JP4030403B2 - Method for dispersing dry silica - Google Patents

Description

【００１６】
【発明の実施の形態】
本発明において用いられる乾式シリカは、四塩化珪素を原料として酸水素炎中で燃焼させて得られる、「ヒュームドシリカ」とも称されており、特に制限なく使用される。一般に乾式シリカは、比表面積が３０〜５００ｍ^２／ｇのものが市販されており、これらの乾式シリカは、本発明において好適に使用される。
【００１７】
本発明において、対象とする乾式シリカスラリー中のシリカ濃度は、１０〜３５重量％である。即ち、シリカ濃度が３５重量％より高い場合、乾式シリカが極性溶媒中に取り込まれるときの乾式シリカの凝集力が極端に強くなるため、スラリーの流動性が極端に悪くなり、高速回転剪断型分散機を使用した分散が困難となる。また、１０重量％より少ない場合、乾式シリカの分散効率が低く、長時間の分散が必要となり好ましくない。
【００１８】
本発明において用いられる極性溶媒は、乾式シリカが分散し易い極性溶媒であれば特に制限はない。かかる極性溶媒としては、水やメタノール、エタノール、イソプロピルアルコール等のアルコール類、エーテル類、ケトン類などの極性溶媒が使用でき、また、水と上記極性溶媒との混合溶媒も使用できる。さらに、上記の極性溶媒に予め界面活性剤、カチオン性樹脂等の添加剤を配合してもよい。
【００１９】
本発明において、高速回転剪断型分散機は、図１に代表的な構造を示すように、分散槽３内で、ステーターと呼ばれる固定環１の内壁に沿い、１ｍｍ以内のクリアランスを保った状態でタービン（回転翼）２を高速回転させ、処理液を分散する分散機である。
【００２０】
該高速回転剪断型分散機を用いて乾式シリカをスラリー化する際、タービン・ステーター間に発生する剪断力、及びキャビテーションによる衝撃力により、極性溶媒中において凝集する乾式シリカを分散し、極性溶媒中での凝集現象を抑制する。
【００２１】
本発明に用いられる高速回転剪断型分散機は、上述した機能を有するものであれば特に限定されない。具体例を挙げると、ウルトラミキサー（みづほ工業製）、ホモジナイザー（ＩＫＡ製）、ホモミキサー、ホモジェッター（特殊機化工業製）、クリアミックス（エムテクニックス製）、更には該高速回転剪断型分散機にディスパー型の高速回転遠心放射型攪拌機やプロペラ型の一般攪拌機、あるいはアンカー型、プラネタリー型の混練分散機を組み合わせて使用するコンビミックスタイプなどがあるが、好ましくは、極性溶媒の界面中央部にボルテックスを形成させ、添加した乾式シリカがボルテックスによってタービンへと直接的に取り込まれるような流動状態を発生させる分散機、ウルトラミキサー、ホモジェッターを用いるのが好ましい。
【００２２】
また、該高速回転剪断型分散機は、前記図１に示すように、タービン径（ｄ）と分散槽内径（Ｄ）との比（ｄ／Ｄ）が０．０５〜０．５、好ましくは、０．１〜０．４の範囲にあるものが使用される。即ち、ｄ／Ｄが０．０５より小さい場合、タービン径に対する分散槽内径が大きすぎるため、特に、分散槽内壁付近における流速が遅くなり、スラリーの分散状態が悪くなる。また、ｄ／Ｄが０．５より大きい場合、タービン径に対する分散槽内径が小さすぎ、スラリーにかかる剪断力が大きくなりすぎるため、スラリーの流動状態が大きく乱れ、分散機への負荷が増大する。
【００２３】
また、本発明に使用する高速回転剪断型分散機は、上記分散槽内径が、５０〜１５００ｍｍ、特に１００〜１２００ｍｍのものが一般的である。
【００２４】
本発明において、極性溶媒は予め高速回転剪断型分散機中に供給され、これに乾式シリカを特定の供給速度で供給して分散が行われる。かかる乾式シリカを極性溶媒中に添加する方法としては、特に限定されず、高速回転剪断型分散機中の極性溶媒の液面に乾式シリカを直接添加する方法、高速回転剪断型分散機のタービン近くに乾式シリカの添加口を設置し、渦の中心部に乾式シリカを添加する方法などが好適に採用される。
【００２５】
本発明においては、高速回転剪断型分散機のタービンの周速（ｕ；ｍ／秒）、吐出量（Ｑ；ｋｇ／秒）、及び極性溶媒の重量（Ｗ；ｋｇ）が式（１）の範囲となる条件において乾式シリカを添加し分散を行うことが重要である。
【００２６】
５≦（Ｑ×ｕ^２／Ｗ）≦２００ （１）
上記式において、（Ｑ×ｕ^２／Ｗ）の単位は（Ｊ／ｋｇ／秒）となるので、（Ｑ×ｕ^２／Ｗ）は極性溶媒が単位質量、単位時間当たりにタービンに通過するときに与えられる分散エネルギーと考えられる。
【００２７】
本発明にあっては、タービンの周速、吐出量、及び極性溶媒の重量によって特定される極性溶媒の単位重量あたりの分散エネルギーを上記一定の範囲内に調整することが重要であり、後記する乾式シリカの添加速度の調整との組み合わせによって、乾式シリカが高濃度で、高分散した乾式シリカスラリーを得ることができる。
【００２８】
即ち、前記（Ｑ×ｕ^２／Ｗ）が式（１）で示される範囲より小さい場合は、スラリーに与える分散エネルギーが不足するため、乾式シリカの分散状態が悪くなり、スラリーのゲル化を引き起こすため好ましくない。また（Ｑ×ｕ^２／Ｗ）が式（１）で示される範囲より大きい場合は、極性溶媒にかかる剪断力が大きすぎるため、乾式シリカのスラリー化において、スラリーの流動状態の悪化、分散機への負荷増大が起こる。更には、極性溶媒中の取り込まれた乾式シリカの凝集が顕著となり、スラリーがゲル化する。この現象は、乾式シリカを添加した場合、乾式シリカが極性溶媒中に取り込まれる速度は速いが、表面が十分ぬれていない状態で乾式シリカが多量に極性溶媒中に取り込まれるためではないかと推定される。
【００２９】
前記タービンの吐出量とは、分散槽内の処理液がタービンに吸引された後、タービン・ステーター間から吐出される量を示している。一般的に吐出量（Ｑ；ｍ^３／分）は、タービンの回転数（ｎ；１／分）、タービン径（ｄ；ｍ）、及び吐出係数（Ｋ；−）により（３）式で求められる。
【００３０】
Ｑ＝Ｋ×ｎ×ｄ^３ （３）
高速回転剪断型分散機を用いる場合、吐出量は０．００５〜２ｍ^３／分、特に、０．０１〜１．５ｍ^３／分の範囲で用いることが好ましい。かかる吐出量の調整は、タービンの大きさ、羽根の角度などの形状、タービン・ステーター間のクリアランスなどにより調整することができる。また、タービンの周速は、式（１）の範囲内で、タービンの吐出量、及び極性溶媒の重量を勘案して調整することが好ましい。
【００３１】
一般に、乾式シリカは嵩密度が低く、極性溶媒界面において堆積、凝集し易いため、本発明においては、乾式シリカが極性溶媒界面上に堆積しないように添加速度を調整することが必要である。具体的には、高速回転剪断型分散機の運転条件を勘案して乾式シリカの添加速度を決定することが必要である。即ち、乾式シリカの添加速度（ｖ；ｋｇ／秒）、及び極性溶媒の重量（Ｗ；ｋｇ）との比によって表される、極性溶媒の単位重量あたりの乾式シリカの添加速度が、前記式（２）で示される範囲に調整することが重要である。
【００３２】
Ａ≦（ｖ／Ｗ）≦Ｂ （２）
【００３３】
【数３】

【００３４】
式（２）は、乾式シリカの添加速度を、極性溶媒にかかる分散エネルギーとの関係で一定の範囲内に保った状態で調整することを示している。即ち、（ｖ／Ｗ）が式（２）で示される範囲より小さいときは、乾式シリカの添加速度が遅く、乾式シリカをスラリー化するのに要する時間がかかるため、工業的生産には適さない。また式（２）で示される範囲より大きいときは、逆に添加速度が速くなりすぎて分散しきれず、スラリーがゲル化するため、好ましくない。即ち、本発明において、乾式シリカのスラリー化において、高濃度で、高分散に、且つ効率よくスラリー化するためには、式（２）の範囲を満足することが重要である。
【００３５】
本発明において、前述した式（１）及び（２）に示した分散条件を同時に満足することが極めて重要であり、どちらかひとつの条件を欠いても、高濃度で、高分散に、且つ効率よくスラリー化することができない。
【００３６】
乾式シリカ分散液の粘度は、インクジェット記録材料やＯＨＰ用コート剤の塗工液として使用する際に、低粘度であることが好ましい。従って、本発明の方法を採用することによって、乾式シリカをスラリー化する途中、及びスラリー化後に得られる乾式シリカスラリーの粘度は、１０００ｍＰａ・ｓ、特に５００ｍＰａ・ｓ以下に維持することが可能であり、これによって、塗工液に使用するに適した乾式シリカ分散液の製造が可能となる。
【００３７】
また、本発明において、乾式シリカをスラリー化する場合、乾式シリカが高濃度になるほど、分散による発熱が多くなるため、乾式シリカのスラリー化を行うときの温度を、１５℃以上４０℃以下の範囲に保ちながら行うことが好ましい。温度を保つ方法としては、分散槽に加熱用または冷却用ジャケットを設置し、温度を一定に保つ方法が挙げられる。
【００３８】
【発明の効果】
以上の説明で理解されるように、本発明の乾式スラリーの分散方法は、高濃度で、高分散に、且つ効率よく乾式シリカを極性溶媒に分散させてスラリー化を行うことが可能であり、工業的に極めて有用な方法である。
【００３９】
そして、得られた乾式シリカスラリーは、必要に応じて、更なる分散機により処理して乾式シリカ分散液とし、例えば、インクジェット記録用シートの塗工液の原料などとして好適に使用できる。
【００４０】
【実施例】
以下、本発明の実施例を挙げて具体的に説明するが、本発明はこれらの実施例によって何ら制限されるものではない。
【００４１】
尚、乾式シリカの分散状態を評価するために、下記の方法により行った。
【００４２】
（乾式シリカの分散状態の評価）
処理液の可視光吸収スペクトルを、分光光度計（日本分光製）を用いて測定した。まず、光路長１０ｍｍのセルを用い、参照セル及び試料セルにそれぞれイオン交換水で満たし、全波長範囲にわたってゼロ点校正を行った。次に処理液の濃度を１．５重量％になるようにイオン交換水で希釈し、試料セルに該希釈液を入れて、測定波長（λ）４６０〜７００ｎｍの範囲の吸光度（τ）を測定した。ｌｏｇ（λ）とｌｏｇ（τ）をプロットし、下記に示す式（４）を用いて直線の傾き（−ｎ）を最小二乗法により求めた。
【００４３】
τ＝αλ^−ｎ （４）
こうして求めたｎは光散乱指数と呼ばれ、本発明における乾式シリカの分散状態を示す指標として採用した。ｎが高いほど乾式シリカの分散状態が良いことを示す。
【００４４】
（粘度の測定）
乾式シリカスラリー３００ｇを５００ｃｃ容器に採取し、Ｂ型粘度計（トキメック製、ＢＬ）を用いて６０ｒｐｍの条件においてスラリーの粘度を測定した。
【００４５】
実施例１
乾式シリカの分散条件において、周速ｕを９．４（ｍ／秒）、吐出量Ｑを０．６１（ｋｇ／秒）に設定した。予め分散槽にイオン交換水を１６００ｇ仕込んだ後、比表面積３００ｍ^２／ｇの乾式シリカ粉（レオロシールＱＳ３０、トクヤマ製）５００ｇを分散槽に添加しながら、ウルトラミキサー（みづほ工業製）によりスラリー化を行った。このときの添加速度ｖ／Ｗを２．１×１０^−４（１／秒）、ｄ／Ｄを０．３０とした。分散条件を表１に、このときの得られた乾式シリカスラリーの物性を表２に示す。このときの分散エネルギー（Ｑ×ｕ^２／Ｗ）は３３．７（Ｊ／ｋｇ／秒）であり、分散エネルギー及び添加速度は、式（１）、（２）の範囲内であった。得られた乾式シリカスラリーのｎ値は２．７であり、乾式シリカの分散状態は良好であった。
【００４６】
比較例１
周速ｕを４．７（ｍ／秒）、吐出量Ｑを０．３０（ｋｇ／秒）、添加速度ｖ／Ｗを５．６×１０^−５（１／秒）、及び乾式シリカの添加量３００ｇに変更した以外は実施例１と同様のスラリー化を行った。分散条件を表１に、このときの得られた乾式シリカスラリーの物性を表２に示す。このときの分散エネルギー（Ｑ×ｕ^２／Ｗ）は４．２（Ｊ／ｋｇ／秒）であり、分散エネルギーが式（１）の範囲より小さかったため、得られた乾式シリカスラリーのｎ値は１．７であり、乾式シリカの分散状態が悪かった。
【００４７】
比較例２
周速ｕを１８．８（ｍ／秒）、吐出量Ｑを１．２２（ｋｇ／秒）、添加速度ｖ／Ｗを４．７×１０^−４（１／秒）に変更した以外は、実施例１と同様のスラリー化を行った。乾式シリカ添加開始後、乾式シリカ粉は迅速にイオン交換水中に取り込まれていたが、乾式シリカ粉の添加量が４８０ｇになった時点で流動性が急激に悪くなり、スラリー全体がゲル化したため、目標とした５００ｇ全量を添加できなかった。このときの分散エネルギー（Ｑ×ｕ^２／Ｗ）は２６９．５（Ｊ／ｋｇ／秒）であり、分散エネルギーが式（１）の範囲よりも大きかった。
【００４８】
実施例２
乾式シリカの分散条件において、周速ｕを１８．３（ｍ／秒）、吐出量Ｑを７．００（ｋｇ／秒）に設定した。予め分散槽にイオン交換水を２００ｋｇ仕込んだ後、比表面積３００ｍ^２／ｇの乾式シリカ（レオロシールＱＳ３０、トクヤマ製）５０ｋｇを分散槽に添加しながら、ウルトラミキサー（みづほ工業製）によりスラリー化を行った。このときの添加速度ｖ／Ｗを１．１×１０^−４（１／秒）、ｄ／Ｄを０．１３とした。分散条件を表１に、このときの得られた乾式シリカスラリーの物性を表２に示す。このときの分散エネルギー（Ｑ×ｕ^２／Ｗ）は１１．７（Ｊ／ｋｇ／秒）であり、分散エネルギー及び添加速度は、式（１）、（２）の範囲内であった。得られた乾式シリカスラリーのｎ値は２．８であり、乾式シリカの分散状態が良好であった。
【００４９】
比較例３
添加速度ｖ／Ｗを４．２×１０^−４（１／秒）に変更した以外は、実施例２と同様のスラリー化を行った。乾式シリカ粉は迅速にイオン交換水中に取り込まれていたが、乾式シリカ粉の添加量が４０ｋｇになった時点で流動性が急激に悪くなり、スラリー全体がゲル化したため、目標とした５０ｋｇ全量を添加できなかった。このときの分散エネルギー（Ｑ×ｕ^２／Ｗ）は１１．７であり、乾式シリカの添加速度が式（２）の範囲よりも大きかった。
【００５０】
実施例３
乾式シリカの分散条件において、周速ｕを１０．６（ｍ／秒）、吐出量Ｑを０．６８（ｋｇ／秒）に設定した。予め分散槽にイオン交換水を２４００ｇ仕込んだ後、比表面積９０ｍ^２／ｇの乾式シリカ粉（レオロシールＱＳ０９、トクヤマ製）６００ｇを分散槽に添加しながら、ウルトラミキサー（みづほ工業製）によりスラリー化を行った。このときの添加速度ｖ／Ｗを２．３×１０^−４（１／秒）、ｄ／Ｄ＝０．２４とした。分散条件を表１に、このときの得られた乾式シリカスラリーの物性を表２に示す。このときの分散エネルギー（Ｑ×ｕ^２／Ｗ）は３２．０（Ｊ／ｋｇ／秒）であり、分散エネルギー及び添加速度は、式（１）、（２）の範囲内であった。得られた乾式シリカスラリーのｎ値は３．０であり、乾式シリカの分散状態が良好であった。
【００５１】
実施例４
乾式シリカの分散条件において、周速ｕを１１．０（ｍ／秒）、吐出量Ｑを０．６３（ｋｇ／秒）に設定した。予め分散槽にイオン交換水を１６００ｇ仕込んだ後、比表面積３００ｍ^２／ｇの乾式シリカ粉（レオロシールＱＳ３０、トクヤマ製）４００ｇを分散槽に添加しながら、ホモジナイザー（ＩＫＡ製）によりスラリー化を行った。このときの添加速度ｖ／Ｗを１．７×１０^−４（１／秒）、ｄ／Ｄを０．２０とした。分散条件を表１に、このときの得られた乾式シリカスラリーの物性を表２に示す。このときの分散エネルギー（Ｑ×ｕ^２／Ｗ）は３２．０（Ｊ／ｋｇ／秒）であり、分散エネルギー及び添加速度は式（１）、（２）の範囲内であった。得られた乾式シリカスラリーのｎ値は２．５であり、乾式シリカの分散状態が良好であった。
【００５２】
実施例５
乾式シリカの分散条件において、周速ｕを１５．７（ｍ／秒）、吐出量Ｑを３．３８（ｋｇ／秒）に設定した。予め分散槽にイオン交換水を４０ｋｇ仕込んだ後、比表面積３００ｍ^２／ｇの乾式シリカ（レオロシールＱＳ３０、トクヤマ製）１０ｋｇを分散槽に添加しながら、ウルトラミキサー１基、プロペラミキサー１基、及びアンカー１基を設置したコンビミックスタイプの分散機（みづほ工業製）によりスラリー化を行った。このときの添加速度ｖ／Ｗを１．２×１０^−４（１／秒）、ｄ／Ｄ＝０．１２に設定し、分散条件を表１に、このときの得られた乾式シリカスラリーの物性を表２に示す。このときの分散エネルギー（Ｑ×ｕ^２／Ｗ）は２０．８（Ｊ／ｋｇ／秒）であり、分散エネルギー及び添加速度は式（１）、（２）の範囲内であった。得られた乾式シリカスラリーのｎ値は２．６であり、乾式シリカの分散状態が良好であった。
【００５３】
比較例４
乾式シリカの分散条件において、周速ｕを１６．５（ｍ／秒）、吐出量Ｑを１．０６（ｋｇ／秒）に設定した。予め分散槽にイオン交換水を１２８０ｇ仕込んだ後、比表面積３００ｍ^２／ｇの乾式シリカ（レオロシールＱＳ３０、トクヤマ製）３４０ｇを分散槽に添加しながら、ウルトラミキサー（みづほ工業製）によりスラリー化を行った。このときの添加速度ｖ／Ｗを４．２×１０^−４（１／秒）、ｄ／Ｄ＝０．３２とした。分散条件を表１に、このときの得られた乾式シリカスラリーの物性を表２に示す。このときの分散エネルギー（Ｑ×ｕ^２／Ｗ）は２２５．７（Ｊ／ｋｇ／秒）であり、分散エネルギーが式（１）の範囲よりも大きかったため、乾式シリカスラリーのｎ値は２．１であり、乾式シリカの分散状態が悪く、乾式シリカスラリーは高粘度であった。
【００５４】
【表１】

【００５５】
【表２】

【００５６】
表１、表２に見られるように、タービンの周速、吐出量、乾式シリカの添加速度、及び極性溶媒の重量を式（１）、（２）を同時に満足する範囲に調整することにより、乾式シリカの分散状態が良く、低粘度な乾式シリカスラリーが得られた。
【００５７】
また、式（１）、（２）で示した範囲内で乾式シリカのスラリー化を行った実施例１〜５によって得られた乾式シリカスラリーは、式（１）の範囲外で乾式シリカのスラリー化を行った比較例１、４によって得られた乾式シリカスラリーと比較してn値が高く、分散状態が良好であり、かつ低粘度であった。また、式（１）で示した範囲外で乾式シリカのスラリー化を行った比較例２、式（２）の範囲外で乾式シリカのスラリー化を行った比較例３に関しては、目標とする乾式シリカの濃度に達する前にスラリー全体がゲル化した。
【図面の簡単な説明】
【図１】本発明に使用する高速回転剪断型分散機の代表的な構造を示す概略図
【符号の説明】
１ ステーター
２ タービン
３ 分散槽[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel dispersion method for dispersing dry silica in a polar solvent using a high-speed rotary shear type disperser. More specifically, the present invention relates to a method for dispersing dry silica that can achieve high concentration and high dispersion when dry silica is added to a polar solvent and dispersed using a high-speed rotary shear disperser.
[0002]
[Prior art]
Dry silica produced by burning silicon tetrachloride in an oxyhydrogen flame as a raw material is suitably used as a raw material for inkjet recording materials and OHP coating agents because of its high transparency.
[0003]
The dry silica is often used for each raw material as a so-called dry silica dispersion in which dry silica is dispersed and stabilized in a polar solvent.
[0004]
As a method for producing such a dry silica dispersion, many known techniques have been reported so far.
[0005]
For example, as shown in Patent Document 1, after adding dry silica fine particles in a polar solvent and dispersing to form a dry silica slurry, this is mixed with an additive such as a cationic resin, and further, a high pressure homogenizer or super There has been proposed a method of obtaining a dry silica dispersion by performing fine dispersion treatment with a sonic disperser or the like. Furthermore, as shown in Patent Document 2 and Patent Document 3, after adding dry silica in a polar solvent containing a dispersion aid such as a cationic resin to disperse it into a dry silica slurry, a high-pressure homogenizer or ultrasonic wave is added. There has been proposed a method of obtaining a dry silica dispersion by performing fine dispersion treatment with a disperser or the like.
[0006]
Hereinafter, the process of adding and dispersing dry silica in a polar solvent is the process of slurrying dry silica, the process obtained by the process of slurrying dry silica is finely dispersed with a dry silica slurry, and further with a high-pressure homogenizer, ultrasonic disperser, etc. What is obtained after carrying out is expressed as a dry silica dispersion.
[0007]
Dispersing devices used to disperse dry silica in a polar solvent in a dry silica slurrying process include general stirrers, high-speed rotary shear type dispersers, high-speed rotary centrifugal radiation type stirrers, kneading dispersers, and pulverizing dispersers A known dispersion machine such as, or a batch-type dispersion apparatus equipped with a dispersion tank of a combination type that combines these, and dry silica and a polar solvent are quantitatively sent to the dispersion part by a pump action, Examples thereof include a continuous dispersion apparatus that performs dispersion.
[0008]
When manufacturing a dry silica dispersion, it is possible to increase the concentration of the dispersion and reduce the processing time from the manufacturing cost of the dispersion, the distribution cost, and the reduction of the drying cost in the coating process of the coating liquid containing the dispersion. Efficiency is very important. In addition, in order to produce a dry silica dispersion, a dry silica slurrying step is essential. In order to increase the concentration of the dry silica dispersion and shorten the processing time, first, in this slurrying step, It is essential to obtain a high concentration and highly dispersed dry silica slurry.
[0009]
When slurrying dry silica using the high-speed rotary shearing disperser shown above, the cohesive force between the silica particles increases as the dry silica concentration in the polar solvent increases, so the aggregated silica particles are dispersed. While dry silica must be added. Conventionally, as exemplified in Patent Document 4, by using a high-speed rotary shearing disperser and increasing the peripheral speed of the turbine to increase the dispersion force, high-concentration, high-dispersion dry silica is used. Attempts have been made to slurry.
[0010]
However, in the slurrying process of dry silica using the high-speed rotary shear type disperser, simply increasing the peripheral speed of the turbine causes deterioration of the flow state of the slurry and increase of the load on the disperser, and the resulting dry type The dispersion state of the silica slurry is poor, and in the worst case, there is a problem that the slurry is gelled, and development of a dispersion method for efficiently obtaining a high concentration dry silica slurry has not yet been successful.
[0011]
[Patent Document 1]
JP 11-321079 A [Patent Document 2]
JP 2001-19421 A [Patent Document 3]
JP 2002-178626 A [Patent Document 4]
JP 2002-178626 A [Problems to be Solved by the Invention]
Accordingly, an object of the present invention is to efficiently and industrially produce a high-concentration, high-dispersion dry silica slurry in the process of slurrying dry silica using a high-speed rotary shear disperser. Is to provide.
[0012]
[Means for Solving the Problems]
As a result of intensive studies on the above problems, the inventors of the present invention have no effect in simply increasing the peripheral speed of the turbine when slurrying dry silica using a high-speed rotary shear disperser, In addition to the peripheral speed, by adjusting the discharge rate of the turbine, the addition rate of the dry silica, and the weight of the polar solvent to have a specific relationship, it is possible to efficiently produce a high concentration, highly dispersed dry silica slurry for the first time. The present invention has been completed by finding out what can be done.
[0013]
That is, the present invention uses a high-speed rotary shearing disperser in which the ratio (d / D) of the turbine diameter (d) to the dispersion tank inner diameter (D) is 0.05 to 0.5, and polarizes dry silica. A method of adding and dispersing in a solvent, the peripheral speed (u; m / sec) of the turbine of the high-speed rotary shearing disperser, the discharge rate of the turbine (Q; kg / sec), the addition rate of dry silica (V: kg / sec) and the dry silica is dispersed under the condition that the weight of the polar solvent (W; kg) is within the range satisfying the formulas (1) and (2) at the same time. This is a dispersion method.
[0014]
5 ≦ (Q × u ² / W) ≦ 200 (1)
A ≦ (v / W) ≦ B (2)
[0015]
[Expression 2]

[0016]
DETAILED DESCRIPTION OF THE INVENTION
The dry silica used in the present invention is also referred to as “fumed silica” obtained by burning silicon tetrachloride as a raw material in an oxyhydrogen flame, and is used without particular limitation. In general, dry silica having a specific surface area of 30 to 500 m ² / g is commercially available, and these dry silicas are suitably used in the present invention.
[0017]
In the present invention, the silica concentration in the target dry silica slurry is 10 to 35% by weight. That is, when the silica concentration is higher than 35% by weight, the cohesive force of the dry silica becomes extremely strong when the dry silica is taken into the polar solvent, so that the fluidity of the slurry becomes extremely poor, and the high-speed rotational shear dispersion Dispersion using a machine becomes difficult. On the other hand, when it is less than 10% by weight, the dispersion efficiency of dry silica is low, and dispersion for a long time is required, which is not preferable.
[0018]
The polar solvent used in the present invention is not particularly limited as long as it is a polar solvent in which dry silica is easily dispersed. As such a polar solvent, water, alcohols such as methanol, ethanol and isopropyl alcohol, polar solvents such as ethers and ketones can be used, and a mixed solvent of water and the above polar solvent can also be used. Furthermore, you may mix | blend additives, such as surfactant and a cationic resin, with said polar solvent previously.
[0019]
In the present invention, as shown in FIG. 1, the high-speed rotary shear type disperser has a clearance of 1 mm or less along the inner wall of the stationary ring 1 called a stator in the dispersion tank 3 as shown in FIG. This is a disperser that rotates the turbine (rotary blade) 2 at high speed to disperse the processing liquid.
[0020]
When slurrying dry silica using the high-speed rotary shear disperser, the dry silica that aggregates in the polar solvent is dispersed in the polar solvent by the shearing force generated between the turbine and the stator and the impact force caused by cavitation. Suppresses the agglomeration phenomenon.
[0021]
The high-speed rotary shearing disperser used in the present invention is not particularly limited as long as it has the above-described function. Specific examples include an ultra mixer (manufactured by Mizuho Kogyo Co., Ltd.), a homogenizer (manufactured by IKA), a homomixer, a homo jetter (manufactured by Tokushu Kika Kogyo Co., Ltd.), a clear mix (manufactured by M Techniques), and the high-speed rotational shear type dispersion. There are disperse type high-speed rotary centrifugal radiation type agitator, propeller type general agitator, or combination type using a combination of anchor type and planetary type kneading disperser, but preferably at the interface center of polar solvent It is preferable to use a disperser, an ultramixer, or a homojetter that forms a vortex in the part and generates a fluid state in which the added dry silica is directly taken into the turbine by vortexing.
[0022]
Further, as shown in FIG. 1, the high-speed rotary shear type disperser has a ratio (d / D) of the turbine diameter (d) to the dispersion tank inner diameter (D) of 0.05 to 0.5, preferably And those in the range of 0.1 to 0.4 are used. That is, when d / D is smaller than 0.05, the inner diameter of the dispersion tank relative to the turbine diameter is too large, so that the flow velocity in the vicinity of the inner wall of the dispersion tank is particularly slow and the dispersion state of the slurry is deteriorated. When d / D is larger than 0.5, the inner diameter of the dispersion tank relative to the turbine diameter is too small and the shearing force applied to the slurry becomes too large, so that the flow state of the slurry is greatly disturbed and the load on the disperser increases. .
[0023]
The high-speed rotary shear type disperser used in the present invention generally has a dispersion tank inner diameter of 50 to 1500 mm, particularly 100 to 1200 mm.
[0024]
In the present invention, the polar solvent is supplied in advance into a high-speed rotary shearing type disperser, and dry silica is supplied thereto at a specific supply rate for dispersion. The method of adding such dry silica to the polar solvent is not particularly limited, and is a method of adding dry silica directly to the surface of the polar solvent in the high-speed rotary shear disperser, near the turbine of the high-speed rotary shear disperser. For example, a method of adding a dry silica addition port and adding dry silica to the center of the vortex is suitably employed.
[0025]
In the present invention, the peripheral speed (u; m / sec), the discharge rate (Q; kg / sec), and the weight (W; kg) of the polar solvent of the turbine of the high-speed rotary shear disperser are expressed by the formula (1). It is important to carry out dispersion by adding dry silica under the range of conditions.
[0026]
5 ≦ (Q × u ² / W) ≦ 200 (1)
In the above formula, since the unit of (Q × u ² / W) is (J / kg / second), (Q × u ² / W) is when the polar solvent passes through the turbine per unit mass and unit time. Is considered to be the dispersion energy given to
[0027]
In the present invention, it is important to adjust the dispersion energy per unit weight of the polar solvent specified by the peripheral speed of the turbine, the discharge amount, and the weight of the polar solvent within the above-mentioned predetermined range, which will be described later. By combination with the adjustment of the addition rate of dry silica, a dry silica slurry in which dry silica is highly dispersed and highly dispersed can be obtained.
[0028]
That is, when (Q × u ² / W) is smaller than the range represented by the formula (1), the dispersion energy given to the slurry is insufficient, so that the dispersion state of the dry silica is deteriorated and the gelation of the slurry is caused. Therefore, it is not preferable. In addition, when (Q × u ² / W) is larger than the range represented by the formula (1), the shearing force applied to the polar solvent is too large. An increase in load occurs. Furthermore, the aggregation of the dry silica incorporated in the polar solvent becomes remarkable, and the slurry is gelled. This phenomenon is presumed that when dry silica is added, the speed at which dry silica is taken into the polar solvent is fast, but a large amount of dry silica is taken into the polar solvent when the surface is not sufficiently wet. The
[0029]
The discharge amount of the turbine indicates the amount discharged from between the turbine and the stator after the processing liquid in the dispersion tank is sucked into the turbine. In general, the discharge amount (Q; m ³ / min) is obtained by the equation (3) from the turbine speed (n; 1 / min), the turbine diameter (d; m), and the discharge coefficient (K;-). It is done.
[0030]
Q = K × n × d ³ (3)
When a high-speed rotary shearing type disperser is used, the discharge rate is preferably 0.005 to ² m ³ / min, particularly 0.01 to 1.5 m ³ / min. The discharge amount can be adjusted by adjusting the turbine size, the blade angle, the clearance between the turbine and the stator, and the like. Further, the peripheral speed of the turbine is preferably adjusted in consideration of the discharge amount of the turbine and the weight of the polar solvent within the range of the formula (1).
[0031]
In general, dry silica has a low bulk density and easily deposits and aggregates at the polar solvent interface. Therefore, in the present invention, it is necessary to adjust the addition rate so that dry silica does not deposit on the polar solvent interface. Specifically, it is necessary to determine the addition rate of dry silica in consideration of the operating conditions of the high-speed rotary shearing disperser. That is, the addition rate of dry silica per unit weight of the polar solvent, expressed by the ratio of the addition rate of dry silica (v; kg / second) and the weight of the polar solvent (W; kg) It is important to adjust to the range shown in 2).
[0032]
A ≦ (v / W) ≦ B (2)
[0033]
[Equation 3]

[0034]
Formula (2) indicates that the addition rate of dry silica is adjusted in a state where it is kept within a certain range in relation to the dispersion energy applied to the polar solvent. That is, when (v / W) is smaller than the range represented by formula (2), the addition rate of dry silica is slow and it takes time to slurry dry silica, which is not suitable for industrial production. . On the other hand, when it is larger than the range represented by the formula (2), the addition rate is too high to disperse and the slurry is gelled, which is not preferable. That is, in the present invention, it is important that the range of the formula (2) is satisfied in order to achieve high-concentration, high-dispersion, and efficient slurrying in dry silica slurry.
[0035]
In the present invention, it is extremely important to simultaneously satisfy the dispersion conditions shown in the above formulas (1) and (2). Even if one of the conditions is absent, high concentration, high dispersion, and efficiency are achieved. It cannot be slurried well.
[0036]
The viscosity of the dry silica dispersion is preferably low when used as a coating liquid for inkjet recording materials or OHP coating agents. Therefore, by adopting the method of the present invention, the viscosity of the dry silica slurry obtained during and after the slurrying of the dry silica can be maintained at 1000 mPa · s, particularly 500 mPa · s or less. This makes it possible to produce a dry silica dispersion suitable for use in the coating liquid.
[0037]
In the present invention, when dry silica is slurried, the higher the concentration of dry silica, the more heat generated by dispersion. Therefore, the temperature when slurrying dry silica is in the range of 15 ° C to 40 ° C. It is preferable to carry out while maintaining the same. As a method for maintaining the temperature, there is a method in which a heating or cooling jacket is installed in the dispersion tank to keep the temperature constant.
[0038]
【The invention's effect】
As understood from the above description, the method for dispersing a dry slurry of the present invention can be slurried by dispersing dry silica in a polar solvent efficiently at a high concentration, high dispersion, and This is an extremely industrially useful method.
[0039]
The obtained dry silica slurry is treated with a further disperser as necessary to obtain a dry silica dispersion, which can be suitably used, for example, as a raw material for a coating liquid for inkjet recording sheets.
[0040]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
[0041]
In addition, in order to evaluate the dispersion state of dry silica, it carried out by the following method.
[0042]
(Evaluation of dispersion state of dry silica)
The visible light absorption spectrum of the treatment liquid was measured using a spectrophotometer (manufactured by JASCO). First, using a cell having an optical path length of 10 mm, the reference cell and the sample cell were each filled with ion-exchanged water, and zero point calibration was performed over the entire wavelength range. Next, dilute with ion-exchanged water so that the concentration of the treatment solution is 1.5% by weight, put the diluted solution in the sample cell, and measure the absorbance (τ) in the measurement wavelength (λ) range of 460 to 700 nm. did. Log (λ) and log (τ) were plotted, and the slope (−n) of the straight line was obtained by the least square method using the following equation (4).
[0043]
τ = αλ− ⁿ (4)
N thus obtained is called a light scattering index, and was adopted as an index indicating the dispersion state of dry silica in the present invention. The higher n, the better the dispersion state of dry silica.
[0044]
(Measurement of viscosity)
300 g of dry silica slurry was collected in a 500 cc container, and the viscosity of the slurry was measured using a B-type viscometer (manufactured by Tokimec, BL) at 60 rpm.
[0045]
Example 1
Under the dispersion conditions of dry silica, the peripheral speed u was set to 9.4 (m / sec), and the discharge amount Q was set to 0.61 (kg / sec). After 1600 g of ion-exchanged water was previously charged in the dispersion tank, slurrying was performed with an ultra mixer (manufactured by Mizuho Kogyo) while adding 500 g of dry silica powder (Leosil QS30, manufactured by Tokuyama) having a specific surface area of 300 m ² / g to the dispersion tank. went. The addition rate v / W at this time was 2.1 × 10 ⁻⁴ (1 / second), and d / D was 0.30. Table 1 shows the dispersion conditions, and Table 2 shows the physical properties of the obtained dry silica slurry. The dispersion energy (Q × u ² / W) at this time was 33.7 (J / kg / second), and the dispersion energy and the addition rate were within the ranges of the formulas (1) and (2). The n value of the obtained dry silica slurry was 2.7, and the dispersion state of the dry silica was good.
[0046]
Comparative Example 1
The peripheral speed u is 4.7 (m / sec), the discharge amount Q is 0.30 (kg / sec), the addition speed v / W is 5.6 × 10 ⁻⁵ (1 / sec), and dry silica is added. Slurry was performed in the same manner as in Example 1 except that the amount was changed to 300 g. Table 1 shows the dispersion conditions, and Table 2 shows the physical properties of the obtained dry silica slurry. The dispersion energy (Q × u ² / W) at this time was 4.2 (J / kg / second), and the dispersion energy was smaller than the range of the formula (1). Therefore, the n value of the obtained dry silica slurry was It was 1.7, and the dispersion state of dry silica was bad.
[0047]
Comparative Example 2
Except for changing the peripheral speed u to 18.8 (m / sec), the discharge amount Q to 1.22 (kg / sec), and the addition speed v / W to 4.7 × 10 ⁻⁴ (1 / sec), Slurry similar to Example 1 was performed. After the start of dry silica addition, the dry silica powder was quickly taken into the ion-exchanged water, but when the amount of dry silica powder added reached 480 g, the fluidity suddenly deteriorated and the entire slurry gelled. The target amount of 500 g could not be added. The dispersion energy (Q × u ² / W) at this time was 269.5 (J / kg / second), and the dispersion energy was larger than the range of the formula (1).
[0048]
Example 2
Under the dry silica dispersion conditions, the peripheral speed u was set to 18.3 (m / sec), and the discharge amount Q was set to 7.00 (kg / sec). 200 kg of ion-exchanged water is charged in a dispersion tank in advance, and then slurryed with an ultra mixer (manufactured by Mizuho Kogyo) while adding 50 kg of dry silica (Leosil QS30, manufactured by Tokuyama) with a specific surface area of 300 m ² / g to the dispersion tank. It was. The addition rate v / W at this time was 1.1 × 10 ⁻⁴ (1 / second), and d / D was 0.13. Table 1 shows the dispersion conditions, and Table 2 shows the physical properties of the obtained dry silica slurry. The dispersion energy (Q × u ² / W) at this time was 11.7 (J / kg / second), and the dispersion energy and the addition rate were within the ranges of the formulas (1) and (2). The n value of the obtained dry silica slurry was 2.8, and the dispersion state of the dry silica was good.
[0049]
Comparative Example 3
Slurry similar to that of Example 2 was performed except that the addition rate v / W was changed to 4.2 × 10 ⁻⁴ (1 / second). The dry silica powder was quickly taken into the ion-exchanged water, but when the amount of dry silica powder added reached 40 kg, the fluidity suddenly deteriorated and the entire slurry gelled. Could not be added. The dispersion energy (Q × u ² / W) at this time was 11.7, and the addition rate of dry silica was larger than the range of formula (2).
[0050]
Example 3
Under the dispersion conditions of dry silica, the peripheral speed u was set to 10.6 (m / sec), and the discharge amount Q was set to 0.68 (kg / sec). After 2400 g of ion-exchange water was previously charged in the dispersion tank, slurrying was performed with an ultra mixer (manufactured by Mizuho Kogyo Co., Ltd.) while adding 600 g of dry silica powder having a specific surface area of 90 m ² / g (Reorosil QS09, manufactured by Tokuyama) to the dispersion tank. went. The addition rate v / W at this time was 2.3 × 10 ⁻⁴ (1 / second) and d / D = 0.24. Table 1 shows the dispersion conditions, and Table 2 shows the physical properties of the obtained dry silica slurry. The dispersion energy (Q × u ² / W) at this time was 32.0 (J / kg / second), and the dispersion energy and the addition rate were within the ranges of the formulas (1) and (2). The n value of the obtained dry silica slurry was 3.0, and the dispersion state of dry silica was good.
[0051]
Example 4
Under the dry silica dispersion conditions, the peripheral speed u was set to 11.0 (m / sec), and the discharge amount Q was set to 0.63 (kg / sec). After 1600 g of ion-exchanged water was previously charged in the dispersion tank, slurrying was performed with a homogenizer (manufactured by IKA) while adding 400 g of dry silica powder having a specific surface area of 300 m ² / g (Leosil QS30, manufactured by Tokuyama) to the dispersion tank. . At this time, the addition rate v / W was set to 1.7 × 10 ⁻⁴ (1 / second), and d / D was set to 0.20. Table 1 shows the dispersion conditions, and Table 2 shows the physical properties of the obtained dry silica slurry. The dispersion energy (Q × u ² / W) at this time was 32.0 (J / kg / second), and the dispersion energy and the addition rate were within the ranges of the formulas (1) and (2). The n value of the obtained dry silica slurry was 2.5, and the dispersion state of the dry silica was good.
[0052]
Example 5
Under the dry silica dispersion conditions, the peripheral speed u was set to 15.7 (m / sec), and the discharge amount Q was set to 3.38 (kg / sec). 40 kg of ion-exchanged water is charged in the dispersion tank in advance, and 10 kg of dry silica (Leosil QS30, manufactured by Tokuyama) having a specific surface area of 300 m ² / g is added to the dispersion tank, while 1 ultramixer, 1 propeller mixer, and anchor Slurry was performed by a combination type disperser (manufactured by Mizuho Kogyo Co., Ltd.) equipped with one unit. At this time, the addition rate v / W was set to 1.2 × 10 ⁻⁴ (1 / second) and d / D = 0.12. The dispersion conditions are shown in Table 1, and the dry silica slurry obtained at this time The physical properties are shown in Table 2. The dispersion energy (Q × u ² / W) at this time was 20.8 (J / kg / second), and the dispersion energy and the addition rate were within the ranges of the formulas (1) and (2). The n value of the obtained dry silica slurry was 2.6, and the dispersion state of the dry silica was good.
[0053]
Comparative Example 4
Under the dispersion conditions of dry silica, the peripheral speed u was set to 16.5 (m / sec), and the discharge amount Q was set to 1.06 (kg / sec). First, 1280 g of ion-exchanged water is charged into the dispersion tank, and then slurryed by an ultra mixer (manufactured by Mizuho Kogyo Co., Ltd.) while adding 340 g of dry silica having a specific surface area of 300 m ² / g (Reorosil QS30, manufactured by Tokuyama) to the dispersion tank. It was. The addition rate v / W at this time was 4.2 × 10 ⁻⁴ (1 / second) and d / D = 0.32. Table 1 shows the dispersion conditions, and Table 2 shows the physical properties of the obtained dry silica slurry. The dispersion energy (Q × u ² / W) at this time was 225.7 (J / kg / second), and the dispersion energy was larger than the range of the formula (1). 1 and the dispersion state of the dry silica was poor, and the dry silica slurry had a high viscosity.
[0054]
[Table 1]

[0055]
[Table 2]

[0056]
As seen in Tables 1 and 2, by adjusting the peripheral speed of the turbine, the discharge rate, the addition rate of dry silica, and the weight of the polar solvent to the ranges satisfying the expressions (1) and (2) simultaneously, A dry silica slurry with good dry silica dispersion and low viscosity was obtained.
[0057]
In addition, the dry silica slurry obtained in Examples 1 to 5 in which the dry silica was slurried within the range indicated by the formulas (1) and (2) was a dry silica slurry outside the range of the formula (1). Compared to the dry silica slurry obtained in Comparative Examples 1 and 4 where the conversion was performed, the n value was high, the dispersion state was good, and the viscosity was low. Moreover, with respect to Comparative Example 2 in which the dry silica was slurried out of the range indicated by the formula (1) and Comparative Example 3 in which the dry silica was slurried out of the range of the formula (2), the target dry type The entire slurry gelled before reaching the silica concentration.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a typical structure of a high-speed rotary shearing disperser used in the present invention.
1 Stator 2 Turbine 3 Dispersion tank

Claims (2)

Using a high-speed rotary shearing disperser in which the ratio (d / D) of the turbine diameter (d) to the dispersion tank inner diameter (D) is 0.05 to 0.5, dry silica is added to the polar solvent. A method of dispersing, wherein the peripheral speed (u; m / sec) of the turbine of the high-speed rotary shear type disperser, the discharge rate of the turbine (Q; kg / sec), the addition rate of dry silica (v: kg / sec) And dry silica dispersion under conditions where the weight (W; kg) of the polar solvent satisfies the formulas (1) and (2) at the same time.
5 ≦ (Q × u ² / W) ≦ 200 (1)
A ≦ (v / W) ≦ B (2)

The method for dispersing dry silica according to claim 1, wherein the dry silica is added until the silica concentration in the polar solvent becomes 10 to 35% by weight.

Images