JP3595686B2 - Heavy calcium carbonate slurry and its preparation method - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、重質炭酸カルシウム、特に塗工紙塗料用に好適な白色顔料として大量に使用される重質炭酸カルシウム、及びその調製方法に関するものである。
【従来の技術】
塗工用無機顔料として、カオリン、重質炭酸カルシウム、沈降性炭酸カルシウム、酸化チタンなどが幅広く使用されている。これらの白色顔料は、白紙光沢、白色度、不透明度、平滑、インキ受理性など塗工紙の光学的性質及び印刷適正に大きな影響を及ぼす。これらの白色顔料のうち、重質炭酸カルシウムは、沈降性炭酸カルシウムに比べて粒子径が大きく粒度分布の幅も広いが、安価で流動性に優れており、紙用塗料に多く配合される傾向にある。紙用塗料として用いる場合、炭酸カルシウムの顔料としての性能は粒子径によって大きく変化し、０．２〜５μｍの範囲では粒子径は小さくなるにつれて、不透明度、白色度、光沢、インキ受理性は向上するが、０．２μｍ以下になると不透明度と白色度も低下する。
近年、重質炭酸カルシウムについても粒径の小さい製品が提供されているが、単に機械的粉砕をしただけでは粒子径が小さくなるにつれて０．２μｍ以下の粒子の量が増加し、これにより流動性の低下をもたらし、又比表面積の増大に伴い塗工カラーのバインダーの要求量が増え塗工紙の光学特性に悪影響を与えるなど問題も多い。
【０００２】
一般的に、重質炭酸カルシウムは天然の石灰石を機械的に粉砕することによって製造されている。調製方法には乾式粉砕と湿式粉砕があり、乾式粉砕品は空気分級により粒度を調整している。近年、高性能な分級機の開発により粗粒子の除去の精度は向上しているが、粒径が小さくなるにつれて粒子の凝集力が強くなり０．２μｍ以下の微粒子を分離することは困難である。湿式粉砕においても原料粒度や粉砕条件の制御により粗粒子と微粒子の少ない調製方法が提供されているが、この方法とて十分とはいえない。
一方、スラリー中の粗粒の除去には工業的には振動スクリーンが使用されているが、スクリーンの開目は４５μｍ程度であるので粗粒子の混入が避けられない。粒径が２０μｍよりも大きい粗粒子の混入は、高速塗工において問題となる。例えば、高速塗工に伴い、ブレード圧が上がる為塗料中の水分が原紙に吸収され流動性不良となり、ストリークを引き起こす原因となったり、又リターンカラーの顔料の粒度分布がブロードとなり操業時間とともにカラーの粒度分布をブロードにし、紙質を変化させる要因となっている。
【０００３】
【発明が解決しようとする課題】
本発明は、２０μｍよりも大きい粗粒子の含有量及び０．２μｍ以下の微粒子の含有量が少なく、特に塗工紙塗料用に好適に用いられる重質炭酸カルシウム水性スラリーを提供することを目的とする。
本発明は、又、このような重質炭酸カルシウム水性スラリーの効率的な調製方法を提供することを目的とする。
【課題を解決するための手段】
本発明は、特定の高濃度の重質炭酸カルシウム水性スラリーを、特定の条件下で連続的に遠心分離すると２０μｍよりも大きい粗粒子（６３５メッシュオン）を効率的に除去することができ、及び／又はこの分離された水性スラリーを希釈して別の条件で連続的に遠心分離すると０．２μｍ以下の微粒子を効率的に除去することができ、これにより上記課題を効率的に解決できるとの知見に基づいてなされたのである。
【０００４】
すなわち、本発明は、重質炭酸カルシウムの平均粒径が０．５〜２μｍ、固形分濃度が７３〜８５重量％、液温２０℃における粘度が１５０ｍＰａｓ以下である重質炭酸カルシウム水性スラリーであって、該スラリーに含まれる重質炭酸カルシウムのＢＥＴ比表面積が６〜１２ｍ２／ｇ、粒度分布測定曲線の５０重量％の粒子径と粒度分布測定曲線の１０重量％の粒子径の比（Ｄ５０／Ｄ１０）が１．５〜２．５であり、かつ粒径が２０μｍより大きい重質炭酸カルシウムの含有量が４０ｐｐｍ以下であることを特徴とする重質炭酸カルシウム水性スラリーを提供する。
本発明は、又、重質炭酸カルシウムの平均粒径が０．５〜２μｍ、固形分濃度が７４〜８０重量％であって、粘度が３００ｍＰａｓ以下の重質炭酸カルシウム水性スラリーを遠心分離機に連続的に導入して、下記の式で表される遠心効果Ｚが２００〜３０００の範囲内で、重液と軽液とに、遠心分離前の水性スラリーの固形分濃度と遠心分離後の軽液の固形分濃度の差が１重量％以下となるように連続的に遠心分離し、軽液を回収し、この軽液に水を加えて固形分濃度を３０〜７０重量％、粘度を１００ｍＰａｓ以下に調製し、この重質炭酸カルシウム水性スラリーを遠心分離機に連続的に導入して、遠心効果Ｚが１０００〜３０００の範囲で、連続的に重液と軽液とに、遠心分離し、重液を回収することを特徴とする、上記特性の重質炭酸カルシウム水性スラリーの調製方法を提供する。
【０００５】
【式１】
Ｚ＝（Ｎ２ π２ ｒ）／（９００ｇ）
（式中、Ｎは回転数［ｒｐｍ］ 、ｒは転半径［ｍ］ 、ｇは重力加速度［ｍ／ｓｅｃ２ ］ を表す。）
【発明の実施の形態】
本発明で原料として用いる重質炭酸カルシウムスラリーは、天然石灰石を乾式粉砕し得られた粉体に水と分散剤とを添加して水に分散させたものを用いられる。特に、このようにして調製した水性スラリーを、さらに、ビーズミル等を用い湿式粉砕したものが好ましい。
【０００６】
本発明では、天然石灰石を直ちに湿式粉砕することができるが、湿式粉砕に先立って、予めを乾式粉砕するのがよい。乾式粉砕では、石灰石の粒径を４０ｍｍ以下、好ましくは平均粒径を２ｍｍ〜２μｍ程度に粉砕しておくのがよい。
本発明では、次に、上記粉砕した石灰石の表面に有機分散剤が施すのがよい。これは種々の方法で行うことができるが、乾式粉砕した石灰石を有機分散剤の存在下で湿式粉砕することにより行うのが好ましい。
具体的には、石灰石／水性媒体（好ましくは水）との重量比が３０／７０〜８５／１５、好ましくは６０／４０〜８０／２０の範囲となるように石灰石に水性媒体を加え、ここに分散剤を加える。使用する分散剤の量は特に限定されないが、重質炭酸カルシウム１００重量部当たり固形分として０．１〜２．０重量部用いるのが好ましく、より好ましくは０．３〜１．０重量部添加し、常法により湿式粉砕する。又は、上記範囲の量となる分散剤を予め溶解してなる水性媒体を石灰石と混合し、常法により湿式粉砕する。湿式粉砕は、バッチ式でも連続式でもよく、サンドミル、アトライター、ボールミルなどの粉砕媒体を使用したミルなどが使用するのが好ましい。このように湿式粉砕することにより、平均粒径が２μｍ 以下、好ましくは平均粒径２〜０．５μｍ 、より好ましくは平均粒径１．５〜０．５μｍ のものが得られる。又、液温２０℃における粘度を３００ｍＰａｓ以下に調整したものが好ましく、特に５０〜２００ｍＰａｓに調整したものが好ましい。
【０００７】
ここで、分散剤としては、水溶性カチオン系界面活性剤（Ａ）、水溶性アニオン系界面活性剤（Ｂ）および水溶性非イオン系界面活性剤（Ｃ）があげられる。
有機分散剤として用いる水溶性カチオン系界面活性剤（Ａ）としては、第１、２、３級アミン塩型カチオン系低分子または高分子界面活性剤および第４級アンモニウム塩型カチオン系低分子または高分子界面活性剤が挙げられる。
第１〜３級アミン塩型低分子界面活性剤としては、例えば高級アルキルアミン塩、高級アルキルアミンエチレンオキサイド付加物、高級アルキルアミンエチレンオキサイド／プロピレンオキサイド付加物、ソロミンＡ型アミン塩、サパミンＡ型アミン塩、アーコベルＡ型アミン塩およびイミダゾリン型アミン塩等が挙げられる。
第４級アンモニウム塩型低分子界面活性剤としては、例えば高級アルキルトリメチルアンモニウム塩、アルキルジメチルベンジルアンモニウム塩、サパミン型第４級アンモニウム塩、イミダゾリン型第４級アンモニウム塩およびアルキルビリジウム塩等が挙げられる。
【０００８】
第１〜３級アミン塩型高分子界面活性剤としては、例えばポリエチレンイミン、ポリアルキレンポリアミン塩、ポリアミン・ジシアンジアミド縮合塩、ポリジアリルアミン塩等が挙げられ、第４級アンモニウム塩型高分子界面活性剤としては、例えばポリスチレンメチルアミノトリメチルアンモニウム塩、ポリジアリルジメチルアンモニウム塩、トリメチルアミノエチル（メタ）アクリレートアンモニウム塩およびポリＮ−アルキルピリジン塩等が挙げられる。
これらのカチオン系界面活性剤の内、湿式粉砕時に高濃度スラリーを得るためには、アミン塩型高分子界面活性剤または第４級アンモニウム塩型高分子界面活性剤が好ましいが、特に好ましいものとしてジアリルアミンの単独またはビニール化合物との共重合物の塩およびポリジアリルジメチルアンモニウム塩が挙げられる。このような高分子分散剤としては、特開平７−３００５６８号公報に記載の水溶性カチオン性コポリマー分散剤が好ましい。特開平７−３００５６８号公報における該水溶性カチオン性コポリマー分散剤の記載は、本明細書の記載に含まれるものとする。これらの分子量は、特に限定はないが、好ましくは１０００〜１５００００であり、更に好ましくは５０００〜８００００である。
【０００９】
有機分散剤として用いる水溶性界面活性剤（Ｂ）としては、官能基としてカルボン酸塩、硫酸エステル塩、スルホン酸塩およびリン酸エステル塩を持つ低分子または高分子界面活性剤が挙げられる。
低分子カルボン酸塩としては、例えばラウリン酸ナトリウム、ステアリン酸ナトリウムおよびオレイン酸ナトリウム等の高級脂肪酸塩、高級アルコールポリエチレンオキサイドエーテル酢酸塩、ペルフルオロアルキルカルボン酸塩等が挙げられ、高分子カルボン酸塩としては、例えばポリアクリル酸塩、ポリアクリル酸−マレイン酸共重合物の塩等のカルボン酸単量体の単独または少なくとも２つ以上からなる共重合物またはその塩、ビニル化合物とカルボン酸系単量体との共重合物またはその塩およびカルボキシメチルセルロース等が挙げられる。
低分子硫酸エステル塩としては、例えば高級アルコールポリエチレンオキサイド硫酸エステル塩、硫酸化油、硫酸化脂肪酸エステル、硫酸化脂肪酸、硫酸化オレフィンおよびアルキルフェノールポリエチレンオキサイド硫酸エステル塩等が挙げられる。
【００１０】
低分子スルホン酸塩としては、例えばアルキルベンゼンスルホン酸塩、α−オレフィンスルホン酸塩、アルカンポリスルホン酸塩、ペルフルオロアルキルスルホン酸塩、イゲホンＴ型およびエアロゾル型等が挙げられ、高分子スルホン酸塩としては、ナフタレンスルホン酸塩のホルマリン縮合物、ポリスチレンスルホン酸塩、ポリビニルスルホン酸塩、ポリアリールスルホン酸塩およびアクリルアミドとアクリルアミドプロパンスルホン酸の共重合物の塩等が挙げられる。
共重合型高分子界面活性剤としては、例えばカルボン酸単量体とスルホン酸単量体からなる共重合体またはその塩が挙げられる。
低分子リン酸エステル塩としては、例えば高級アルコールモノリン酸エステル塩、高級アルコールポリエチレンオキサイドリン酸エステル塩およびアルキルフェノールポリエチレンオキサイドリン酸エステル塩等が挙げられる。
【００１１】
これらのアニオン系界面活性剤の内、湿式粉砕時に高濃度スラリーを得るためには、高分子型界面活性剤が好ましいが、特に好ましいものとして、ポリアクリル酸またはその塩、ポリアクリル酸−マレイン酸共重合物またはその塩等のカルボン酸単量体の単独または少なくともそれらの２つ以上からなる共重合物またはその塩が挙げられる。これらの分子量は、特に限定はないが、好ましくは１０００〜１０００００であり、更に好ましくは５０００〜５００００である。
有機分散剤として使用する水溶性界面活性剤（Ｃ）としては、ポリエチレングリコール型および多価アルコール型非イオン界面活性剤が挙げられる。
ポリエチレングリコール型としては、例えば高級アルコールエチレンオキサイド付加物、アルキルフェノールエチレンオキサイド付加物、脂肪酸エチレンオキサイド付加物、多価アルコール脂肪酸エステルエチレンオキサイド付加物、脂肪酸アミドエチレンオキサイド付加物、ポリプロピレングリコールエチレンオキサイド付加物およびポリエーテル変成シリコーン等が挙げられる。
【００１２】
多価アルコール型としては、例えばグリセロールの脂肪酸エステル、ペンタエリスリトールの脂肪酸エステル、ソルビトールおよびソルビタンの脂肪酸エステル、ショ糖の脂肪酸エステル、多価アルコールのアルキルエーテル、ポリグリセリン脂肪酸エステルまたはそのエチレンオキサイド付加物およびアルカノールアミン類の脂肪酸アミド等が挙げられ、更にメチルセルロース（ＭＣ）、ハイドロオキシエチルセルロース（ＨＥＣ）、ポリビニールアルコール（ＰＶＡ）、ポリアルキレンオキサイドビニールエテル化合物およびポリハイドロキシルアルキル（メタ）アクリレート等が挙げられる。
これらの非イオン系界面活性剤の内、湿式粉砕時に高濃度スラリーを得るためには、高分子型界面活性剤が好ましいが、特に好ましいものとして抵重合度の部分ケン化ポパールおよびポリハイドロキシアルキル（メタ）アクリレート等が挙げられる。
上記種々の分散剤のうち、特に、ポリアクリル酸系分散剤（例えばサンノプコ社製：Ｆ―１３０）が好ましい。
【００１３】
本発明では、上記方法において、重質炭酸カルシウム水性スラリー濃度を所定の濃度に調整し、次に遠心分離機を用いる次の方法により、本発明の重質炭酸カルシウム水性スラリーを調製する。
方法１
上記の方法により湿式粉砕した平均粒径が０．５〜２μｍ、固形分濃度が７４〜８０重量％（好ましくは７５〜７７重量％）であって、液温２０℃における粘度が３００ｍＰａｓ以下（より好ましくは２００ｍＰａｓ以下、特に５０〜１５０ｍＰａｓ）の重質炭酸カルシウム水性スラリーを遠心分離機に導入して、下記の式で表される遠心効果Ｚが２００〜３０００（好ましくは５００〜１５００）の範囲で、重液と軽液とに、遠心分離前の水性スラリーの固形分濃度と遠心分離後の軽液の固形分濃度の差が１重量％以下（好ましくは０．２〜０．５重量％）となるように連続的に遠心分離し、粗粒子を含有する重液を除去し、軽液を回収することを特徴とする、固形分濃度が７３〜７９重量％（好ましくは７４〜７６重量％）であって粒径が２０μｍより大きい重質炭酸カルシウムの含有量が４０ｐｐｍ以下（好ましくは２０ｐｐｍ以下）である重質炭酸カルシウム水性スラリーの調製方法。
【式２】
Ｚ＝（Ｎ２ π２ ｒ）／（９００ｇ）
（式中、Ｎは回転数［ｒｐｍ］ 、ｒは転半径［ｍ］ 、ｇは重力加速度［ｍ／ｓｅｃ２ ］ を表す。）
【００１４】
方法２
上記の方法により湿式粉砕した平均粒径が０．５〜２μｍ、固形分濃度が３０〜７０重量％（好ましくは４０〜６０重量％）であって、液温２０℃における粘度が１００ｍＰａｓ以下（好ましくは５０ｍＰａｓ以下、特に１０〜４０ｍＰａｓ）の重質炭酸カルシウム水性スラリーを遠心分離機に導入して、遠心効果Ｚが１０００〜３０００（好ましくは１５００〜３０００）の範囲で、連続的に重液と軽液とに、遠心分離し、微粒子を含有する軽液を除去し、重液を回収することを特徴とする、固形分濃度が７３〜８５重量％（好ましくは７５〜８０重量％）であって、ＢＥＴ比表面積が６〜１２ｍ２／ｇである重質炭酸カルシウム水性スラリーの調製方法。
【００１５】
方法３
上記の方法により湿式粉砕した平均粒径が０．５〜２μｍ、固形分濃度が７４〜８０重量％（好ましくは７５〜７７重量％）であって、液温２０℃における粘度が３００ｍＰａｓ以下（より好ましくは２００ｍＰａｓ以下、特に５０〜１５０ｍＰａｓ）の重質炭酸カルシウム水性スラリーを遠心分離機に導入して、遠心効果Ｚが２００〜３０００（好ましくは５００〜１５００）の範囲で、重液と軽液とに、遠心分離前の水性スラリーの固形分濃度と遠心分離後の軽液の固形分濃度の差が１重量％以下となるように連続的に遠心分離し、粗粒子を含有する重液を除去し、軽液を回収し、次いで、得られた軽液を水で希釈してその固形分濃度を３０〜７０重量％（好ましくは４０〜６０重量％）、粘度を１００ｍＰａｓ以下（好ましくは５０ｍＰａｓ以下、特に１０〜４０ｍＰａｓ）に調製し、この重質炭酸カルシウム水性スラリーを遠心分離機に導入して、遠心効果Ｚが１０００〜３０００（好ましくは１５００〜３０００）の範囲で、連続的に重液と軽液とに、遠心分離し、微粒子を含有する軽液を除去し、重液を回収することを特徴とする、固形分濃度が７３〜８５重量％（好ましくは７５〜８０重量％）であって、ＢＥＴ比表面積が６〜１２ｍ２／ｇである重質炭酸カルシウム水性スラリーの調製方法。
【００１６】
上記遠心分離操作は、遠心分離器に１回または複数回通液して行うことができる。
本発明で用いる遠心分離器は一般に固液分離や分級に用いられるものでよく、例えばデカンタータイプ、バスケットタイプなどの遠心分離器があげられる。このうち、デカンタータイプの遠心分離器が好ましく、この遠心分離機は、排水処理、カオリンの分級等に使用されており、比重差がある２〜５μｍ程度以上の微粒から大粒子の分離や脱水に用いられているが、極微粒子の分離には不適で、許容供給濃度は０．５〜５０重量％といわれている。塗工用に提供される分散性のよい重質炭酸カルシウムスラリーを遠心分離機で処理すると遠心分離機内でハードケーキを作り排出が難しいとされており、従来の技術では高濃度スラリーを供給することは行われていない。本発明では、重質炭酸カルシウムスラリーを高濃度で供給することにより、遠心分離器内での沈降速度をコントロールし、ハードケーキを作ることなくダイラタントなスラリー状態での排出を可能とした。粒度分布は遠心効果、供給液濃度、供給液量を任意に調整することによって任意に制御できる。
【００１７】
【発明の効果】
本発明によれば、２０μｍよりも大きい粗粒子の含有量及び０．２μｍ以下の微粒子の含有量が少ない重質炭酸カルシウム水性スラリーが提供される。又、本発明によれば、このような特性の重質炭酸カルシウム水性スラリーを効率的に調製できる方法が提供される。
本発明により得られた重質炭酸カルシウム水性スラリーは、紙塗工に好適に用いられるが、その用途は紙塗工用に限られず、そのまま又は常法により乾燥してペイント、研磨剤、建材、及びプラスチックやゴムなどの充填剤として使用することができる。
次に本発明を実施例により説明する。
【００１８】
【実施例】
実施例１
平均粒子径８μｍの重質炭酸カルシウム（日本セメント石灰石原料の乾式粉砕品）に水を加え、重質炭酸カルシウム１００重量部当たりアニオン分散剤（ポリアクリル酸系分散剤、サンノプコ社製：Ｆ―１３０）を０．８重量部加え、テーブル式媒体攪拌ミルを用い、直径１．２ｍｍのガラスビーズ充填率１７０％、周速１０ｍ／ｓｅｃ で湿式粉砕し、次いで３５０Ｍｅｓｈスクリーンを通し分級し重質炭酸カルシウム水性スラリーを調製した（平均粒子径１．１０８μｍ、粒径２０μｍ以上１００ｐｐｍ、粒径０．２μｍ以下０．８％、固形分濃度７５．５９重量％、２０℃における粘度１３０ｍＰａｓ）。
この水性スラリーをデカンタータイプの遠心分離器（回転半径０．０７７ｍ、有効体積１．８リットル）に０．３６７ｍ３ ／ｈで供給し、１５００Ｇの遠心力をかけたところ（遠心効果Ｚ１５００）、粗粒が遠心分離器の内壁に沈降した。この沈降した粗粒子をスクリュウによって外部に搬送、排出した。この時、排出された粗粒子を含むスラリー（重液）の濃度は８３．２８重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径１．３９９μｍであった。
【００１９】
一方、遠心分離器から排出された水性スラリー（軽液）の濃度は７５．３９重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径１．０８４μｍ、２０μｍよりも大きい粗粒子の含有量は０．８ｐｐｍであった。尚、遠心分離器からの水性スラリー回収側には適量の水をシャワーリングし、水性スラリーの固形分濃度の調整並びに固化防止を行った。
このようにして得た重質炭酸カルシウム水性スラリーの特性をまとめて表−１に示す。
【００２０】
実施例２
先ず、実施例１と同様の方法により、重質炭酸カルシウム水性スラリーを調製した（平均粒子径１．３４１μｍ、粒径２０μｍ以上４５５ｐｐｍ、粒径０．２μｍ以下０．６９％、固形分濃度７６．２２重量％、２０℃における粘度１２０ｍＰａｓ）。
この水性スラリーを実施例１で用いたのと同じ遠心分離機に０．８２５ｍ３／ｈで供給し、１５００Ｇの遠心力をかけ（遠心効果Ｚ１５００）、実施例１と同様にして粗粒と水性スラリーを回収した。粗粒子を含むスラリー（重液）の濃度は８６．０重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径２．０１８μｍであった。
一方、遠心分離器から排出された水性スラリー（軽液）の濃度は７５．８９重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径１．３２８μｍ、２０μｍよりも大きい粗粒子の含有量は６ｐｐｍであった。
【００２１】
実施例３
先ず、実施例１と同様の方法により、重質炭酸カルシウム水性スラリーを調製した（平均粒子径１．２８４μｍ、粒径２０μｍ以上３７５ｐｐｍ、粒径０．２μｍ以下０．８２％、固形分濃度７３．９３重量％、２０℃における粘度７０ｍＰａｓ）。
この水性スラリーを実施例１で用いたのと同じ遠心分離機に０．５９０ｍ３ ／ｈで供給し、６００Ｇの遠心力をかけ（遠心効果Ｚ６００）、実施例１と同様にして粗粒と水性スラリーを回収した。粗粒子を含むスラリー（重液）の濃度は８５．６３重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径２．０７９μｍであった。
一方、遠心分離器から排出された水性スラリー（軽液）の濃度は７３．５３重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径１．２８４μｍ、２０μｍよりも大きい粗粒子の含有量は１２ｐｐｍであった。
【００２２】
実施例４
先ず、実施例１と同様の方法により、重質炭酸カルシウム水性スラリーを調製した（平均粒子径１．１０４μｍ、粒径２０μｍ以上１０５ｐｐｍ、粒径０．２μｍ以下１．０２％、固形分濃度７６．９５重量％、２０℃における粘度１５０ｍＰａｓ）。
この水性スラリーを実施例１で用いたのと同じ遠心分離機に０．６８４ｍ３ ／ｈで供給し、２１００Ｇの遠心力をかけ（遠心効果Ｚ２１００）、実施例１と同様にして粗粒と水性スラリーを回収した。粗粒子を含むスラリー（重液）の濃度は８４．２３重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径１．３９２μｍであった。
【００２３】
一方、遠心分離器から排出された水性スラリー（軽液）の濃度は７４．９１重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径１．０９６μｍ、２０μｍよりも大きい粗粒子の含有量は３ｐｐｍであった。
このようにして得られた水性スラリーを水で希釈して固形分濃度５６重量％に調整し、前工程で用いたのと同じタイプの遠心分離機に０．１６２ｍ３ ／ｈで供給し、１７００Ｇの遠心力をかけ（遠心効果Ｚ１７００）、実施例１と同様にして重液と軽液とを分離した。軽液の濃度は３６．２８重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径０．３５４μｍであった。
一方、遠心分離器から排出された重液の濃度は７８．４２重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径１．１７４μｍ、０．２μｍよりも小さい微粒子の含有量は０％であった。
【００２４】
実施例５
先ず、実施例１と同様の方法により、重質炭酸カルシウム水性スラリーを調製した（平均粒子径１．１００μｍ、粒径２０μｍ以上９５ｐｐｍ、粒径０．２μｍ以下０．９１％、固形分濃度５８．０重量％、２０℃における粘度３０ｍＰａｓ）。
この水性スラリーを実施例１で用いたのと同じ遠心分離機に０．２５２ｍ３ ／ｈで供給し、１４００Ｇの遠心力をかけ（遠心効果Ｚ１４００）、実施例１と同様にして粗粒と水性スラリーを回収した。粗粒子を含むスラリーの濃度は８０．３５重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径１．３４２μｍであった。
一方、遠心分離器から排出された水性スラリーの濃度は５７．０重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径０．７６２μｍ、２０μｍよりも大きい粗粒子の含有量は０．１ｐｐｍであった。
このようにして得られた水性スラリーを、前工程で用いたのと同じタイプの遠心分離機に０．１６２ｍ３ ／ｈで供給し、２１００Ｇの遠心力をかけ（遠心効果Ｚ２１００）、実施例１と同様にして重液と軽液とを分離した。軽液の濃度は４０．２６重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径０．３６５μｍであった。
【００２５】
一方、遠心分離器から排出された重液の濃度は７８．２９重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径０．８７９μｍ、０．２μｍよりも小さい微粒子の含有量は０．６７％であった。
実施例６
先ず、実施例１と同様の方法により、重質炭酸カルシウム水性スラリーを調製した（平均粒子径１．１００μｍ、粒径２０μｍ以上９５ｐｐｍ、粒径０．２μｍ以下０．９１％、固形分濃度６０．３重量％、２０℃における粘度４５ｍＰａｓ）。
この水性スラリーを実施例１で用いたのと同じ遠心分離機に０．１６２ｍ３ ／ｈで供給し、１７００Ｇの遠心力をかけ（遠心効果Ｚ１７００）、実施例１と同様にして軽液と重液を回収した。軽液の濃度は４９．１２重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径０．５１２μｍであった。
一方、遠心分離器から排出された重液の濃度は７７．５８重量％であり、この中に含まれる重質炭酸カルシウムの平均粒子径１．２４９μｍ、０．２μｍよりも小さい微粒子の含有量は０％であった。
実施例１〜６に記載の特性及び得られたスラリー及び市販品Ａ及びＢの特性を以下の方法で測定した。
【００２６】
粘度
水性スラリーの温度を２０℃に調整した後、東京計器社製：Ｂ型粘度計、スピンドル＃２、ローター回転数６０ｒｐｍ で測定した。
固形分濃度
１０５±５℃での絶乾重量を求め固形分濃度を算出した。
ＢＥＴ比表面積測定方法
ＢＥＴ比表面積測定装置：湯浅アイオニクス社製：モノソープ型で測定した。粒度分布
レーザー回折式粒度分布測定装置：日機装社製：Ｍｉｃｒｏｔｒａｃ Ｘ−１００ で測定した。得られた粒度分布測定曲線の５０重量％の粒子径を平均粒子径とし、又粒度分布測定曲線の５０重量％の粒子径と粒度分布測定曲線の１０重量％の粒子径の比をＤ５０／Ｄ１０として求めた。尚、粒度分布の幅が狭い程、この比率は１に近づく。
実施例１〜３で得られたスラリーの特性を表―１に、実施例４〜６で得られたスラリーと市販品Ａ及びＢの特性を表−２に示す。
【００２７】
【表１】
表−１
【表２】
表−２
表―２の粒度分布を制御した本発明の重質炭酸カルシウムスラリーはＤ５０／Ｄ１０とＢＥＴ比表面積が従来品に比べ小さく微粒子が除去されていることがわかる。例えば市販品Ｂは光沢向上を目的に提供されているが、一般に使用されている市販品Ａに比べ比表面積が大きくバインダー等の必要量が増加し塗工紙の光学特性に悪影響を与える。しかし、本発明品の実施例５では市販品Ａに比べ平均粒子径が小さいにも関わらず、ＢＥＴ比表面積も小さく、バインダーの必要量も少なく塗工紙の光学特性に良好な影響を与えることができる。また、市販品は微粒化に伴い製品の白色度が低下するが、本発明品は０．２μｍ以下の微粒子を除去したため、白色度も向上している。
【図面の簡単な説明】
【図１】市販品Ａの粒度分布曲線を示す。
【図２】市販品Ｂの粒度分布曲線を示す。
【図３】実施例４で得られた重質炭酸カルシウム水性スラリーの粒度分布曲線を示す。
【図４】実施例５で得られた重質炭酸カルシウム水性スラリーの粒度分布曲線を示す。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to heavy calcium carbonate, particularly heavy calcium carbonate used in large quantities as a white pigment suitable for a coated paper coating, and a method for preparing the same.
[Prior art]
As the coating inorganic pigment, kaolin, heavy calcium carbonate, precipitated calcium carbonate, titanium oxide and the like are widely used. These white pigments greatly affect the optical properties of coated paper such as white paper gloss, whiteness, opacity, smoothness, ink acceptability, and printability. Among these white pigments, heavy calcium carbonate has a large particle size and a wide range of particle size distribution as compared with precipitated calcium carbonate, but it is inexpensive and has excellent fluidity, and tends to be widely used in paper coatings. It is in. When used as a paper coating, the performance of calcium carbonate as a pigment varies greatly depending on the particle size. In the range of 0.2 to 5 μm, the opacity, whiteness, gloss, and ink receptivity improve as the particle size decreases. However, when the thickness is 0.2 μm or less, the opacity and whiteness also decrease.
In recent years, products having a small particle size have been provided also for heavy calcium carbonate. However, merely by mechanical pulverization, as the particle size decreases, the amount of particles of 0.2 μm or less increases. In addition, the required amount of the binder for the coating color increases with an increase in the specific surface area, and there are many problems such as adversely affecting the optical characteristics of the coated paper.
[0002]
Generally, heavy calcium carbonate is produced by mechanically grinding natural limestone. The preparation method includes dry pulverization and wet pulverization, and the particle size of the dry pulverized product is adjusted by air classification. In recent years, the development of high-performance classifiers has improved the accuracy of removing coarse particles, but as the particle size decreases, the cohesive force of the particles increases and it is difficult to separate fine particles of 0.2 μm or less. . In the wet pulverization, a method for preparing less coarse particles and fine particles is provided by controlling the raw material particle size and pulverization conditions, but this method is not sufficient.
On the other hand, a vibrating screen is industrially used for removing coarse particles in the slurry, but since the opening of the screen is about 45 μm, mixing of coarse particles is inevitable. Mixing of coarse particles having a particle size larger than 20 μm is a problem in high-speed coating. For example, as the blade pressure increases with high-speed coating, the moisture in the paint is absorbed by the base paper, resulting in poor fluidity, causing streak, and the particle size distribution of the pigment of the return color becomes broad, and the color increases with operating time. Is broadened, which is a factor that changes the paper quality.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to provide a heavy calcium carbonate aqueous slurry that has a low content of coarse particles larger than 20 μm and a low content of fine particles of 0.2 μm or less, and is particularly preferably used for coated paper coatings. I do.
Another object of the present invention is to provide a method for efficiently preparing such an aqueous slurry of heavy calcium carbonate.
[Means for Solving the Problems]
The present invention is capable of efficiently removing coarse particles (635 mesh on) larger than 20 μm when a specific high-concentration aqueous calcium carbonate aqueous slurry is continuously centrifuged under specific conditions, and If the separated aqueous slurry is diluted and continuously centrifuged under another condition, the fine particles having a particle size of 0.2 μm or less can be efficiently removed, whereby the above problem can be efficiently solved. It was based on knowledge.
[0004]
That is, the present invention provides an aqueous calcium carbonate slurry having an average particle size of heavy calcium carbonate of 0.5 to 2 μm, a solid content of 73 to 85% by weight, and a viscosity at a liquid temperature of 20 ° C. of 150 mPas or less. The heavy calcium carbonate contained in the slurry has a BET specific surface area of 6 to 12 m.2/ G, the ratio of the particle size of 50% by weight of the particle size distribution measurement curve to the particle size of 10% by weight of the particle size distribution measurement curve (D50/ D10) Is 1.5 to 2.5, and the content of heavy calcium carbonate having a particle size of more than 20 μm is 40 ppm or less.
The present invention also provides a heavy calcium carbonate aqueous slurry having an average particle size of 0.5 to 2 μm, a solid content of 74 to 80% by weight, and a viscosity of 300 mPas or less to a centrifuge. Continuously introduced, the centrifugal effect Z represented by the following formula is within the range of 200 to 3000, and the heavy liquid and the light liquid are separated into the solid content concentration of the aqueous slurry before centrifugation and the light concentration after centrifugation. The liquid is continuously centrifuged so that the difference in the solid concentration of the liquid is 1% by weight or less, the light liquid is collected, and water is added to the light liquid to give a solid concentration of 30 to 70% by weight and a viscosity of 100 mPas. Prepared below, this heavy calcium carbonate aqueous slurry is continuously introduced into a centrifuge, and the centrifugal effect Z is in the range of 1000-3000, and continuously centrifuged into heavy liquid and light liquid, Heavy carbonic acid having the above characteristics, characterized by recovering heavy liquid To provide a process for the preparation of calcium aqueous slurry.
[0005]
(Equation 1)
Z = (N2π2r) / (900g)
(Where N is the number of revolutions [rpm], r is the radius of gyration [m], g is the gravitational acceleration [m / sec]2]. )
BEST MODE FOR CARRYING OUT THE INVENTION
The heavy calcium carbonate slurry used as a raw material in the present invention is obtained by adding water and a dispersant to a powder obtained by dry pulverizing natural limestone and dispersing the powder in water. In particular, the aqueous slurry prepared in this manner is further preferably subjected to wet pulverization using a bead mill or the like.
[0006]
In the present invention, natural limestone can be wet-pulverized immediately, but it is preferable to dry-pulverize the natural limestone before the wet pulverization. In the dry pulverization, the limestone is preferably pulverized to a particle size of 40 mm or less, preferably an average particle size of about 2 mm to 2 μm.
Next, in the present invention, an organic dispersant is preferably applied to the surface of the crushed limestone. Although this can be performed by various methods, it is preferable that the dry-ground limestone is wet-ground in the presence of an organic dispersant.
Specifically, the aqueous medium is added to the limestone so that the weight ratio with the limestone / aqueous medium (preferably water) is in the range of 30/70 to 85/15, preferably 60/40 to 80/20. Add the dispersant. The amount of the dispersant to be used is not particularly limited, but it is preferable to use 0.1 to 2.0 parts by weight, more preferably 0.3 to 1.0 part by weight, as a solid content per 100 parts by weight of heavy calcium carbonate. Then, wet pulverization is performed by a conventional method. Alternatively, an aqueous medium in which a dispersant having an amount in the above range is dissolved in advance is mixed with limestone, and wet-pulverized by a conventional method. The wet pulverization may be a batch type or a continuous type, and it is preferable to use a mill using a pulverizing medium such as a sand mill, an attritor, and a ball mill. By such wet pulverization, a powder having an average particle size of 2 μm or less, preferably 2 to 0.5 μm, more preferably 1.5 to 0.5 μm is obtained. Further, those whose viscosity at a liquid temperature of 20 ° C. is adjusted to 300 mPas or less are preferable, and those whose viscosity is adjusted to 50 to 200 mPas are particularly preferable.
[0007]
Here, examples of the dispersant include a water-soluble cationic surfactant (A), a water-soluble anionic surfactant (B), and a water-soluble nonionic surfactant (C).
Examples of the water-soluble cationic surfactant (A) used as an organic dispersant include primary, secondary and tertiary amine salt type cationic low molecular weight or high molecular weight surfactants and quaternary ammonium salt type cationic low molecular weight or Polymeric surfactants.
Examples of the primary to tertiary amine salt type low molecular surfactants include higher alkylamine salts, higher alkylamine ethylene oxide adducts, higher alkylamine ethylene oxide / propylene oxide adducts, solomin A type amine salts, and sapamin A type. An amine salt, an Arkover A type amine salt, an imidazoline type amine salt and the like can be mentioned.
Examples of the quaternary ammonium salt type low molecular surfactant include higher alkyltrimethylammonium salt, alkyldimethylbenzylammonium salt, sapamin type quaternary ammonium salt, imidazoline type quaternary ammonium salt, and alkylpyridium salt. Can be
[0008]
Examples of the primary to tertiary amine salt type polymer surfactants include polyethyleneimine, polyalkylene polyamine salts, polyamine / dicyandiamide condensed salts, and polydiallylamine salts, and quaternary ammonium salt type polymer surfactants. Examples thereof include polystyrene methylaminotrimethylammonium salt, polydiallyldimethylammonium salt, trimethylaminoethyl (meth) acrylate ammonium salt and polyN-alkylpyridine salt.
Among these cationic surfactants, amine salt-type polymer surfactants or quaternary ammonium salt-type polymer surfactants are preferable in order to obtain a high-concentration slurry at the time of wet pulverization. Salts of diallylamine alone or copolymers with vinyl compounds and polydiallyldimethylammonium salts are included. As such a polymer dispersant, a water-soluble cationic copolymer dispersant described in JP-A-7-300568 is preferable. The description of the water-soluble cationic copolymer dispersant in JP-A-7-300568 is included in the description of the present specification. These molecular weights are not particularly limited, but are preferably 1,000 to 150,000, and more preferably 5,000 to 80,000.
[0009]
Examples of the water-soluble surfactant (B) used as the organic dispersant include low-molecular or high-molecular surfactants having a carboxylate, a sulfate, a sulfonate, and a phosphate as a functional group.
Examples of the low molecular carboxylate include higher fatty acid salts such as sodium laurate, sodium stearate and sodium oleate, higher alcohol polyethylene oxide ether acetate, perfluoroalkyl carboxylate, and the like. Is, for example, a carboxylic acid monomer such as a polyacrylate, a salt of a polyacrylic acid-maleic acid copolymer alone or a copolymer comprising at least two or more salts thereof, a vinyl compound and a carboxylic acid monomer And a carboxymethylcellulose and a copolymer thereof with a body or a salt thereof.
Examples of the low-molecular sulfate ester salts include higher alcohol polyethylene oxide sulfate salts, sulfated oils, sulfated fatty acid esters, sulfated fatty acids, sulfated olefins, and alkylphenol polyethylene oxide sulfate salts.
[0010]
Examples of the low molecular sulfonate include alkylbenzene sulfonate, α-olefin sulfonate, alkane polysulfonate, perfluoroalkyl sulfonate, Igephon T type and aerosol type, and the like. And formalin condensates of naphthalene sulfonates, polystyrene sulfonates, polyvinyl sulfonates, polyaryl sulfonates, and salts of copolymers of acrylamide and acrylamidopropanesulfonic acid.
Examples of the copolymerizable polymer surfactant include a copolymer composed of a carboxylic acid monomer and a sulfonic acid monomer or a salt thereof.
Examples of the low-molecular phosphate ester salt include a higher alcohol monophosphate ester salt, a higher alcohol polyethylene oxide phosphate ester salt, and an alkylphenol polyethylene oxide phosphate ester salt.
[0011]
Among these anionic surfactants, in order to obtain a high-concentration slurry at the time of wet pulverization, a polymer type surfactant is preferable, but polyacrylic acid or a salt thereof, polyacrylic acid-maleic acid is particularly preferable. A carboxylic acid monomer such as a copolymer or a salt thereof alone or a copolymer of at least two or more of them or a salt thereof is exemplified. These molecular weights are not particularly limited, but are preferably 1,000 to 100,000, and more preferably 5,000 to 50,000.
Examples of the water-soluble surfactant (C) used as an organic dispersant include polyethylene glycol type and polyhydric alcohol type nonionic surfactants.
As the polyethylene glycol type, for example, higher alcohol ethylene oxide adduct, alkylphenol ethylene oxide adduct, fatty acid ethylene oxide adduct, polyhydric alcohol fatty acid ester ethylene oxide adduct, fatty acid amide ethylene oxide adduct, polypropylene glycol ethylene oxide adduct and And polyether modified silicone.
[0012]
Examples of the polyhydric alcohol type include glycerol fatty acid ester, pentaerythritol fatty acid ester, sorbitol and sorbitan fatty acid ester, sucrose fatty acid ester, polyhydric alcohol alkyl ether, polyglycerin fatty acid ester or ethylene oxide adduct thereof and Examples thereof include fatty acid amides of alkanolamines, and further include methylcellulose (MC), hydroxyethylcellulose (HEC), polyvinyl alcohol (PVA), polyalkylene oxide vinyl ether compound, and polyhydroxylalkyl (meth) acrylate. .
Among these nonionic surfactants, in order to obtain a high-concentration slurry at the time of wet pulverization, a polymer type surfactant is preferable, and particularly preferable are partially saponified popal and polyhydroxyalkyl ( (Meth) acrylate and the like.
Among the above various dispersants, a polyacrylic acid-based dispersant (for example, F-130 manufactured by San Nopco) is particularly preferable.
[0013]
In the present invention, in the above method, the concentration of the aqueous calcium carbonate slurry is adjusted to a predetermined concentration, and then the aqueous calcium carbonate aqueous slurry of the present invention is prepared by the following method using a centrifuge.
Method 1
The average particle diameter obtained by wet pulverization according to the above method is 0.5 to 2 μm, the solid content concentration is 74 to 80% by weight (preferably 75 to 77% by weight), and the viscosity at a liquid temperature of 20 ° C. is 300 mPas or less (more A heavy calcium carbonate aqueous slurry of preferably 200 mPas or less, particularly 50 to 150 mPas) is introduced into a centrifugal separator, and the centrifugal effect Z represented by the following formula is in the range of 200 to 3000 (preferably 500 to 1500). The difference between the solid concentration of the aqueous slurry before centrifugation and the solid concentration of the light liquid after centrifugation is 1% by weight or less (preferably 0.2 to 0.5% by weight) between the heavy liquid and the light liquid. The solid content concentration is 73 to 79% by weight (preferably 74 to 76% by weight), wherein a heavy liquid containing coarse particles is removed and a light liquid is collected. ) And the particle size 20μm greater than the content of heavy calcium carbonate 40ppm or less (preferably 20ppm or less) heavy process for the preparation of the calcium carbonate aqueous slurries is.
[Equation 2]
Z = (N2π2r) / (900g)
(Where N is the number of revolutions [rpm], r is the radius of gyration [m], g is the gravitational acceleration [m / sec]2]. )
[0014]
The average particle size obtained by wet pulverization by the above method is 0.5 to 2 μm, the solid content concentration is 30 to 70% by weight (preferably 40 to 60% by weight), and the viscosity at a liquid temperature of 20 ° C. is 100 mPas or less (preferably). Is introduced into the centrifugal separator a heavy calcium carbonate aqueous slurry of 50 mPas or less, particularly 10 to 40 mPas), and the centrifugal effect Z is in the range of 1000 to 3000 (preferably 1500 to 3000), and the heavy liquid and light liquid are continuously fed. A solid content concentration of 73 to 85% by weight (preferably 75 to 80% by weight), wherein the solid content concentration is centrifuged to remove the light liquid containing fine particles, and the heavy liquid is collected. , BET specific surface area is 6-12m2/ G aqueous calcium carbonate aqueous slurry.
[0015]
Method 3
The average particle diameter obtained by wet pulverization according to the above method is 0.5 to 2 μm, the solid content concentration is 74 to 80% by weight (preferably 75 to 77% by weight), and the viscosity at a liquid temperature of 20 ° C. is 300 mPas or less (more An aqueous slurry of heavy calcium carbonate (preferably 200 mPas or less, particularly 50 to 150 mPas) is introduced into a centrifugal separator, and the centrifugal effect Z is in the range of 200 to 3000 (preferably 500 to 1500). Then, centrifugal separation is continuously performed so that the difference between the solid content concentration of the aqueous slurry before centrifugation and the solid content concentration of the light liquid after centrifugation is 1% by weight or less to remove heavy liquid containing coarse particles. Then, the light liquid is recovered, and the obtained light liquid is diluted with water to have a solid content of 30 to 70% by weight (preferably 40 to 60% by weight) and a viscosity of 100 mPas or less (preferably 50 mPas). as below, especially 10 to 40 mPas), and the heavy calcium carbonate aqueous slurry is introduced into a centrifugal separator, and continuously centrifuged when the centrifugal effect Z is in the range of 1000 to 3000 (preferably 1500 to 3000). The liquid and the light liquid are centrifuged, the light liquid containing fine particles is removed, and the heavy liquid is collected. The solid content concentration is 73 to 85% by weight (preferably 75 to 80% by weight). Having a BET specific surface area of 6 to 12 m2/ G aqueous calcium carbonate aqueous slurry.
[0016]
The centrifugation operation can be performed by passing the solution through the centrifuge once or a plurality of times.
The centrifuge used in the present invention may be one generally used for solid-liquid separation or classification, and examples thereof include a decanter type and a basket type centrifuge. Among them, a decanter type centrifuge is preferable, and this centrifuge is used for wastewater treatment, kaolin classification, etc., and is used for separation and dehydration of large particles from fine particles having a specific gravity difference of about 2 to 5 μm or more. Although it is used, it is not suitable for separating ultrafine particles, and its allowable supply concentration is said to be 0.5 to 50% by weight. When a heavy calcium carbonate slurry with good dispersibility provided for coating is treated with a centrifuge, a hard cake is formed in the centrifuge and it is said that it is difficult to discharge the slurry. Has not been done. In the present invention, by supplying the heavy calcium carbonate slurry at a high concentration, the sedimentation speed in the centrifugal separator is controlled, and it is possible to discharge the slurry in a dilatant slurry state without forming a hard cake. The particle size distribution can be arbitrarily controlled by arbitrarily adjusting the centrifugal effect, the concentration of the supplied liquid, and the amount of the supplied liquid.
[0017]
【The invention's effect】
According to the present invention, there is provided an aqueous slurry of heavy calcium carbonate having a small content of coarse particles larger than 20 μm and a small content of fine particles of 0.2 μm or less. Further, according to the present invention, there is provided a method for efficiently preparing a heavy calcium carbonate aqueous slurry having such properties.
The heavy calcium carbonate aqueous slurry obtained by the present invention is suitably used for paper coating, but its use is not limited to paper coating, and it is dried as it is or by a conventional method, paint, abrasive, building material, And it can be used as a filler for plastics and rubbers.
Next, the present invention will be described with reference to examples.
[0018]
【Example】
Example 1
Water is added to heavy calcium carbonate having an average particle size of 8 μm (a dry-pulverized product of Japan Cement Limestone raw material), and anionic dispersant (polyacrylic acid-based dispersant, manufactured by San Nopco: F-130) per 100 parts by weight of heavy calcium carbonate ) Was added, and the mixture was wet-pulverized using a table-type medium stirring mill at a filling rate of glass beads having a diameter of 1.2 mm of 170% at a peripheral speed of 10 m / sec, and then classified through a 350 Mesh screen to classify heavy calcium carbonate. An aqueous slurry was prepared (average particle size 1.108 μm, particle size 20 μm or more and 100 ppm, particle size 0.2 μm or less 0.8%, solid content concentration 75.59% by weight, viscosity at 20 ° C. 130 mPas).
This aqueous slurry was placed in a decanter-type centrifuge (rotational radius 0.077 m, effective volume 1.8 liters) for 0.367 m.3/ G and a centrifugal force of 1500 G (centrifugal effect Z1500), coarse particles settled on the inner wall of the centrifuge. The sedimented coarse particles were transported to the outside by a screw and discharged. At this time, the concentration of the discharged slurry (heavy liquid) containing coarse particles was 83.28% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 1.399 μm.
[0019]
On the other hand, the concentration of the aqueous slurry (light liquid) discharged from the centrifugal separator was 75.39% by weight, and the average particle diameter of the heavy calcium carbonate contained therein was 1.084 μm, and the coarse particles larger than 20 μm Content was 0.8 ppm. In addition, an appropriate amount of water was showered on the aqueous slurry recovery side from the centrifugal separator to adjust the solid content concentration of the aqueous slurry and to prevent solidification.
The properties of the aqueous calcium carbonate aqueous slurry thus obtained are summarized in Table 1.
[0020]
Example 2
First, a heavy calcium carbonate aqueous slurry was prepared in the same manner as in Example 1 (average particle size: 1.341 μm, particle size: 20 μm to 455 ppm, particle size: 0.29 μm or less, 0.69%, solid content: 76. 22% by weight, viscosity at 20 ° C. 120 mPas).
0.825 m of the aqueous slurry was centrifuged in the same centrifuge as used in Example 1.3/ H, and a centrifugal force of 1500 G was applied (centrifugal effect Z1500), and coarse particles and an aqueous slurry were recovered in the same manner as in Example 1. The concentration of the slurry (heavy liquid) containing coarse particles was 86.0% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 2.018 μm.
On the other hand, the concentration of the aqueous slurry (light liquid) discharged from the centrifugal separator was 75.89% by weight, and the average particle diameter of the heavy calcium carbonate contained therein was 1.328 μm, which was larger than 20 μm. The content was 6 ppm.
[0021]
Example 3
First, a heavy calcium carbonate aqueous slurry was prepared in the same manner as in Example 1 (average particle size 1.284 μm, particle size 20 μm to 375 ppm, particle size 0.2 μm or less 0.82%, solid content 73. 93% by weight, viscosity at 20 ° C. 70 mPas).
This aqueous slurry was placed in the same centrifuge as used in Example 1 for 0.590 m.3/ H, and a centrifugal force of 600 G was applied (centrifugal effect Z600), and coarse particles and an aqueous slurry were recovered in the same manner as in Example 1. The concentration of the slurry (heavy liquid) containing coarse particles was 85.63% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 2.079 μm.
On the other hand, the concentration of the aqueous slurry (light liquid) discharged from the centrifugal separator was 73.53% by weight, and the average particle diameter of the heavy calcium carbonate contained therein was 1.284 μm, which was larger than 20 μm. The content was 12 ppm.
[0022]
Example 4
First, a heavy calcium carbonate aqueous slurry was prepared in the same manner as in Example 1 (average particle size: 1.104 μm, particle size: 20 μm to 105 ppm, particle size: 0.2 μm to 1.02%, solid content: 76. 95% by weight, viscosity at 20 ° C. 150 mPas).
This aqueous slurry was placed in the same centrifuge as used in Example 1 at 0.684 m.3/ H, and a centrifugal force of 2100 G was applied (centrifugal effect Z2100), and coarse particles and an aqueous slurry were recovered in the same manner as in Example 1. The concentration of the slurry (heavy liquid) containing coarse particles was 84.23% by weight, and the average particle size of heavy calcium carbonate contained therein was 1.392 μm.
[0023]
On the other hand, the concentration of the aqueous slurry (light liquid) discharged from the centrifugal separator was 74.91% by weight, and the average particle diameter of the heavy calcium carbonate contained therein was 1.096 μm, which was larger than 20 μm. The content was 3 ppm.
The aqueous slurry thus obtained was diluted with water to adjust the solid content concentration to 56% by weight, and the same type of centrifuge used in the previous step was used for 0.162 m.3/ H, and a centrifugal force of 1700 G was applied (centrifugal effect Z1700), and the heavy liquid and the light liquid were separated in the same manner as in Example 1. The concentration of the light liquid was 36.28% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 0.354 μm.
On the other hand, the concentration of heavy liquid discharged from the centrifugal separator is 78.42% by weight, and the average particle diameter of heavy calcium carbonate contained therein is 1.174 μm, and the content of fine particles smaller than 0.2 μm is It was 0%.
[0024]
Example 5
First, a heavy calcium carbonate aqueous slurry was prepared in the same manner as in Example 1 (average particle size: 1.100 μm, particle size: 20 μm to 95 ppm, particle size: 0.2 μm to 0.91%, solid content: 58. 0% by weight, viscosity at 20 ° C. 30 mPas).
This aqueous slurry was placed in the same centrifuge as used in Example 1 for 0.252 m.3/ H, and centrifugal force of 1400 G was applied (centrifugal effect Z1400), and coarse particles and an aqueous slurry were recovered in the same manner as in Example 1. The concentration of the slurry containing coarse particles was 80.35% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 1.342 μm.
On the other hand, the concentration of the aqueous slurry discharged from the centrifugal separator was 57.0% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 0.762 μm, and the content of coarse particles larger than 20 μm was 0%. 0.1 ppm.
The aqueous slurry thus obtained was placed in a centrifuge of the same type as used in the previous step for 0.162 m.3/ H, and a centrifugal force of 2100 G was applied (centrifugal effect Z2100) to separate heavy and light liquids in the same manner as in Example 1. The concentration of the light liquid was 40.26% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 0.365 μm.
[0025]
On the other hand, the concentration of the heavy liquid discharged from the centrifuge is 78.29% by weight, and the average particle diameter of heavy calcium carbonate contained therein is 0.879 μm, and the content of fine particles smaller than 0.2 μm is 0.67%.
Example 6
First, a heavy calcium carbonate aqueous slurry was prepared in the same manner as in Example 1 (mean particle size: 1.100 μm, particle size: 20 μm to 95 ppm, particle size: 0.2 μm to 0.91%, solid content: 60. 3% by weight, viscosity at 20 ° C. 45 mPas).
0.162 m of the aqueous slurry was centrifuged in the same centrifuge as used in Example 1.3/ H, and a centrifugal force of 1700 G was applied (centrifugal effect Z1700), and light and heavy liquids were collected in the same manner as in Example 1. The concentration of the light liquid was 49.12% by weight, and the average particle diameter of heavy calcium carbonate contained therein was 0.512 μm.
On the other hand, the concentration of heavy liquid discharged from the centrifuge is 77.58% by weight, and the average particle diameter of heavy calcium carbonate contained therein is 1.249 μm, and the content of fine particles smaller than 0.2 μm is It was 0%.
The properties described in Examples 1 to 6 and the properties of the obtained slurries and commercial products A and B were measured by the following methods.
[0026]
viscosity
After adjusting the temperature of the aqueous slurry to 20 ° C., the measurement was performed using a Tokyo Keiki B-type viscometer,
Solids concentration
The absolute dry weight at 105 ± 5 ° C. was determined, and the solid content concentration was calculated.
BET specific surface area measurement method
BET specific surface area measuring device: manufactured by Yuasa Ionics Co., Ltd .: measured with a monosoap type.Particle size distribution
Laser diffraction particle size distribution analyzer: Nikkiso Co., Ltd .: Measured with Microtrac X-100. The particle size of 50% by weight of the obtained particle size distribution measurement curve is defined as the average particle size, and the ratio of the particle size of 50% by weight of the particle size distribution measurement curve to the particle size of 10% by weight of the particle size distribution measurement curve is D.50/ D10Asked. In addition, this ratio approaches 1 as the width of the particle size distribution becomes narrower.
Table 1 shows the characteristics of the slurries obtained in Examples 1 to 3, and Table 2 shows the characteristics of the slurries obtained in Examples 4 to 6 and the commercial products A and B.
[0027]
[Table 1]
Table-1
[Table 2]
Table-2
The heavy calcium carbonate slurry of the present invention whose particle size distribution is controlled in Table 2 is D50/ D10It can be seen that the BET specific surface area is smaller than that of the conventional product and fine particles are removed. For example, the commercially available product B is provided for the purpose of improving the gloss, but has a larger specific surface area than the generally used commercially available product A, which increases the necessary amount of the binder and the like, and adversely affects the optical characteristics of the coated paper. However, in Example 5 of the present invention, the BET specific surface area was small, the required amount of the binder was small, and the optical properties of the coated paper were favorably affected, despite the small average particle size compared to the commercial product A. Can be. In addition, the whiteness of the commercial product decreases as the particles are reduced, but the whiteness of the product of the present invention is improved because fine particles having a particle size of 0.2 μm or less are removed.
[Brief description of the drawings]
FIG. 1 shows a particle size distribution curve of a commercial product A.
FIG. 2 shows a particle size distribution curve of a commercial product B.
FIG. 3 shows a particle size distribution curve of the aqueous solution of heavy calcium carbonate obtained in Example 4.
FIG. 4 shows a particle size distribution curve of the aqueous calcium carbonate slurry obtained in Example 5.
Claims (4)
Ｚ＝（Ｎ２ π２ ｒ）／（９００ｇ）
（式中、Ｎは回転数［ｒｐｍ］ 、ｒは転半径［ｍ］ 、ｇは重力加速度［ｍ／ｓｅｃ２ ］ を表す。）A heavy calcium carbonate aqueous slurry having an average particle size of 0.5 to 2 μm, a solid concentration of 74 to 80% by weight, and a viscosity at a liquid temperature of 20 ° C. of 300 mPas or less is continuously fed to a centrifuge. The centrifugal effect Z represented by the following formula is within the range of 200 to 3000, and the heavy liquid and the light liquid are divided into the solid content concentration of the aqueous slurry before centrifugation and the light liquid after centrifugation. Characterized by continuously centrifuging and collecting the light liquid so that the difference in solids concentration is 1% by weight or less, wherein the solids concentration is 73 to 79% by weight and the particle size is from 20 μm. A method for preparing an aqueous slurry of heavy calcium carbonate having a content of large heavy calcium carbonate of 40 ppm or less.
Z = (N 2 π 2 r) / (900 g)
(In the formula, N represents the number of revolutions [rpm], r represents the turning radius [m], and g represents the gravitational acceleration [m / sec 2 ].)
Ｚ＝（Ｎ２ π２ ｒ）／（９００ｇ）
（式中、Ｎは回転数［ｒｐｍ］ 、ｒは転半径［ｍ］ 、ｇは重力加速度［ｍ／ｓｅｃ２ ］ を表す。）An aqueous slurry of heavy calcium carbonate having an average particle diameter of 0.5 to 2 μm, a solid content of 30 to 70% by weight, and a viscosity at a liquid temperature of 20 ° C. of 100 mPas or less is continuously introduced into a centrifuge. The centrifugal effect Z is in the range of 1,000 to 3,000, and continuously centrifuged into a heavy liquid and a light liquid, and the heavy liquid is collected. A method for preparing an aqueous slurry of heavy calcium carbonate having a BET specific surface area of 6 to 12 m 2 / g.
Z = (N 2 π 2 r) / (900 g)
(In the formula, N represents the number of revolutions [rpm], r represents the turning radius [m], and g represents the gravitational acceleration [m / sec 2 ].)
Ｚ＝（Ｎ２ π２ ｒ）／（９００ｇ）
（式中、Ｎは回転数［ｒｐｍ］ 、ｒは転半径［ｍ］ 、ｇは重力加速度［ｍ／ｓｅｃ２ ］ を表す。）A heavy calcium carbonate aqueous slurry having an average particle size of 0.5 to 2 μm, a solid concentration of 74 to 80% by weight, and a viscosity at a liquid temperature of 20 ° C. of 300 mPas or less is continuously fed to a centrifuge. The centrifugal effect Z represented by the following formula is within the range of 200 to 3000, and the heavy liquid and the light liquid are divided into the solid content concentration of the aqueous slurry before centrifugation and the light liquid after centrifugation. The light liquid is recovered by centrifuging continuously so that the difference in the solid concentration of the liquid becomes 1% by weight or less, water is added to the light liquid to obtain a solid concentration of 30 to 70% by weight, and the liquid temperature is 20 ° C. Is adjusted to 100 mPas or less, the heavy calcium carbonate aqueous slurry is continuously introduced into a centrifuge, and the centrifugal effect Z is in the range of 1,000 to 3,000, and continuously into heavy liquid and light liquid, Centrifuging and collecting heavy liquid A process for preparing heavy calcium carbonate aqueous slurries of claim 1, wherein.
Z = (N 2 π 2 r) / (900 g)
(In the formula, N represents the number of revolutions [rpm], r represents the turning radius [m], and g represents the gravitational acceleration [m / sec 2 ].)
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| JP5028565B2 (en) * | 2004-12-16 | 2012-09-19 | サンノプコ株式会社 | Method for producing heavy calcium carbonate slurry |
| JP2006327914A (en) * | 2005-05-30 | 2006-12-07 | Nippon Paper Industries Co Ltd | Manufacturing method of calcium carbonate and coated paper using the same |
| JP4688657B2 (en) * | 2005-12-06 | 2011-05-25 | 太平洋セメント株式会社 | Cement admixture and method for producing the same |
| JP5114729B2 (en) * | 2005-12-15 | 2013-01-09 | 王子ホールディングス株式会社 | Calcium carbonate particles and news paper for cold offset printing |
| PL2302131T3 (en) * | 2009-09-21 | 2012-09-28 | Omya Int Ag | Aqueous slurries comprising fine calcium carbonate particles for their use in paper coatings |
| JP5415202B2 (en) * | 2009-09-29 | 2014-02-12 | 太平洋セメント株式会社 | Method for producing heavy calcium carbonate |
| SI2390284T1 (en) * | 2010-05-28 | 2012-07-31 | Omya Development Ag | Process for manufacturing high solids suspensions of mineral materials |
| JP2013112560A (en) * | 2011-11-28 | 2013-06-10 | Jdc Corp | Layered double hydroxide particle group, method for producing the same, layered double hydroxide dispersion, and layered double hydroxide-added resin |
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1998
- 1998-07-14 JP JP19844498A patent/JP3595686B2/en not_active Expired - Lifetime
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