cm to mm by boiling water pressure due to boiling at the time of polymerization, the surface area is increased, vaporization of water vapor is thereby caused, and then shrinkage occurs. (Shown in the photos of FIGS. 3-7). In addition, this form has an unexpected feature that the releasability from the polymerization vessel is improved or the hydrated polymer is easily crushed.
[0069]
The method for measuring the expansion ratio during polymerization was described in the examples. The expansion ratio during the polymerization is preferably 2 times or more, more preferably 3 times or more, more preferably 5 times or more, more preferably 10 times or more, more preferably 20 times or more. At the time of expansion, since the polymerization system is stretched, the polymerization proceeds while being stretched.
[0070]
The water-containing polymer can be dried and pulverized after being subdivided to obtain a base polymer (water-absorbing resin before surface treatment).
[0071]
When the obtained base polymer was observed with a microscope, even when the polymerization was accompanied by foaming, most of the particles were in an amorphous state containing no bubbles, probably because the bubble size was relatively large.
[0072]
In the production method of the present invention, the base polymer may be subjected to surface cross-linking treatment, whereby a water-absorbing resin having a large absorption capacity under pressure can be obtained. For the surface cross-linking treatment, a known surface cross-linking agent and a known surface cross-linking method which are usually used for the application can be used.
[0073]
In this specification, the terms water-containing polymer, base polymer, and surface-crosslinked water-absorbing resin are used, and all are terms representing one form of the water-absorbing resin.
[0074]
In the production method of the present invention, it is important how the water-containing polymer having a high solid content of 55 to 82% by weight that can be produced by polymerization can be crushed. The water-containing polymer produced by polymerizing a monomer component that becomes a water-absorbing resin by aqueous polymerization is usually crushed when it is difficult to dry as it is, such as thick plate, block, or sheet It becomes a water-absorbent resin product through each process such as drying, pulverization, classification, and surface treatment. In the case of an acrylic acid (salt) water-absorbing resin, when the solid content concentration of the hydrous polymer is less than 55% by weight, it can be easily crushed by a meat grinder (meat chopper) type pulverizer or the like. Further, when the solid content concentration exceeds 82% by weight, it can be easily pulverized by a normal impact type pulverizer or the like in the same manner as the dried hydropolymer. However, a water-containing polymer having a solid content concentration of 55% by weight or more and 82% by weight or less is difficult to handle due to its properties, and so far, attempts to disintegrate industrially have not been successful.
[0075]
Therefore, the present inventor has intensively studied how to hydrolyze a water-containing polymer having a high solid content concentration of 55 to 82% by weight that can be produced by polymerization. It has been found that it can be easily subdivided by using (in the present patent application, these are represented by the word “cracker”).
[0076]
There is no particular limitation on the shape of the hydropolymer having a solid content concentration of 55 to 82% by weight to be crushed, but it is preferably a plate or sheet having a thickness of 3 cm or less, more preferably a thickness. Plate or sheet of 2 cm or less, more preferably plate or sheet of 1 cm or less, more preferably plate or sheet of 5 cm or less in the form of a lot of wrinkles formed by foaming expansion and contraction during polymerization It is in the form of a sheet.
[0077]
As a device for crushing a water-containing polymer having a solid content concentration of 55 to 82% by weight in the present invention, a crusher having a screen is preferable. Furthermore, as the pulverizer, a shearing type pulverizer or cutting / shearing mill classified in Table 16.4 of Table 16.4 of Chemical Engineering Handbook (6th revised edition, edited by Chemical Engineering Society, Maruzen Co., Ltd., 1999) is used. A corresponding device is preferred. Furthermore, it is preferable that the apparatus be crushed by shearing between the fixed blade and the rotary blade. By crushing with these apparatuses, it is possible to easily crush a hydrous polymer having a high solid content concentration of 55 to 82% by weight, which has been difficult in the past.
[0078]
Specific examples of the shearing type crusher or cutting / shearing mill are given below.
Saw, circular saw, band saw (BAND SAW)
Vertical crusher (VERTICAL CUTING MILL Co., Ltd. Orient)
Rotoplex (ROTOPLEX, Hosokawa Micron Corporation)
Turbo cutter (TURBO CUTTER, Turbo Industry Co., Ltd.)
Turbo grinder (TURBO GRINDER, Turbo Industry Co., Ltd.)
Tire shredder (TYRE SHREDDER, Masuno Seisakusho Co., Ltd.)
Rotary cutter mill (ROTARY CUTTER MILL, Yoshida Manufacturing Co., Ltd.)
Cutter mill (CUTTER MILL, Tokyo Atomizer Manufacturing Co., Ltd.)
Shred crusher (SHRED CRUSHER, Tokyo Atomizer Manufacturing Co., Ltd.)
Cutter mill (CUTTER MILL, Masuko Sangyo Co., Ltd.)
Crusher (CRUSHER, Masuko Sangyo Co., Ltd.)
Rotary cutter mill (ROTARY CUTTER MILL, Nara Machinery Co., Ltd.)
GAINAX CRUSHER (Horai Co., Ltd.)
Yucom (U-COM, Horai Co., Ltd.)
Mesh mill (MESHMILL, Horai Co., Ltd.)
In the present invention, when a water-containing polymer having a solid content concentration of 55 to 82% by weight is crushed using a crusher, the solid content concentration is increased by 2 points or more (for example, a water content weight of 70% by weight of solid content concentration). By crushing the coalesced to a solid content concentration of 72% by weight, it will increase by 2 points), or by aeration of gas, preferably dry air in the crusher, or both. It has been found that even a crusher can crush such a water-containing polymer that is difficult to crush.
[0079]
The solid content increase is more likely to be crushed as the increase rate increases from 2 points to 3 points and 4 points, and as the ventilation rate increases, but it should be selected in view of economic efficiency. At the time of pulverization, water vapor generated from the water-containing polymer is condensed in the apparatus, and the water-containing polymer is easily attached and blocked in the apparatus, but it is considered that such a phenomenon is less likely to occur due to ventilation.
[0080]
In the crushing, a surfactant described in JP-A-11-188726 (Nippon Catalysts) may be added. However, the higher the solid content concentration of the water-containing polymer, the less the necessity.
[0081]
The weight average particle size of the water-containing polymer crushed by the crushing means of the present invention is preferably 100 mm or less, more preferably 10 mm or less, further preferably 3 mm or less, and most preferably 1 mm or less. Ideally, it can be crushed to the final product particle size in the state of a hydrous polymer.
[0082]
The amount of residual monomer in the particulate hydropolymer crushed by the crushing means of the present invention is not particularly limited, but is preferably 3000 ppm or less in order to prevent the residual monomer from being scattered during drying or the like in the subsequent step. Depending on the application, it is preferably 1000 ppm or less, more preferably 500 ppm or less, and most preferably 300 ppm or less. In particular, when it is used as a particulate hydrous polymer for sanitary goods such as paper diapers, it is preferably 1000 ppm or less, and more preferably 500 ppm or less.
[0083]
The water-containing polymer (particulate water-containing polymer) crushed by the crushing means of the present invention preferably has a solid content concentration of 55 to 82% by weight, a residual monomer amount of 1000 ppm or less, and a weight average particle size of 3 mm or less. It is.
[0084]
The crushed water-containing polymer (particulate water-containing polymer) having a solid content concentration of 55 to 82% by weight, residual monomer of 1000 ppm or less and a weight average particle size of 3 mm or less of the present invention is once dried (solid What is made by adding water to those having a partial concentration of 83% by weight or more is not included.
[0085]
In the production method of the present invention, the hydropolymer after crushing may be dried. Although there is no restriction | limiting in particular in a drying method, The drying method which contacts a hot air and a heat-transfer surface well like moving a material like a stirring drying method, a fluidized-bed drying method, an airflow drying method, etc. is used preferably.
[0086]
In the production method of the present invention, the subsequent handling of the crushed water-containing polymer (particulate water-containing polymer) can be selected from the following methods.
[0087]
(1) Commercialization of the particulate hydrous polymer as it is; use as it is for sanitary goods, agriculture and horticulture. For the fluidity of the particles, a particulate inorganic substance (bentonite, zeolite, silicon oxide, etc.) may be mixed.
[0088]
(2) Mixing and reacting a particulate water-containing polymer with a surface cross-linking agent to produce a product in a water-containing state; no energy is required to evaporate water. For the fluidity of the particles, a particulate inorganic substance (bentonite, zeolite, silicon oxide, etc.) may be mixed.
[0089]
(3) Mixing and reacting a particulate water-containing polymer with a surface crosslinking agent and drying to produce a product; the heating energy for drying can also be used as the energy for the surface crosslinking reaction.
[0090]
(4) Dry the particulate water-containing polymer and commercialize it as it is
(5) Dry the particulate water-containing polymer, grind and classify it, and commercialize it
(6) Dry particulate water-containing polymer, pulverize, classify and surface cross-link to produce product
Conventionally, the following can be newly achieved by pulverizing a hydrous polymer having a solid content concentration of 55 to 82% by weight, which has been difficult to pulverize, and obtaining a particulate hydrous polymer.
[0091]
1) The above methods (1), (2) and (3) are possible.
[0092]
2) The drying of a hydropolymer having a solid content concentration of less than 55% by weight was difficult to use as a drying method unless a compound having a releasing action such as a surfactant was added; A drying method such as a fluidized bed drying method or an airflow drying method that makes good contact with hot air or a heat transfer surface while moving the material can be employed.
[0093]
3) Since the polymer can be crushed in a water-containing state, a particulate water-containing polymer with little fine powder hardly generated is obtained.
[0094]
Another preferred production method according to the present invention is a method for producing a water-absorbent resin by polymerizing a monomer component mainly composed of acrylic acid and / or a salt thereof in an aqueous solution.
(1) a polymerization step for producing a hydropolymer having a solid content concentration of 55 to 82% by weight;
(2) a crushing step of crushing a water-containing polymer having a solid content concentration of 55 to 82% by weight to a weight average particle size of 10 mm or less;
(3) A drying step for increasing the solid content concentration of the crushed water-containing polymer by 3% or more,
And a method for producing a water-absorbent resin, characterized in that By providing these three steps, it is possible to provide a method for producing a water-absorbing resin with excellent performance at low cost, and in a rational step, a base polymer having a high absorption capacity under no load and a low soluble content. In addition, it is possible to provide a water-absorbent resin having a high absorption capacity under pressure and subjected to surface crosslinking.
[0095]
The present invention also provides a novel water-absorbing resin that works well in applications such as sanitary goods, is not bulky when discarded after use, and is easily decomposed into a linear polymer. Conventionally, disposal methods after sanitary goods such as disposable diapers and sanitary napkins containing water-absorbing resins have been used by consumers include (1) combustion (2) landfill (3) combustion after volume reduction treatment (4 ) Toilet flushing (5) Composting (6) Others. Many studies and surveys have been conducted on the impact of discarded water-absorbing resins on the environment, and it has been reported that there is no problem. However, when sanitary goods after use are buried in the soil, the water-absorbent resin absorbs the soil water and swells greatly, so it is considered to occupy a disposal place and space, and has been a problem until now. In the future, it is desirable to take this into consideration, and for that purpose, it is desirable to solubilize or decompose in the environment.
[0096]
Therefore, many studies on biodegradable water-absorbing resins have been conducted.
[0097]
For example, JP-A-11-255896 (Mitsui Chemicals), JP-A-2001-114803 (Unitika), JP-A-8-59820, JP-A-8-196901, JP-A-8-89974, JP-A-9-124754, JP-A-9-216914. (Nippon Catalyst) However, these materials are not yet put into practical use because of the high raw materials and complicated processes or because they are expensive products, and the performance is not as good as that of acrylic water-absorbing resins. Currently.
[0098]
JP 2001-104929 (Nippon Asahi Kiko Co., Ltd.) proposes a volume reduction treatment method for used paper diapers, and the water-absorbent resin after use is desired to have a small volume.
[0099]
A sanitary article containing a water-absorbing resin and flowing into a flush toilet has also been devised (Japanese Patent Laid-open No. Hei 6-210166, US Pat. No. 5,415,643, Kimberly Clark). Since the water-absorbent resin swells in the drain pipe, the possibility of filling the pipe increases. Therefore, it is desirable that the water-absorbent resin is solubilized or decomposed when it is poured into a flush toilet.
[0100]
Moreover, although it is thought that the waste water-absorbing resin produced in the manufacturing process of the water-absorbing resin is burnt, there is an attempt to make effective use of this. For example, in US Pat. No. 6,143,820 (Dow), an acrylic acid water-absorbing resin is decomposed and used as a linear polymer as a dispersant, a scale inhibitor, and a detergent additive.
[0101]
The present invention provides a novel water absorbent resin that solves these problems.
[0102]
That is, the water-absorbent resin according to the present invention is a water-absorbent resin obtained by polymerizing a monomer component mainly composed of acrylic acid and / or a salt thereof in an aqueous solution,
(1) 20 (g / g) ≦ absorption capacity under no load (GV) ≦ 60 (g / g),
(2) Absorption capacity under pressure (AAP) ≧ 20 (g / g),
(3) Absorption capacity under no load (GV) × Solubilization residual ratio (%) ≦ 1200 ((g / g)%),
It has the physical property which becomes.
[0103]
The unloaded absorption capacity (GV) is preferably 25 to 55 (g / g), more preferably 25 to 50 (g / g). If it is less than 20 (g / g), it is not economical, and if it is more than 60 (g / g), it is not preferable in that a practical gel strength cannot be obtained.
[0104]
The absorption capacity under pressure (AAP) is preferably 25 (g / g) or more, more preferably 30 (g / g) or more, and more preferably 35 (g / g) or more. If it is less than 20 (g / g), the resulting water-absorbent resin is not preferred because it does not exhibit desirable performance when used in sanitary goods at a high concentration.
[0105]
The value of absorption capacity under no load (GV) × solubilization residual rate (%) is preferably 1000 ((g / g)%) or less, more preferably 800 ((g / g)%) or less, and more. Preferably, it is 600 ((g / g)%) or less. When it is larger than 1200 ((g / g)%), the resulting water-absorbent resin is not preferable in that it is difficult to be decomposed and solubilized.
[0106]
The water absorbent resin is a water absorbent resin obtained by polymerizing a monomer component mainly composed of acrylic acid and / or a salt thereof in an aqueous solution,
1) The concentration of the monomer component in the aqueous solution is 50% by weight or more,
2) The amount of the internal crosslinking agent is 0.02 mol% or less of the whole monomer component,
3) Surface crosslinking treatment is applied
4) 10 ppm or more of chelating agent is added,
It is characterized by.
[0107]
That is, the concentration of the monomer aqueous solution needs to be 50% by weight or more, preferably 53 to 70% by weight. The amount of the internal crosslinking agent needs to be 0.02 mol% or less of the whole monomer component, preferably 0.01 mol% or less, more preferably 0.005 mol% or less. Furthermore, it is necessary that a surface cross-linking treatment is performed, and the GV of the surface cross-linked product is preferably 80% or less of the GV of the base polymer, more preferably 70% or less, still more preferably 60% or less, Most preferably, it is 50% or less.
[0108]
When used in sanitary goods, it is impractical for the water-absorbing resin to decompose during use, so the addition of a chelating agent is necessary. The chelating agent may be added at any stage of the production process of the water absorbent resin. When the amount is 10 ppm or less, the effect is poor, and preferably 20 ppm or more.
[0109]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In the examples, “parts” represents “parts by weight” unless otherwise specified.
[0110]
[Measurement of absorption capacity under no load (GV)]
0.2 g of the water absorbent resin was uniformly placed in a non-woven bag (60 mm × 60 mm) and immersed in a 0.9 wt% aqueous sodium chloride solution (physiological saline). After 30 minutes, the bag is pulled up and 250 × 9.81 m / s using a centrifuge.²After draining for 3 minutes at (250 G), the weight W1 (g) of the bag was measured. Further, the same operation was performed without using the water absorbent resin, and the weight W0 (g) at that time was measured. From these weights W1 and W0,
[0111]
[Expression 1]

[0112]
The GV (absorption capacity under no load) was calculated according to
[0113]
In addition, GV measurement of the water-containing polymer was performed in the same manner as in the case of the water-absorbent resin except that the solid content was 0.2 g, the immersion time in physiological saline was 24 hours, and the solid content was corrected when calculating the GV. It was.
[0114]
[Measurement of soluble content and neutralization rate]
Weigh 184.3 g of 0.9 wt% NaCl aqueous solution (saline) in a plastic container with a lid of 250 ml capacity, add 1.00 g of water-absorbing resin to the aqueous solution, and stir for 16 hours. The amount of solute was extracted. 50.0 g of the filtrate obtained by filtering this extract using filter paper was measured and used as the measurement solution.
[0115]
First, the physiological saline alone was titrated with a 0.1N NaOH aqueous solution to pH 10 and then titrated with a 0.1N HCl aqueous solution to pH 2.7 to obtain an empty titration ([bNaOH] ml, [bHCl] ml).
[0116]
The titration ([NaOH] ml, [HCl] ml) was determined by performing the same titration operation on the measurement solution.
[0117]
For example, in the case of a water-absorbing resin comprising acrylic acid and its sodium salt, based on the weight average molecular weight and the titration amount obtained by the above operation, the soluble amount in the water-absorbing resin and the neutralization rate are calculated as follows: Can be calculated.
[0118]
[Expression 2]

[0119]
In the case of a water-absorbing resin, the soluble content of the water-containing polymer is measured except that the solid content is 1.00 g, the immersion time in physiological saline is 24 hours, and the solid content is corrected when the soluble content is calculated. As well as.
[0120]
[GEX value]
When the GV value of the base polymer is represented by y (g / g) and the soluble content is represented by x (% by weight), the GEX value is defined by the following formula.
[0121]
GEX value = (y−15) / ln (x)
ln (x): natural logarithm of x
The GEX value is used to express an evaluation that it is good that the soluble amount is small with respect to the GV value and that the large amount is inferior with one parameter in the relationship between the GV value and the soluble amount. The higher the value, the higher the performance.
[0122]
[Measurement of residual monomer]
After adding 0.5 g of water-absorbing resin to 1000 g of deionized water and extracting with stirring for 2 hours, the swollen gelled water-absorbing resin was filtered off using filter paper, and the amount of residual monomer in the filtrate was determined by liquid chromatography. analyzed. On the other hand, a calibration curve obtained by analyzing a monomer standard solution having a known concentration in the same manner was used as an external standard, and the amount of residual monomer in the water-absorbent resin was determined in consideration of the dilution rate of the filtrate.
[0123]
In the measurement of the residual monomer of the water-containing polymer, the same as in the case of the water-absorbent resin, except that the solid content is 0.5 g, the immersion time in deionized water is 24 hours, and the solid content is corrected when calculating the residual monomer. Went to.
[0124]
[Measurement of solid content concentration of hydrous polymer]
A small amount of the water-containing polymer taken out from the polymerization vessel was cut out and quickly cooled, and 5 g of the water-containing polymer quickly broken into pieces with scissors was taken in a petri dish and dried for 24 hours in a 180 ° C. dryer. The solid content concentration of the particulate hydropolymer was calculated by taking 5 g of a sample in a petri dish and drying it in a 180 ° C. dryer for 24 hours.
[0125]
[Calculation of concentration ratio]
It is a ratio (concentration ratio) between the solid content concentration of the hydropolymer produced by polymerization and the solid content concentration in the monomer aqueous solution. Here, the solid content in the monomer aqueous solution is a monomer and other additives, and does not include water or a solvent. For example, when the solid content concentration in the monomer aqueous solution is 40% by weight and the solid content concentration of the produced hydropolymer is 48% by weight, the concentration ratio = 48/40 = 1.20.
[0126]
[Measurement of absorption capacity under pressure (AAP)]
0.9 g of water-absorbing resin is evenly sprayed on the bottom net of a plastic support cylinder with an inner diameter of 60 mm in which a stainless steel 400 mesh wire mesh (mesh size 38 μm) is fused to the bottom, and the water-absorbing property is further spread on it. 20g / cm for resin²The total weight was adjusted to 565 g so that a load (corresponding to 1.96 kPa) could be applied uniformly, the outer diameter was slightly smaller than 60 mm, and no gap was formed between the walls of the support cylinder and A piston and a load that are not hindered are placed in this order, and the weight of this measuring device set is measured (Wa).
[0127]
A glass filter with a diameter of 90 mm is placed inside a petri dish with a diameter of 150 mm, and an aqueous 0.9 wt% NaCl solution is added to the same level as the surface of the glass filter. A filter paper having a diameter of 90 mm is placed thereon so that the entire surface is wetted, and excess liquid is removed.
[0128]
The measuring device set is placed on the wet filter paper and the liquid is absorbed under load. After 1 hour, the measuring device set is lifted and removed, and its weight is measured again (Wb).
[0129]
The absorption capacity (AAP) under pressure is expressed by the following formula:
[0130]
[Equation 3]

[0131]
Is required.
[0132]
[Measurement of temperature of polymerization system]
In order to measure the temperature of the system with a rapid temperature change, a PC card type data acquisition system NR-1000 manufactured by Keyence Co., Ltd. was used, and a thermocouple was placed at the center of the polymerization system, and a sampling period of 0.1 Measured in seconds. From the obtained temperature-time chart, the polymerization initiation temperature and peak temperature (maximum temperature reached) were read.
[0133]
[Polymerization time]
When the monomer aqueous solution is placed in the polymerization vessel and the conditions for initiating the polymerization are complete (when using a photodegradable initiator, when the light irradiation starts, when not using a photodegradable initiator, the monomer aqueous solution and The time from when the polymerization initiator is put into the polymerization vessel to the peak temperature is measured. That is, (induction period) + (time from the start of polymerization to the peak temperature) is measured.
[0134]
[Polymerization temperature rise ratio]
The polymerization temperature rise ratio is the ratio of ΔT (difference between the highest temperature reached during polymerization and the polymerization initiation temperature, ° C.) observed in the polymerization system and the theoretical ΔT (° C.). That is,
Polymerization temperature rise ratio = (observed ΔT (° C.)) / (Theoretical ΔT (° C.))
Here, theoretical ΔT (° C.) = (Monomer mol) × (1.85 kcal / mol) / (solid content in monomer aqueous solution (kg) × 0.5 (kcal / ° C./kg)+single amount Water in body aqueous solution (kg) x 1.0 (kcal / ° C / kg))
[Measurement of dissolved oxygen content of monomer aqueous solution]
Using a measuring device (DOMETER UD-1 type manufactured by Central Science Co., Ltd.), the prepared monomer aqueous solution is cooled in ice in a nitrogen atmosphere while gently stirring so as not to engulf bubbles. Was measured for the amount of dissolved oxygen at 50 ° C.
[0135]
[Increased neutralization rate]
The difference between the neutralization rate of the pace polymer and the neutralization rate of the monomer is expressed in points. For example, when the neutralization rate of the pace polymer is 65 mol% and the neutralization rate of the monomer is 60 mol%, the neutralization rate increase is 5 points.
[0136]
[Measurement of expansion ratio during polymerization]
Since water boils during polymerization, the polymerization system may expand. A scale in units of cm is provided in the polymerization vessel in the vertical and horizontal directions, the size when it is expanded most during polymerization is visually measured, its volume is determined, and the ratio to the volume of the monomer aqueous solution is calculated. That is,
Expansion ratio during polymerization (times) = maximum volume of polymerization system / volume of aqueous monomer solution
[Measurement of particle size distribution of particulate hydropolymer]
After putting about 300 g of the particulate hydropolymer into a plastic bag, add 1 g of Aerosil R-972 (manufactured by Nippon Aerosil Co., Ltd., hydrophobic fine particle silicon oxide), mix by hand, and dissolve well. . The solution is shaken for 10 minutes using a standard sieve having an inner diameter of 20 cm and a Ro-Tap type sieve shaker.
[0137]
Depending on the moisture content of the particulate water-containing polymer, it may be difficult to measure the exact particle size distribution by agglomeration when shaking, so measurement is performed while adding Aerosil R-972 to prevent reaggregation.
[0138]
[Solubilization test method]
The water-absorbent resin basically has a form of a crosslinked body in which a water-soluble polymer is crosslinked. This solubilization test method is a test method for checking the ease of decomposition of the water-absorbent resin when exposed to the decomposition conditions. Therefore, the trend does not always agree with this test method depending on the degradation conditions actually exposed.
[0139]
In this test method, the soluble components and the like are washed away by washing with water to obtain a gel composed of the crosslinked body itself, and decomposed by irradiating it with ultraviolet rays. This evaluation method provides a quantitative index of the ease of decomposing the crosslinked body itself. The procedure is shown below.
1. The water-absorbing resin is classified, and those having a size of 300 μm to 850 μm are collected.
2. 0.500 g of the aliquot is dispersed and swollen in 1000 cc ion-exchanged water in a cylindrical container made of PP (polypropylene). At this time, it is carried out while stirring with a magnetic stirrer (600 rpm).
3. Continue stirring at room temperature for 2 hours.
4). This dispersion is applied to a 20 cm diameter circular standard sieve (aperture 300 μm). Water is drained while tapping the sieve by hand, the gel remaining on the sieve is returned again into the cylindrical container made of PP, ion exchanged water is added to make the total amount 1000 cc, and stirring is performed again for 2 hours.
5. This washing operation is performed three times, and the drained gel is placed in a glass petri dish having a diameter of 153 mm.
6). A mercury lamp H400BL (manufactured by Toshiba Lighting & Technology Co., Ltd.) is attached to the reflective shade SN-4042A (manufactured by Toshiba Lighting & Technology Co., Ltd.). Place a petri dish on the surface 18 cm below. When the irradiation energy is measured at 18 cm directly under the mercury lamp using an ultraviolet ray integrating light meter UIT-150 (manufactured by Ushio Electric Co., Ltd.), it is 40 mW / cm 2.
7). Irradiate the gel on the petri dish with a mercury lamp for 30 minutes.
8). The petri dish contents after irradiation are returned to a PP cylindrical container, and ion exchange water is added to make the total amount 1000 cc, and stirring is performed for 2 hours. Washing is performed 3 times by performing the same operation as in 4 and 5 above.
9. The gel remaining on the standard sieve (aperture 300 μm) is placed in a glass petri dish with a diameter of 153 mm and dried in a 180 ° C. drier for 5 hours to obtain the solid content (a).
10. Separately, for the gel (before UV irradiation) obtained by performing the above operations 1 to 5, the solid content (b) is obtained in the same manner as 9 above.
11. The solubilization residual rate is calculated by the solubilization residual rate = a / b × 100 (%).
[0140]
Example 1
A stainless steel beaker having an inner diameter of 10 cm was fitted with a foamed polystyrene lid equipped with a nitrogen introduction pipe, an exhaust pipe, and a thermometer, and the entire stainless steel beaker was wrapped with foamed polystyrene as a heat insulating material. 40.6 g of an 80 wt% aqueous solution of acrylic acid in which 0.09 g of polyethylene glycol diacrylate (number average molecular weight 478) was dissolved was added, and 28.2 g of 48 wt% aqueous solution of sodium hydroxide was stirred with a magnetic stirrer. What was diluted with 31.0g was added and neutralized. The internal temperature was 90 ° C. The neutralization rate of this monomer aqueous solution is 75 mol%. While introducing nitrogen, 0.45 g of a 10% by weight aqueous solution of sodium persulfate was added thereto. As a result, polymerization started rapidly (polymerization start temperature 90 ° C.), and while generating water vapor, the polymerization peak temperature (108 ° C.) Reached. The time required from the addition of the sodium persulfate aqueous solution to the polymerization peak temperature, that is, the polymerization time was 2 minutes. After the polymerization peak temperature was reached, the temperature was maintained for 5 minutes, and the water-containing polymer was taken out and fragmented with scissors. It took 7 minutes from the addition of the polymerization initiator to the removal of the water-containing polymer. The finely divided water-containing polymer was dried with a hot air dryer at 170 ° C. for 40 minutes, and then pulverized with a desktop pulverizer. Subsequently, the pulverized product was classified with a sieve screen having openings of 600 μm and 300 μm, so that a base polymer (1) having a particle size of 300 to 600 μm was obtained.
[0141]
The GV of the base polymer (1) was 47 g / g, the soluble content was 10% by weight, the residual monomer was 300 ppm, and the neutralization rate was 77 mol%. The solid content concentration of the finely divided hydropolymer was 48% by weight. The concentration ratio was 1.20.
Subsequently, 100 parts of the base polymer (1) was mixed with a surface cross-linking agent composition liquid consisting of 0.05 part of ethylene glycol diglycidyl ether, 1 part of propylene glycol, and 2 parts of water, and the resulting mixture was heated to 80 ° C. A surface-crosslinked water-absorbing resin (1) having a crosslinked surface was obtained by heat treatment in a dryer for 40 minutes.
[0142]
The surface cross-linked water-absorbent resin (1) had a GV of 39 g / g and an AAP of 38 g / g.
[0143]
The results are shown in Table 1.
[0144]
Moreover, the side view photograph of the water-containing polymer obtained in Example 1 is shown in FIG. The horizontal bar in the lower center of the photograph in FIG. 2 is 1 cm in length.
[0145]
-Comparative Example 1-
In the same stainless steel beaker as used in Example 1, a polymerization apparatus equipped with a nitrogen-introducing pipe, an exhaust pipe and a thermometer-equipped styrene foam lid was immersed in a 20 ° C. water bath. The same monomer aqueous solution was added and 0.45 g of a 10 wt% aqueous solution of sodium persulfate and 0.45 g of a 0.1 wt% L-ascorbic acid aqueous solution were added while introducing nitrogen. Polymerization started after 7 minutes. Polymerization was performed while cooling in a 20 ° C. water bath, and the peak temperature reached 60 ° C. Thereafter, the water bath was switched to 70 ° C. and heated for 30 minutes.
[0146]
Thereafter, the water-containing polymer was taken out and fragmented with scissors. It took 62 minutes from the addition of the polymerization initiator system to the removal of the water-containing polymer. The finely divided water-containing polymer was dried with a hot air dryer at 170 ° C. for 40 minutes, and then pulverized with a desktop pulverizer. Subsequently, the pulverized product was classified with a sieve screen having openings of 600 μm and 300 μm to obtain a comparative base polymer (1) having a particle size of 300 to 600 μm.
[0147]
The comparative base polymer (1) had a GV of 36 g / g, a soluble content of 11 wt%, a residual monomer of 300 ppm, and a neutralization rate of 75 mol%. Further, the solid content concentration of the finely divided hydropolymer was 42% by weight. The concentration ratio was 1.05.
[0148]
Next, 100 parts of the comparative base polymer (1) was mixed with 0.05 part of ethylene glycol diglycidyl ether, 1 part of propylene glycol and 2 parts of water, and the resulting mixture was mixed at 80 ° C. A comparative surface-crosslinked water-absorbing resin (1) having a crosslinked surface was obtained by heat treatment for 40 minutes in a dryer.
[0149]
The comparative surface crosslinked water-absorbing resin (1) had a GV of 28 g / g and an AAP of 26 g / g.
[0150]
The results are shown in Table 1.
[0151]
Example 1 and Comparative Example 1 have the same monomer composition, initiator amount, and the like, except that the polymerization initiation temperature (90 ° C. in Example 1, 20 ° C. in Comparative Example 1) and the subsequent temperature are different. is there. The performance of the obtained base polymer and water-absorbent resin is superior in Example 1. The reason for this is not clear, but the present inventors' estimation is as follows.
[0152]
At the start of polymerization at 20 ° C., the polymer produced at a low polymerization rate is too high in molecular weight, and a large amount of crosslinking agent is consumed in the initial stage of polymerization, leading to a decrease in GV (references; Polymerization at 90 ° C. for polymerization at Crosslinker Reactivity and the Structure of Superabsorbent Gels, DJ Arriola et al., J. Appl. Polym. Sci. 63, 439-451 (1997)) Since the molecular weight of the polymer produced at a low stage is suppressed, it is considered that the decrease in GV is suppressed.
[0153]
-Example 2-
83.5 parts of acrylic acid, 62.1 parts of 48.5% by weight NaOH aqueous solution, 54.3 parts of ion-exchanged water, 0.11 part of polyethylene glycol diacrylate (number average degree of polymerization of ethylene oxide = 8) as a crosslinking agent , And 0.01 parts of 2-hydroxy-2-methyl-1-phenyl-propan-1-one as an initiator to mix a monomer concentration of 50 wt% and a neutralization rate of 65 mol% An aqueous solution was created. This solution was degassed for 30 minutes under a nitrogen gas atmosphere, and then placed on a 90 ° C. hot plate (NEO HOTPLATE HI-1000 manufactured by Inei Seieido Co., Ltd.), and a bottom surface 200 × 260 mm Teflon into which nitrogen gas was introduced. Poured into a coated stainless steel container. When the aqueous monomer solution is heated to 60 ° C., it is irradiated with ultraviolet rays for 10 minutes using a black light fluorescent lamp (four FL6BLBs manufactured by Toshiba Lighting & Technology Co., Ltd.) (light quantity 900 mJ / cm).²), A hydrous polymer having a thickness of about 3 mm was obtained. The polymerization initiation temperature was 60 ° C., the maximum temperature during the polymerization was 110 ° C., the polymerization time was 80 seconds, and the expansion ratio was 5 times. Immediately after the ultraviolet irradiation, the water-containing polymer was taken out, chopped with scissors, dried with hot air at 170 ° C. for 30 minutes, and pulverized with a table pulverizer. Subsequently, the pulverized product was classified with a sieve screen having openings of 600 μm and 300 μm to obtain a base polymer (2) having a particle diameter of 300 to 600 μm.
[0154]
The base polymer (2) had a GV of 58 g / g, a soluble content of 16 wt%, a neutralization rate of 68 mol%, and a residual monomer content of 2200 ppm. The solid content concentration of the hydropolymer was 60% by weight, and the concentration ratio was 1.20.
[0155]
Next, 100 parts of the base polymer (2) was mixed with 0.05 part of ethylene glycol diglycidyl ether, 1 part of propylene glycol and 2 parts of water, and the resulting mixture was mixed at 80 ° C. A surface-crosslinked water-absorbing resin (2) having a crosslinked surface was obtained by heat treatment in a dryer for 40 minutes.
[0156]
The surface-crosslinked water-absorbent resin (2) had a GV of 42 (g / g) and an AAP of 36 (g / g).
[0157]
The results are shown in Table 1.
[0158]
Example 3
Solution (A) in which 139.5 g of acrylic acid, 0.09 g of polyethylene glycol diacrylate (number average molecular weight 478), and 0.02 g of 2-hydroxy-2-methyl-1-phenyl-propan-1-one were mixed, 48 Then, 55.8% NaOH aqueous solution 95.8g was diluted with ion-exchanged water 61.2g, and diethylenetriamine pentaacetic acid / pentasodium 0.02g was added to prepare NaOH aqueous solution (B). Degassed for a minute. While stirring with a magnetic stirrer, (A) was added to (B) at once in an open system and mixed. Precipitates are observed at the beginning of mixing, but dissolve immediately and the temperature of the solution rises to about 90 ° C. due to heat of neutralization and heat of dissolution (monomer concentration 55 wt%, neutralization rate 60 mol%) was gotten. Further, 0.58 g of 10% by weight sodium persulfate aqueous solution was added to this monomer aqueous solution and stirred for several seconds. Immediately after that, it was placed on a 90 ° C. hot plate, and a bottom surface 200 × 260 mm stainless steel with a silicon sheet attached to the inner surface It was poured in an open system into a bat-shaped container (surface temperature: about 64 ° C.) (solution thickness: about 5 mm). The stainless bat-shaped container has a bottom surface of 200 × 260 mm, a top surface of 560 × 460 mm, and a height of 140 mm, a central cross section that is trapezoidal, and an open top surface. Immediately thereafter, ultraviolet light was irradiated with a black light mercury lamp (peak wavelength: 352 nm, type H400BL, mounted in the projector MT-4020, both lamp and projector manufactured by Toshiba Lighting & Technology Co., Ltd.) to initiate polymerization. Polymerization proceeded while generating water vapor and expanding and foaming vertically and horizontally, and then contracted to the same extent as the original size. As a result of visual estimation, the hydrated polymer expanded and contracted to a maximum of about 30 times the volume of the aqueous monomer solution. When the water-containing polymer expands, the thin water-containing polymer crawls up the inclined portion on the side surface of the container. When the water-containing polymer shrinks, the water-containing polymer returns to its original direction but becomes a water-containing polymer larger than the bottom surface size and stops moving. This expansion and contraction was completed within about 1 minute, and the water-containing polymer was taken out when UV irradiation was performed for 2 minutes. From the record of the temperature change of the polymerization system, it was read that the polymerization initiation temperature was 88 ° C. and the maximum temperature reached 111 ° C. The obtained water-containing polymer was in a crushed state as it was, although it depended on the size of the bubbles, and had a lot of wrinkles. This water-containing polymer was pulverized with a vertical crusher (model VM27-S, manufactured by Orient Co., Ltd., screen diameter: 8 mm) to obtain a fluid particulate water-containing polymer (3).
[0159]
The hydropolymer (3) had a GV of 33 g / g, a soluble content of 6% by weight, a residual monomer content of 600 ppm, a solid content concentration of 70% by weight, and a concentration ratio of 1.27.
[0160]
Subsequently, the hydropolymer (3) was dried with hot air at 170 ° C. for 20 minutes, and the dried product was pulverized using a roll mill. Subsequently, the pulverized product was classified with a sieve mesh having an opening of 850 μm and 150 μm to obtain a base polymer (3) having a particle diameter of 150 to 850 μm mostly and a weight average particle diameter of 360 μm.
[0161]
The GV of the base polymer (3) was 48 (g / g), the soluble content was 24 wt%, the neutralization rate was 65 mol%, and the residual monomer was 200 ppm. In addition, when the particles of the base polymer (3) were observed with a microscope, most of the particles were amorphous without bubbles because the bubble size was relatively large even though the polymerization was accompanied by foaming. It was.
[0162]
Then, 100 parts of the base polymer (3) was mixed with 0.03 part of ethylene glycol diglycidyl ether, 1 part of propylene glycol, and 5 parts of water, and the resulting mixture was put into a sealed container. The surface-crosslinked water-absorbing resin (3) whose surface was crosslinked was obtained by heat treatment in an oven at 80 ° C. for 1 hour.
The surface crosslinked water-absorbing resin (3) had a GV of 34 g / g and an AAP of 35 g / g.
Further, 100 parts of the base polymer (3) was mixed with 0.03 part of ethylene glycol diglycidyl ether, 1 part of propylene glycol, 3 parts of water and 0.9 part of isopropyl alcohol to obtain The obtained mixture was heat-treated in a container heated in an oil bath at 170 ° C. for 20 minutes to obtain a surface-crosslinked water-absorbing resin (3a) whose surface was crosslinked.
[0163]
The surface-crosslinked water-absorbent resin (3a) had a GV of 34 g / g and an AAP of 35 g / g.
[0164]
The results are shown in Table 1.
[0165]
Moreover, the side surface photograph of the water-containing polymer obtained in Example 3 is shown in FIG. 3, the top surface photograph is shown in FIG. 4, and the bottom surface photograph is shown in FIG. The horizontal bar at the bottom center of the photographs in FIGS. 3, 4 and 5 has a length of 1 cm.
[0166]
Example 4
Polymerization was carried out in the same manner as in Example 3, and the evaporated water vapor was guided to a condenser cooled with ice water using a fan and collected. The aqueous solution collected by performing this operation twice was 60 g, of which 3.4% by weight of acrylic acid was contained.
[0167]
The same operation as in Example 3 was performed except that this recovered water containing acrylic acid was used in place of most of the ion-exchanged water of Example 3. The physical property values of the obtained base polymer (4) are shown in Table 1.
[0168]
-Example 5
In Example 3, the same procedure as in Example 3 was performed except that 0.14 g of trimethylolpropane triacrylate (molecular weight 296) was used instead of 0.09 g of the crosslinking agent polyethylene glycol diacrylate (number average molecular weight 478). A base polymer (5) was obtained. A surface crosslinker composition liquid composed of 1 part of propylene glycol, 0.5 part of 1,4 butanediol, 3 parts of water and 1 part of isopropyl alcohol was mixed with 100 parts of the obtained base polymer (5). The said mixture was heat-processed at 210 degreeC for 40 minute (s), and surface crosslinked water-absorbing resin (5) was obtained.
[0169]
The results are shown in Table 1.
[0170]
Moreover, the side surface photograph of the water-containing polymer obtained in Example 5 is shown in FIG. The horizontal bar at the lower center of the photograph in FIG. 6 is 1 cm in length.
[0171]
-Example 6
To 100 parts of the base polymer (5) obtained in Example 5, a surface cross-linking agent composition liquid consisting of 3 parts of ethylene carbonate, 3 parts of water and 1 part of isopropyl alcohol was mixed. The said mixture was heat-processed at 210 degreeC for 40 minute (s), and surface crosslinked water-absorbing resin (6) was obtained.
[0172]
The results are shown in Table 1.
[0173]
[Table 1]

[0174]
-Examples 7 to 10-
Except that the polymerization initiation temperature was changed by adjusting the temperature of the aqueous monomer solution and the hot plate temperature, the polymerization and the subsequent operations were carried out in the same manner as in Example 3, and the base polymers of Examples 7 to 10 (base polymer) (7) to (10)) were obtained. The results are summarized in Table 2.
[0175]
Moreover, the side view photograph of the water-containing polymer obtained in Example 7 is shown in FIG. Moreover, the photograph of the gel which a part of the water-containing polymer of Example 7 was cut out and swollen with tap water is shown in FIG. In the photograph of FIG. 8, the water-containing polymer outside the petri dish is a section similar to a cut-out section of the water-containing polymer before swelling with tap water. The vertical bar at the lower left of the photographs in FIGS. 7 and 8 is 1 cm long.
[0176]
[Table 2]

[0177]
Moreover, about the base polymer of Example 3 and Examples 7-10, the graph showing the relationship between polymerization reaction temperature and time was shown in FIG.
[0178]
In Examples 7 to 10, the same monomer composition was used, and the polymerization initiation temperature was simply changed to 88 ° C, 73 ° C, 60 ° C, and 44 ° C. The higher the starting temperature, the better the performance of the pace polymer and the higher the solid content concentration of the hydropolymer. The peak temperature is lower as the starting temperature is higher. The reason for such a phenomenon is not clear, but the present inventors' inference is as follows.
[0179]
When the polymerization start temperature is low, a hard water-containing polymer is produced from the start until the boiling is reached, so that the boiling temperature is high, that is, the peak temperature is high, and the bursting noise is large. When the polymerization start temperature is high, a hard hydrous polymer is not formed from the start until boiling reaches, the monomer aqueous solution with high viscosity foams greatly with boiling, the surface area increases, water vapor evaporates well, the peak temperature is It is suppressed and the solid content concentration becomes high. There is almost no plosive sound.
[0180]
-Comparative Example 2-
72.1 g of acrylic acid was added to 22.2 g of ion-exchanged water, 49.5 g of potassium hydroxide having a purity of 85% as a neutralizing agent, and 0.01 g of N, N′-methylenebisacrylamide as a divinyl compound. Were sequentially added to prepare a potassium acrylate solution (neutralization rate 75 mol%) having a mixed monomer concentration of 70% by weight.
[0181]
The aqueous solution prepared above was kept at 70 ° C., and 2.9 g of 18% by weight aqueous solution of ammonium persulfate (total weight of potassium acrylate, free acrylic acid and N, N′-methylenebisacrylamide (monomer component) 0.5 wt%) with respect to the total weight) and 1.7 g (0.5 wt%) of a 30.6 wt% aqueous solution of sodium hydrogen sulfite are mixed, and the mixed solution is put into a stainless steel beaker (capacity 2 L, φ135 mm). Then, it became a layer of about 10 mm thickness. After about 7 seconds, the polymerization reaction was started and the reaction was completed in about 1 minute, during which the maximum temperature was 145 ° C.
The obtained water-containing polymer was solid and could be easily pulverized, and a comparative base polymer (2) was obtained. The solid content was 89% by weight, GV was 23 g / g, the soluble content was 50% by weight, the neutralization rate was 77 mol%, and the residual monomer was 5900 ppm.
[0182]
The results are summarized in Table 2.
[0183]
This comparative example traces Example 1 of JP-A-58-71907 (Arakawa Chemical). It can be seen that when the solid content concentration is up to 89% by weight, the amount of soluble component is remarkably increased.
[0184]
-Example 11-
Solution (A) in which 139.5 g of acrylic acid, 0.09 g of polyethylene glycol diacrylate (number average molecular weight 478), and 0.02 g of 2-hydroxy-2-methyl-1-phenyl-propan-1-one were mixed, 48 55.8% NaOH aqueous solution 95.8g was diluted with ion-exchanged water 64.1g, and diethylenetriaminepentaacetic acid / sodium sodium 0.02g was added to prepare NaOH aqueous solution (B) for 30 minutes under nitrogen gas atmosphere. I was degassed. While stirring with a magnetic stirrer, (A) was added to (B) at once in an open system and mixed. Precipitates are observed at the beginning of mixing, but dissolve immediately, and the temperature of the solution rises to about 85 ° C. due to heat of neutralization and heat of dissolution (monomer concentration 55 wt%, neutralization rate 60 mol%) was gotten. Further, 0.58 g of 10% by weight sodium persulfate aqueous solution was added to this monomer aqueous solution and stirred for several seconds. Immediately after that, it was placed on a 90 ° C. hot plate, and a bottom surface 200 × 260 mm stainless steel with a silicon sheet attached to the inner surface It was poured in an open system into a bat-shaped container (surface temperature: about 64 ° C.) (solution thickness: about 5 mm). The stainless bat-shaped container has a bottom surface of 200 × 260 mm, a top surface of 560 × 460 mm, and a height of 140 mm, a central cross section that is trapezoidal, and an open top surface. Immediately thereafter, UV irradiation was performed with a black light mercury lamp (peak wavelength: 352 nm, type H400BL, manufactured by Toshiba Lighting & Technology Co., Ltd.) to initiate polymerization. Polymerization proceeded while generating water vapor and expanding and foaming vertically and horizontally, and then contracted to the same extent as the original size. As a result of visual estimation, the hydrated polymer expanded and contracted to a maximum of about 30 times the volume of the aqueous monomer solution. When the water-containing polymer expands, the thin water-containing polymer crawls up the inclined portion on the side surface of the container. When the water-containing polymer shrinks, the water-containing polymer returns to its original direction but becomes a water-containing polymer larger than the bottom surface size and stops moving. This expansion and contraction was completed within about 1 minute, and the water-containing polymer was taken out when UV irradiation was performed for 2 minutes. From the temperature measurement chart, the polymerization initiation temperature was read as 82 ° C., and the maximum temperature reached as 113 ° C. The obtained water-containing polymer (11) was a form with much soot, and solid content concentration was 70 weight%. Therefore, the concentration ratio was 1.27. This hydropolymer (11) was pulverized with a vertical pulverizer (type VM27-S, screen diameter 3 mm, manufactured by Orient Co., Ltd.) to obtain a fluid particulate hydropolymer (11).
[0185]
The weight average particle diameter of the particulate hydropolymer (11) was 1 mm, GV was 33 g / g, the soluble content was 6 wt%, the residual monomer was 600 ppm, and the solid content concentration was 71 wt%.
[0186]
Subsequently, the particulate hydropolymer (11) was subjected to hot air drying for 20 minutes in a drier at 170 ° C., and the dried product was pulverized using a roll mill. Subsequently, the pulverized product was classified with a sieve mesh having an opening of 850 μm and 150 μm, whereby a base polymer (11) having a particle size of 150 to 850 μm and a weight average particle size of 360 μm was obtained.
[0187]
GV of the base polymer (11) was 48 g / g, the soluble content was 24 wt%, the neutralization rate was 65 mol%, and the residual monomer was 200 ppm. Moreover, when the particles of the base polymer (11) were observed with a microscope, most of the particles were amorphous without bubbles because the bubble size was relatively large even though the polymerization was accompanied by foaming. It was.
[0188]
Then, 100 parts of the base polymer (11) was mixed with 0.03 part of ethylene glycol diglycidyl ether, 1 part of propylene glycol, and 5 parts of water, and the resulting mixture was put into a sealed container. The surface-crosslinked water-absorbent resin (11) whose surface was cross-linked was obtained by heat treatment in a dryer at 80 ° C. for 1 hour.
[0189]
The surface-crosslinked water-absorbent resin (11) had a GV of 34 g / g and an AAP of 32 g / g.
[0190]
Further, 100 parts of the base polymer (11) was mixed with 0.03 part of ethylene glycol diglycidyl ether, 1 part of propylene glycol, 3 parts of water and 0.9 part of isopropyl alcohol to obtain The obtained mixture was heat-treated in a container heated by an oil bath at 170 ° C. for 20 minutes to obtain a surface-crosslinked water-absorbing resin (11a) having a crosslinked surface.
[0191]
The surface-crosslinked water-absorbent resin (11a) had a GV of 34 g / g and an AAP of 35 g / g.
[0192]
-Example 12-
Solution (A) in which 308.2 g of acrylic acid, 0.20 g of polyethylene glycol diacrylate (number average molecular weight 478), and 0.04 g of 2-hydroxy-2-methyl-1-phenyl-propan-1-one were mixed, 48 Prepare NaOH aqueous solution (B) by diluting 194.1 g of 5 wt% NaOH aqueous solution with 97.0 g of ion-exchanged water, and add (A) to (B) at a stretch in an open system while stirring with a magnetic stirrer. did. Precipitates were observed at the beginning of mixing, but dissolved immediately, and an aqueous monomer solution (monomer concentration 60 wt%, neutralization rate 55 mol%, temperature 102 ° C.) was obtained. (This monomer aqueous solution preparation operation was performed in another batch in the same manner, and the amount of dissolved oxygen was measured and found to be 0.7 ppm.) Further, 10% by weight of sodium persulfate aqueous solution 1.3 g was added to this monomer aqueous solution. The mixture was stirred for several seconds and immediately placed on a 90 ° C. hot plate and poured into an open system into a stainless steel bat-type container with a silicon sheet attached to the inner surface. The stainless bat-shaped container has a bottom surface of 200 × 260 mm, a top surface of 560 × 460 mm, and a height of 140 mm, a central cross section that is trapezoidal, and an open top surface. Immediately thereafter, UV irradiation was performed with a black light mercury lamp (peak wavelength: 352 nm, type H400BL, manufactured by Toshiba Lighting & Technology Co., Ltd.) to initiate polymerization. Polymerization proceeded while generating water vapor and expanding and foaming vertically and horizontally (expansion ratio was 40 times). When UV irradiation was performed for 2 minutes, the hydropolymer was taken out. The solid content concentration of this water-containing polymer was 77% by weight. This water-containing polymer is pulverized with a vertical pulverizer (model VM27-S, screen diameter 3 mm, manufactured by Orient Co., Ltd.) using a screen having a pore diameter of 1 mm to obtain a fluid particulate water-containing polymer. It was. Subsequently, this particulate hydropolymer was classified with a sieve having openings of 850 μm and 150 μm to obtain a particulate hydropolymer (12) having a weight average particle diameter of 500 μm.
[0193]
The particulate hydropolymer (12) has a GV of 22 g / g, a soluble content of 2% by weight, a residual monomer of 600 ppm, and a solid content of 79% by weight.
[0194]
-Example 13-
Solution (A) in which 279.0 g of acrylic acid, 0.09 g of polyethylene glycol diacrylate (number average molecular weight 478), and 0.03 g of 2-hydroxy-2-methyl-1-phenyl-propan-1-one were mixed, 48 A NaOH aqueous solution (B) was prepared by diluting 191.54 g of a 5 wt% NaOH aqueous solution with 128.2 g of ion-exchanged water. While stirring with a magnetic stirrer, (A) was added to (B) at once in an open system and mixed. Precipitates were observed at the beginning of mixing, but dissolved immediately, and an aqueous monomer solution (monomer concentration 55 wt%, neutralization rate 60 mol%, temperature 92 ° C.) was obtained. (This monomer aqueous solution adjustment operation was carried out in a separate batch in the same manner, and the amount of dissolved oxygen was measured to be 1.4 ppm.) Furthermore, 1.3 g of 10% by weight sodium persulfate aqueous solution was added to this monomer aqueous solution. The mixture was stirred for several seconds and immediately placed on a 90 ° C. hot plate and poured into an open system into a stainless steel bat-type container with a silicon sheet attached to the inner surface. The stainless bat-shaped container has a bottom surface of 200 × 260 mm, a top surface of 560 × 460 mm, and a height of 140 mm, a central cross section that is trapezoidal, and an open top surface. Immediately thereafter, UV irradiation was performed with a black light mercury lamp (peak wavelength: 352 nm, type H400BL, manufactured by Toshiba Lighting & Technology Co., Ltd.) to initiate polymerization. Polymerization proceeded while generating water vapor and expanding and foaming vertically and horizontally (expansion ratio was 35 times). When UV irradiation was performed for 2 minutes, the water-containing polymer was taken out (solid content concentration was 69% by weight). The water-containing polymer is first pulverized with a vertical pulverizer (model VM27-S, manufactured by Orient Co., Ltd.) using a screen with a pore size of 3 mm, and the pulverized product is further pulverized with a screen with a pore size of 1 mm. By doing so, a fluid particulate water-containing polymer was obtained. Subsequently, the particulate hydropolymer was classified with a sieve having openings of 850 μm and 150 μm to obtain a particulate hydropolymer (13) having a weight average particle size of 610 μm (solid content concentration is 70% by weight).
[0195]
The particulate hydropolymer (13) had a GV of 34 g / g, a soluble content of 10% by weight, and a residual monomer content of 700 ppm.
[0196]
Subsequently, 100 parts of the particulate hydropolymer (13) was mixed with a surface cross-linking agent composition liquid composed of 0.02 part of ethylene glycol diglycidyl ether and 0.2 part of propylene glycol, and the resulting mixture was sealed in a sealed container. In the inside, it heat-processed in the dryer of 80 degreeC for 1 hour. Although the particles after heating once become aggregates, they can be easily crushed into particles by cooling to room temperature, and a surface-crosslinked water-absorbing resin (13) having a crosslinked surface is obtained.
[0197]
The surface-crosslinked water-absorbing resin (13) has a GV of 25 g / g, an AAP of 23 g / g, a residual monomer of 200 ppm, and a solid content concentration of 74% by weight.
[0198]
-Example 14-
One piece of the water-containing polymer (11) having a lot of wrinkles obtained in Example 11 was roughly cut into four pieces by a circular saw, and then a turbo cutter (C-300, manufactured by Turbo Kogyo Co., Ltd.) having a screen diameter of 3 mm. ) And pulverized to obtain a particulate hydrous polymer (14). About 30 kg of the hydropolymer (11) could be processed in 30 minutes.
[0199]
The obtained particulate hydropolymer (14) had a solid content concentration of 71% by weight and a weight average particle size of 1.3 mm. The particle size distribution obtained with a Ro-Tap type sieve shaker was as follows.
9% by weight of particulate hydropolymer with a particle size of 2mm or more
38% by weight of a particulate water-containing polymer having a particle size of 1.4 mm or more and less than 2 mm
31% by weight of particulate water-containing polymer having a particle size of 1 mm or more and less than 1.4 mm
Particulate water-containing polymer having a particle size of 0.5 mm or more and less than 1 mm 19% by weight
3% by weight of particulate water-containing polymer with a particle size of less than 0.5 mm
-Example 15-
The particulate hydropolymer (14) obtained by crushing with the turbo cutter of Example 14 was put into a turbo grinder (TG-300, manufactured by Turbo Kogyo Co., Ltd.) and further pulverized to obtain particulate hydrous weight. Combined (15) was obtained.
Table 4 shows the screen diameter of the turbo grinder, the weight average particle diameter of the pulverized water-containing polymer (15), and the solid content concentration.
[0200]
-Example 16-
Using a fluidized bed dryer (Pulvis GB22, manufactured by Yamato Scientific Co., Ltd.), the particulate hydropolymers (14) and (15) were subjected to an internal temperature of 180 ° C., a material of 100 grams, a hot air flow rate of 0.35 cubic meters / Dried for minutes.
[0201]
The following table shows the material temperature of the particulate hydropolymers (14) and (15) during drying, the solid content concentration after drying, and the dry particulate weight obtained by classifying 300 μm to 600 μm after grinding the dried product. Table 3 shows the measured values of GV, soluble content, and residual monomer of the combined (14) and (15).
[0202]
[Table 3]

[0203]
-Example 17-
One water-containing polymer (11) having a large amount of wrinkles obtained in Example 11 was cut into approximately four pieces with a circular saw, and then turned into a rotoplex (28 / 40Ro, manufactured by Hosokawa Micron Corporation) having a screen diameter of 2 mm. Continuously charged. The throughput was about 70 kg / hour.
[0204]
After pulverization, the particulate hydropolymer (17) obtained by collecting with a cyclone had a solid content concentration of 72% by weight and a weight average particle size of about 1 mm. The particle size distribution of the particulate hydropolymer (17) determined with a Ro-Tap type sieve shaker was as shown below.
1% by weight of particulate hydropolymer with a particle size of 2mm or more
29% by weight of particulate water-containing polymer having a particle size of 1.2 mm or more and less than 2 mm
35% by weight of a particulate hydropolymer having a particle size of 0.85 mm or more and less than 1.2 mm
26% by weight of a particulate hydropolymer having a particle size of 0.3 mm or more and less than 0.85 mm
9% by weight of particulate water-containing polymer with a particle size of less than 0.3 mm
-Example 18-
One piece of the water-containing polymer (11) having a lot of wrinkles obtained in Example 11 was roughly cut into four pieces with a circular saw, and then turned into a rotoplex (28 / 40Ro, manufactured by Hosokawa Micron Corporation) having a screen diameter of 5 mm. Continuously charged. The throughput was about 100 kg / hour.
[0205]
After pulverization, the particulate hydropolymer (18) obtained by collecting with a cyclone had a solid content concentration of 71% by weight and a weight average particle size of 2 mm. The particle size distribution of the particulate hydropolymer (18) determined with a Ro-Tap type sieve shaker was as shown below.
6% by weight of a particulate hydropolymer having a particle size of 2.8 mm or more
Particulate water-containing polymer having a particle size of 1.7 mm or more and less than 2.8 mm 58% by weight
29% by weight of particulate water-containing polymer having a particle size of 0.85 mm or more and less than 1.7 mm
6% by weight of particulate water-containing polymer having a particle size of 0.15 mm or more and less than 0.85 mm
1% by weight of a particulate hydropolymer having a particle size of less than 0.15 mm
Next, the pulverized particulate hydropolymer (18) was put into a dry meister (manufactured by Hosokawa Micron Co., Ltd., an apparatus for simultaneously pulverizing and drying with hot air and a dispersion rotor). At this time, the hot air temperature was 270 ° C., and the dispersion rotor was 3000 rpm.
[0206]
The particle size distribution of the dried hydropolymer (18a) collected by a cyclone and obtained with a Ro-Tap sieve shaker was as shown below.
1% by weight of a particulate hydropolymer having a particle size of 2.8 mm or more
5% by weight of a particulate hydropolymer having a particle size of 1.7 mm or more and less than 2.8 mm
24 wt% of a particulate water-containing polymer having a particle size of 0.85 mm or more and less than 1.7 mm
59% by weight of a particulate hydropolymer having a particle size of 0.15 mm or more and less than 0.85 mm
11% by weight of a particulate hydropolymer having a particle size of less than 0.15 mm
The solid content concentration of the particulate hydropolymer (18a) was 94% by weight, and the weight average particle size was 0.4 mm. No deposits were found inside the dry meister after operation.
[0207]
The dried and pulverized particulate hydropolymer (18a) had a GV of 40 g / g, a soluble content of 15% by weight, and a residual monomer content of 400 ppm.
[0208]
-Example 19-
After one piece of the water-containing polymer (11) having a large amount of wrinkles obtained in Example 11 was cut into four roughly with a circular saw, a tabletop dual-purpose crusher (FDS type Miyako product, screen diameter 1 mm, Hammer crusher type crusher), but clogged immediately and was not discharged. Therefore, when a dust collector (Machita Corp. wet and dry business model 406) was connected to the discharge port and an air flow was created in the grinder, it was discharged smoothly. The solid content concentration of the discharged product was 78% by weight, and the weight average particle size was 650 μm. Among them, the particle size of 150 μm or less was 7% by weight.
[0209]
It is considered that the aeration during the pulverization quickly took away the water generated by the heat generated during the pulverization, and the adhesiveness of the material was reduced, so that the pulverization became possible.
[0210]
-Example 20-
One hydrated polymer (11) with a lot of wrinkles obtained in Example 11 was roughly cut into four pieces with a circular saw and then cut into a cutter mill (manufactured by Horai Co., Ltd., UG03-280LFT, screen diameter: 8 mm). I put it in. This cutter mill has a blower (DF fan, DF-3, air flow 15m^Three/ Min, manufactured by Horai Co., Ltd.) and a cyclone are connected, and the crushed one is obtained from the lower part of the cyclone. The particulate hydropolymer (20) obtained by pulverization had a solid content concentration of 72% by weight and a weight average particle size of 3 mm. The particle size distribution of this particulate hydropolymer (20) determined with a Ro-Tap sieve shaker was as shown below.
17% by weight of particulate hydropolymer with a particle size of 4 mm or more
69% by weight of a particulate hydropolymer having a particle size of 2 mm or more and less than 4 mm
13% by weight of particulate water-containing polymer having a particle size of 1 mm or more and less than 2 mm
1% by weight of particulate hydropolymer with a particle size of less than 1 mm
Next, this particulate hydropolymer (20) was put into a mesh mill (manufactured by Horai Co., Ltd., HA8-2542, screen diameter 2 mm) and further pulverized. The solid content concentration of the particulate hydropolymer (20a) collected by the cyclone was 75% by weight, and the weight average particle size was 0.6 mm. The throughput was 130 kg per hour. The particle size distribution of this particulate hydropolymer (20a) determined with a Ro-Tap sieve shaker was as shown below.
Particulate water-containing polymer having a particle size of 1.4 mm or more 0% by weight
8% by weight of particulate water-containing polymer having a particle size of 1 mm or more and less than 1.4 mm
17% by weight of particulate water-containing polymer having a particle size of 0.85 mm or more and less than 1 mm
72% by weight of a particulate hydropolymer having a particle size of 0.15 mm or more and less than 0.85 mm
3% by weight of a particulate hydropolymer having a particle size of less than 0.15 mm
No deposits were observed inside the mesh mill after operation.
[0211]
-Example 21-
83.5 parts of acrylic acid, 62.1 parts of 48.5% by weight NaOH aqueous solution, 54.3 parts of ion-exchanged water, 0.11 part of polyethylene glycol diacrylate (number average degree of polymerization of ethylene oxide = 8) as a crosslinking agent , And 0.01 part of 2-hydroxy-2-methyl-1-phenyl-propan-1-one as an initiator to mix a monomer concentration of 50% by weight, a neutralization rate of 65 mol%, and a temperature of 86 ° C. A monomer aqueous solution was prepared (the monomer aqueous solution preparation operation was similarly performed in another batch, and the amount of dissolved oxygen was measured to be 3.0 ppm). This monomer aqueous solution was placed on a 90 ° C. hot plate and poured into a Teflon-coated stainless steel container having a bottom surface of 200 × 260 mm into which nitrogen gas was introduced. When the aqueous monomer solution reaches 80 ° C., it is irradiated with ultraviolet rays for 10 minutes using a black light fluorescent lamp (light quantity: 780 mJ / cm²), And a hydrous polymer (21) having a thickness of about 3 mm was obtained. The solid content concentration was 60% by weight. Therefore, the concentration ratio was 1.20. The maximum temperature during this polymerization was 110 ° C. The water-containing polymer (21) is chopped with a vertical crusher (model VM27-S, screen diameter 3 mm, manufactured by Orient Co., Ltd.), and is in the form of particles having a weight average particle diameter of 1.6 mm and a solid content concentration of 61% by weight. A water-containing polymer (21) was obtained. This particulate water-containing polymer (21) was dried with hot air at 170 ° C. for 30 minutes and pulverized with a desktop pulverizer. Subsequently, the pulverized product was classified with a sieve screen having openings of 600 μm and 300 μm to obtain a base polymer (21) having a particle size of 300 to 600 μm.
[0212]
The base polymer (21) had a GV of 58 g / g, a soluble content of 16 wt%, a neutralization rate of 68 mol%, and a residual monomer content of 2200 ppm.
[0213]
Subsequently, 100 parts of the base polymer (21) was mixed with a surface cross-linking agent composition liquid consisting of 0.05 part of ethylene glycol diglycidyl ether, 1 part of propylene glycol, and 2 parts of water, and the resulting mixture was heated to 80 ° C. A surface-crosslinked water-absorbing resin (21) having a crosslinked surface was obtained by heat treatment in a dryer for 40 minutes.
[0214]
The surface cross-linked water-absorbent resin (21) had a GV of 42 g / g and an AAP of 36 g / g.
Table 4 summarizes the pulverization of the hydropolymers of Examples 11 to 15 and 17 to 21.
[0215]
[Table 4]

[0216]
-Comparative Example 3-
When one sheet of the water-containing polymer (11) having a lot of wrinkles obtained in Example 11 was cut into four roughly with a circular saw, it was put into a meat chopper (manufactured by Hiraga Seisakusho) having a die with a hole diameter of 8 mm. The load was too great to stop immediately and not be crushed.
[0217]
-Comparative Example 4-
A water-containing polymer (11) having a lot of wrinkles obtained in Example 11 was cut into approximately four pieces with a circular saw, and then a sample mill having a screen diameter of 3 mm (KIIW-1 type, Fuji Paudal Co., Ltd.) The load was too large and it immediately stopped and was not crushed.
[0218]
-Comparative Example 5-
When one sheet of the water-containing polymer (11) having a lot of wrinkles obtained in Example 11 was put into a kneader having a sigma type wing (2.5 L internal volume, manufactured by Koike Tekko Co., Ltd.), it was kneaded. It was not broken up.
[0219]
-Comparative Example 6
One hydrated polymer (11) having a lot of wrinkles obtained in Example 11 was cut into approximately four pieces with a circular saw and then put into the apparatus shown in FIG. 4 of JP-A-11-188727. I was stuck and was not crushed.
[0220]
-Comparative Example 7-
9.25 g of polyethylene glycol diacrylate (number average degree of polymerization of ethylene oxide = 8) was dissolved in 5500 g of an aqueous solution of sodium acrylate having a neutralization rate of 65 mol% (monomer concentration: 30% by weight) to prepare a reaction solution. . Next, this reaction solution was degassed for 30 minutes in a nitrogen gas atmosphere. Next, the above reaction solution was supplied to a reactor formed by attaching a lid to a stainless steel double-armed kneader with an internal volume of 10 L having two sigma-shaped blades, and the system was kept at 30 ° C. while maintaining the reaction solution at 30 ° C. The gas was replaced. Subsequently, while stirring the reaction solution, 1.91 g of 2,2′-azobis (2-amidinopropane) dihydrochloride, 0.96 g of sodium persulfate and 0.10 g of L-ascorbic acid were added. Polymerization started after minutes. Then, polymerization was carried out at 30 ° C. to 80 ° C., and the hydrous polymer was taken out 60 minutes after the start of the polymerization. The obtained hydropolymer was subdivided into about 5 mm in diameter. This finely divided water-containing polymer was spread on a 50 mesh wire net and dried with hot air at 150 ° C. for 90 minutes. Subsequently, the dried product was pulverized using a vibration mill, and further classified with a 20-mesh wire mesh to obtain an amorphous crushed comparative base polymer (7) having a weight average particle size of 300 μm. To 100 parts of the obtained comparative base polymer (7), 0.005 part of diethylenetriaminepentaacetic acid pentasodium, 1 part of propylene glycol, 0.05 part of ethylene glycol diglycidyl ether, 3 parts of water, and 1 part of isopropyl alcohol A surface surface crosslinking agent composition liquid consisting of: The mixture was heat-treated at 210 ° C. for 45 minutes to obtain a comparative surface crosslinked water-absorbing resin (7).
[0221]
-Comparative Example 8-
A 37% by weight aqueous sodium acrylate solution (67.0 parts), acrylic acid 10.2 parts, polyethylene glycol diacrylate (number average degree of polymerization of ethylene oxide = 8) 0.155 parts, and water 22.0 parts were mixed. A meter aqueous solution was prepared. Nitrogen was blown into the aqueous solution in a vat so that the dissolved oxygen in the monomer aqueous solution was 0.1 ppm or less. Subsequently, the temperature of the aqueous solution was adjusted to 18 ° C. under a nitrogen atmosphere, and then 0.16 part of a 5 wt% sodium persulfate aqueous solution, 5 wt% 2, 2′-azobis (2-amidinopropane) dihydrochloride aqueous solution 0 .16 parts, 0.55% by weight L-ascorbic acid aqueous solution 0.15 parts, and 0.35% by weight hydrogen peroxide aqueous solution 0.17 parts were added dropwise with stirring in this order. Polymerization started immediately after the dropwise addition of hydrogen peroxide, and the temperature of the monomer aqueous solution reached a peak temperature of 85 ° C. 10 minutes later. Subsequently, the vat was immersed in an 80 ° C. water bath and aged for 15 minutes. The obtained transparent water-containing polymer was crushed with a meat chopper, and the finely divided water-containing polymer was spread on a 50-mesh wire net and dried with hot air at 160 ° C. for 65 minutes. Subsequently, the dried product was pulverized by a pulverizer, and further classified into what passed through an 850 μm sieve and remained on the 106 μm sieve, to obtain an amorphous crushed comparative base polymer (8) having a weight average particle diameter of 320 μm. A surface surface cross-linking agent composition liquid consisting of 1 part of propylene glycol, 0.5 part of 1,4-butanediol, 3 parts of water and 1 part of isopropyl alcohol is added to 100 parts of the obtained comparative base polymer (8). Mixed. The mixture was heat-treated at 210 ° C. for 40 minutes to obtain a comparative surface crosslinked water-absorbing resin (8).
[0222]
Further, the surface crosslinked water-absorbing resins (2), (3), (5), and (6) of Examples 2, 3, 5, and 6, and the comparative surface crosslinked water-absorbing resins (1) of Comparative Examples 1, 7, and 8, respectively. , (7), (8), Comparative Base Polymers (1), (7), (8) of Comparative Examples 1, 7, 8 and GV, AAP, Solubilization Residual Ratio, GV X Table 5 shows the results of comparison of solubilization residual ratio.
[0223]
[Table 5]

[0224]
【The invention's effect】
By a rational process, it is possible to provide a base polymer having a high absorption capacity under no load and a small amount of soluble component, and a water absorbent resin having a high absorption capacity under pressure subjected to surface crosslinking.
[0225]
Because of the above effects, the water-absorbent resin obtained by the present invention is used in contact with human bodies such as sanitary products (diapers for children and adults, sanitary napkins, incontinent products for adults, etc.); It is useful as a water-stopping material for electric wire or optical cable;
[Brief description of the drawings]
1 is a graph showing the relationship between polymerization reaction temperature and time in Examples 3 and 7 to 10. FIG. Time zero is when light irradiation is started.
2 is a side view photograph of the water-containing polymer obtained in Example 1. FIG.
3 is a side view photograph of the water-containing polymer obtained in Example 3. FIG.
4 is a top view photograph of the water-containing polymer obtained in Example 3. FIG.
5 is a photograph of the bottom surface of the water-containing polymer obtained in Example 3. FIG.
6 is a side view photograph of the water-containing polymer obtained in Example 5. FIG.
7 is a side view photograph of the water-containing polymer obtained in Example 7. FIG.
FIG. 8 is a photograph of a gel obtained by cutting out a part of the hydropolymer of Example 7 and swelling it with tap water.

Claims (6)

In a method for producing a water absorbent resin by polymerizing a monomer component mainly composed of acrylic acid and / or a sodium salt thereof in an aqueous solution,
(1) The concentration of the monomer component in the aqueous solution is 45% by weight or more,
(2) polymerizing while evaporating moisture so that the ratio (concentration ratio) of the solid content concentration of the hydrous polymer produced by polymerization and the solid content concentration in the monomer aqueous solution is 1.10 or more;
(3) The solid content concentration of the hydropolymer produced by polymerization is 80% by weight or less,
(4) Subdividing the hydrous polymer produced by polymerization, followed by drying and grinding,
A method for producing a water-absorbent resin, characterized by:   The method for producing a water-absorbent resin according to claim 1, wherein the polymerization is started after the temperature of the aqueous solution is raised using heat of neutralization and / or dissolution of acrylic acid and alkali.   The method for producing a water-absorbent resin according to claim 1 or 2, wherein an increase in the neutralization rate during the polymerization is 2 points or more.   The method for producing a water absorbent resin according to any one of claims 1 to 3, wherein the neutralization rate of acrylic acid is 50 mol% or more and less than 80 mol%.   The method for producing a water-absorbent resin according to any one of claims 1 to 4, wherein the polymerization is carried out under atmospheric pressure.   The method for producing a water-absorbent resin according to any one of claims 1 to 5, wherein an expansion ratio during polymerization is 2 times or more.

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