JP2004107513A - Oxidation-treated carbon black, production method and water dispersion thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxidation-treated carbon black suitable for water-based ink or the like for an inkjet printer; and to provide a production method and a water dispersion thereof. <P>SOLUTION: The oxidation-treated carbon black is obtained by subjecting a carbon black satisfying the relations of CTAB×Vp<170 and 1<Vp<CTAB<10 (wherein, CTAB (cetyl trimethyl ammonium bromide) is a value of a CTAB specific surface area; and Vp is a space volume of aggregate) to oxidation treatment with a peroxo diacid or a salt thereof so as to have 2-5 μmol/m<SP>2</SP>carboxy group, and neutralizing at least a part of the carboxy group with an alkali having <5 dissociation constant. The method for producing the oxidation-treated carbon black involves removing remaining salt after the neutralization. The water dispersion of the oxidation-treated carbon black is obtained by dispersing the oxidation-treated carbon black in the water and subjecting the dispersion to classification treatment so that the average particle diameter Dupa50% of agglomerate in the dispersion is 50-130 nm, the maximum particle diameter Dupa99% is 150-320 nm, and the ratio ΔDupa (mode)/Dupa (mode) of the half width [ΔDupa (mode)] of the agglomerate to the mode particle diameter [Dupa (mode)] is ≤1.20. <P>COPYRIGHT: (C)2004,JPO

Description

但し、Ｖｐ；　凝集体空隙容積（ｃｍ^３／ｇ）
Ｘ１　；　圧力２５ｐｓｉでの静電容量（ｐＦ）
Ｘ２　；　圧力３００００ｐｓｉでの静電容量（ｐＦ）
Ｗ　　；　カーボンブラック試料に重量（ｇ）
ＣＦ；　セルにより決まる定数
【００２６】
本発明の酸化処理カーボンブラックは、ＣＴＡＢ比表面積及び凝集体空隙容積Ｖｐが上記の関係を充足するカーボンブラックを対象として、ペルオキソ２酸あるいはペルオキソ２酸塩により、カーボンブラック粒子表面のカルボキシル基量が２〜５μｍｏｌ／ｍ^２に酸化処理される。
【００２７】
本発明において、カーボンブラックを酸化処理するための酸化剤にはペルオキソ２酸やペルオキソ２酸塩が限定的に用いられる。ペルオキソ２酸としては、例えばペルオキソ硫酸、ペルオキソ炭酸、ペルオキソ燐酸などが、また塩にはアルカリ金属塩やアンモニウム塩などが例示される。
【００２８】
酸化剤をこのように限定する理由は、他の酸化剤、例えば次亜ハロゲン酸やその塩を使用した場合には、カーボンブラック中にハロゲンが残存し、このカーボンブラックを顔料に用いた印字物を焼却処分する際にダイオキシンなどが発生する懸念があり、環境上問題となるからである。また、重クロム酸やその塩、過マンガン酸やその塩なども酸化後のカーボンブラック中あるいは廃液中に重金属が残留し易く、環境汚染の問題が生じる可能性があるからである。
【００２９】
硝酸による酸化はカーボンブラック表面にニトロソ基が形成され、このニトロソ基を有するカーボンブラックは変異原生を有し、人体に有害である。また、過酸化水素による酸化では酸化力が弱く、水分散性に有効機能するカルボキシル基を十分に生成させることが難しい。
【００３０】
更に、オゾンによる気相酸化ではチャネリング現象が起こるためにカーボンブラック表面に均一にカルボキシル基を生成させることができず、酸化力も弱いのでカルボキシル基の生成量も少ない。なお、液相中でオゾンをバブリングさせて酸化する方法ではオゾンの水への溶解度が低いため、カルボキシル基の生成量がより少なくなる。
【００３１】
一般に、カーボンブラックを酸化処理すると、酸化条件によってカルボキシル基（−ＣＯＯＨ）、ヒドロキシル基（−ＯＨ）、キノン基（＞Ｃ＝Ｏ）などの種々の官能基が生成する。これらの官能基のうち水分子との親和性が高く、水中で安定な分散状態を形成するためには活性水素を含む酸性官能基であるカルボキシル基及びヒドロキシル基の存在量が大きく関係する。しかし、ヒドロキシル基の解離常数は８〜１０で、カルボキシル基の２〜５に比べて非常に大きいので、水分散性に関与する官能基はカルボキシル基が支配的となる。また、キノン基は水分子との親和性が小さく、むしろ水中への分散性を阻害する要因となる。
【００３２】
したがって、カーボンブラック粒子表面に存在する官能基としてカルボキシル基量を増加させれば水への分散性は向上することになる。一方、水への親和性が向上するとカーボンブラックの紙繊維間への浸透性も大きくなり、印字した際に黒色度が低下する傾向が生じる。また、カーボンブラックが水中に分散する過程及び水中に分散した状態においては、カーボンブラックと水分子との接触界面に存在する親水性の官能基量が重要な機能を発揮する。したがって、カーボンブラック単位重量当たりの官能基量では分散性能の良否を的確に評価することができない。そこで、水分散性と黒色度とを両立させるという観点から、カルボキシル基量を２〜５μｍｏｌ／ｍ^２に設定する。
【００３３】
本発明の酸化処理カーボンブラックは、このように液相酸化して生成したカルボキシル基の少なくとも一部が解離定数（ｐＫａ）　が５未満のアルカリ溶液で中和されたものである。解離定数が５以上のアルカリ溶液（例えば炭酸水素ナトリウムや酢酸ナトリウムなど）で中和すると、僅かではあるが生成したヒドロキシル基をフェノラート塩に置換することが困難となり、分散体中のカーボンブラックの分散安定性が経時的に不安定になる可能性が高くなるためである。
【００３４】
解離定数（ｐＫａ）　が５未満のアルカリ溶液には、例えば無機系としては水酸化リチウム、水酸化ナトリウム、水酸化カリウムなどが、有機系としては水酸化テトラメチルアンモニウム、水酸化テトラエチルアンモニウムなどが例示される。
【００３５】
本発明の酸化処理カーボンブラックの製造方法は、ＣＴＡＢ比表面積（１０^３ｍ^２／ｋｇ）と凝集体空隙容積Ｖｐ（１０^−３ｍ^３／ｋｇ）とが、（１）、（２）ＣＴＡＢ×Ｖｐ＜１７０（ｍ^５／ｋｇ^２）…（１）
１（ｎｍ）＜Ｖｐ／ＣＴＡＢ＜１０（ｎｍ）…（２）
の関係を充足するカーボンブラックをペルオキソ２酸あるいはペルオキソ２酸塩の水溶液中に入れ、酸化剤濃度、カーボンブラックの添加量、反応温度、反応時間、攪拌速度などを適宜に制御して混合攪拌することにより、カルボキシル基量を２〜５μｍｏｌ／ｍ^２に酸化処理した後、解離定数（ｐＫａ）　が５未満のアルカリ溶液を加えて生成したカルボキシル基の少なくとも一部を中和し、次いで残塩を除去することを特徴とする。
【００３６】
アルカリ溶液で中和した酸化カーボンブラックの分散液には、中和により生成した塩類が存在するので、これらの残塩は電気透析あるいは逆浸透膜、限外濾過膜、ルーズＲ．Ｏなどの分離膜で分離除去して、酸化カーボンブラックが精製される。残塩除去が不十分な場合には、水分散体の分散性、保存安定性、粘性などが悪化し、また装置腐食の問題も生じることになるので、カーボンブラック水分散体の残塩濃度は、カーボンブラックの分散濃度を２０ｗｔ％として電気伝導度が２ｍＳ／ｃｍ　未満となるように除去することが好ましい。
【００３７】
なお、カルボキシル基量は下記の方法によって測定される。
（３）カルボキシル基；
濃度０．９７６ｍｏｌ／ｄｍ^３　の炭酸水素ナトリウム０．５ｄｍ^３の中にカーボンブラック２〜５ｇ　を添加して６時間振盪した後、カーボンブラックを反応液から濾別し、濾液に濃度０．０５ｍｏｌ／ｄｍ^３　の塩酸水溶液を加えた後、ｐＨが７．０になるまで濃度０．０５ｍｏｌ／ｄｍ^３　の水酸化ナトリウム水溶液にて中和滴定試験を行ってカルボキシル基を定量する。次に、この測定値をカーボンブラックの窒素吸着比表面積（Ｎ_２ＳＡ　；ｍ^２／ｇ）で除した値をカルボキシル基量（μｍｏｌ／ｍ^２）とする。
【００３８】
本発明の酸化処理カーボンブラックの水分散体は、上記の酸化処理カーボンブラックを水中に分散させ、更に分級処理を行って、カーボンブラックの粒子凝集形態を特定した点を特徴とする。カーボンブラックを水中に分散させる場合、水中への分散が容易で、その分散状態を安定に維持するためにはカーボンブラック粒子がより微細な凝集形態で水中に分散し、かつ再凝集して大きな凝集体を形成し難いことが有利である。一方、カーボンブラック粒子の凝集形態が小さくなると分散性能の向上には有利ではあるが、水性インキとした場合には紙繊維の間隙からカーボンブラックが通過し易くなり、紙定着濃度が低下して黒色度が低くなる。しかし、凝集形態が大きくなると分散性が低下し、インキの吐出安定性や濾過性の悪化を招くことになる。
【００３９】
更に、原料のカーボンブラックの粒子凝集体には粒度分布があり、酸化処理したカーボンブラックにおいても当然粒度分布があり、例えば小さな粒子凝集体では酸化が不十分なために水分散性が低いものも存在するうえ、一方では沈降し易い大きな凝集体も含まれている。そのため、酸化が不十分なもの及び粒度の大きなものを選択的に除去することが必要となる。選択除去する手段としては分級処理があり、遠心分離による方法、機能性膜による分離などが施される。
【００４０】
すなわち、本発明の酸化処理カーボンブラックの水分散体は分級処理により水分散体中のカーボンブラックの粒子凝集体、すなわちアグロメレート粒径の粒度分布のシャープ化を図るもので、具体的には水分散体中においてカーボンブラックのアグロメレートの平均粒径Ｄｕｐａ５０％が５０〜１３０ｎｍ、最大粒径Ｄｕｐａ９９％が１５０〜３２０ｎｍ、アグロメレートの半値幅ΔＤｕｐａ（ｍｏｄｅ）　とモード粒径Ｄｕｐａ（ｍｏｄｅ）　との比ΔＤｕｐａ（ｍｏｄｅ）　／Ｄｕｐａ（ｍｏｄｅ）　が１．２０以下に分級処理されたことを特徴とする。なお、カーボンブラックの分散濃度は５０ｗｔ％以下に調整することが好ましい。分散濃度が５０ｗｔ％を越えると分散体中においてカーボンブラックが再凝集し易くなり、長期間に亘って安定分散を維持することが難しくなる傾向があるからである。
【００４１】
アグロメレートの平均粒径Ｄｕｐａ５０％の値が５０ｎｍ未満であると、例えば水性インキを調製し、紙に印字した場合に、紙繊維の隙間からカーボンブラックが通過する割合が多くなり紙定着濃度すなわち黒色度が低下する。一方、１３０ｎｍを越えると紙繊維表面に捕捉されるカーボンブラック量が増えるので黒色度は向上するが、分散安定性が低下して、濾過性やインクノズルからの吐出安定性が低下し、沈殿残渣率が増大するなどの問題を招くことになる。また、アグロメレートの最大粒径Ｄｕｐａ９９％の値が１５０ｎｍ未満では黒色度が低下し、３２０ｎｍを越えると濾過性、吐出安定性の低下及び沈殿残渣率の増大が著しくなる。更に、アグロメレートの半値幅ΔＤｕｐａ（ｍｏｄｅ）　とモード粒径Ｄｕｐａ（ｍｏｄｅ）　の比ΔＤｕｐａ　（ｍｏｄｅ）／Ｄｕｐａ（ｍｏｄｅ）　の値を１．２０以下に分級処理にて調整することにより、濾過性、吐出安定性が向上し、沈殿残渣率の低下を図ることができる。
【００４２】
なお、Ｄｕｐａ５０％、Ｄｕｐａ９９％、Ｄｕｐａ（ｍｏｄｅ）　、ΔＤｕｐａ（ｍｏｄｅ）　は下記の方法によって測定される。
（４）Ｄｕｐａ５０％、Ｄｕｐａ９９％、Ｄｕｐａ（ｍｏｄｅ）　、ΔＤｕｐａ（ｍｏｄｅ）　の測定；
カーボンブラックを水に分散して０．１〜０．５ｋｇ／ｍ^３　の分散液を調製し、ヘテロダインレーザードップラー方式粒度分布測定装置（マイクロトラック社製、ＵＰＡ　ｍｏｄｅ１　９３４０）を用いて分散液にレーザー光を照射して、散乱光の周波数変調の度合いから分散液中のアグロメレートの粒径を測定する。分散液中のカーボンブラックはブラウン運動しており、ドップラー効果によって分散しているカーボンブラック凝集体の大きさにより散乱光の周波数が変調する。したがって、凝集体の大きさによってブラウン運動の激しさが異なることから、水中に分散している状態における凝集体の大きさ、すなわちアグロメレートの粒径を測定することができる。
【００４３】
このようにして測定したアグロメレート粒径から、その累積度数分布曲線を作成し、５０％累積度数の値をアグロメレートの平均粒径Ｄｕｐａ５０％（ｎｍ）、９９％累積度数の値をアグロメレートの最大粒径Ｄｕｐａ９９％（ｎｍ）とする。また、測定したアグロメレート粒径から、その頻度数分布曲線を作成し、この頻度数分布曲線からモード径Ｄｕｐａ（ｍｏｄｅ）　（ｎｍ）を求め、更にモード径における頻度値の１／２に相当する大小２点間の粒子径差を求めて、半値幅ΔＤｕｐａ（ｍｏｄｅ）　（ｎｍ）とする。
【００４４】
なお、本発明の酸化処理カーボンブラックの水分散体を水性黒色インキなどとして使用する場合には、例えばカーボンブラック分散濃度を２０ｗｔ％に調整したときの電気伝導度を２ｍＳ／ｃｍ未満とすることが好ましい。分級処理したカーボンブラック水分散体には未中和塩などが存在し、これらの塩が多量に存在すると塩析によりカーボンブラックが凝集沈殿を起こすので、速やかに脱塩精製することが好ましい。脱塩精製の方法としては、限外濾過膜、逆浸透膜、電気透析などの機能性膜により精製濾過を行い、長期間安定な分散状態を維持し得るように、電気伝導度を２ｍＳ／ｃｍ未満に調整される。この水分散体における電気伝導度が２ｍＳ／ｃｍ以上であると、長期間保存中にカーボンブラックから溶出してくるフミン酸塩などの塩の影響によりカーボンブラックの凝集が起こり、粘度の増大や分散安定性が低下する場合がある。また、インキ媒体になった場合には装置、機械などを腐食するという問題を生じることもある。
【００４５】
更に、インクジェット用の記録液用インキなどとして用いる場合には、例えばカーボンブラックの分散濃度を２０ｗｔ％として、２５℃での粘度１０ｍＰａ・ｓ以下、比重１．３以下、表面張力６０ｍＮ／ｍ以上、ｐＨ４〜９、沈殿残渣率　４０ｗｔ％未満などの性状に調整して使用される。
【００４６】
すなわち、粘度が１０ｍＰａ・ｓを越えるとプリンタヘッドに詰まりを生じ易くインキの吐出安定性が低下し、比重が１．３０を越えるとチキソトロピー化を起こす可能性が高い。表面張力が６０ｍＮ／ｍ未満ではノズル先端の濡れなどにより印字汚れが発生して印字品位が損なわれることになり、ｐＨが４未満では粘度が上昇して分散安定性も悪化し、ｐＨが９を越えると印字したときに耐水性が低下し、また加温による粘度上昇を招くことになる。また、水分散体の沈殿残渣率が４０ｗｔ％を越えると分散安定性が著しく低下することとなるためである。なお、本発明による水分散体におけるカーボンブラック含有量を４ｗｔ％として純水で希釈し、＃６バーコータによりコピー紙（ゼロックス４０２４紙）にドローダウンした場合の黒色度（光濃度）１．４０以上と十分な印字濃度が得られる。
【００４７】
このように、本発明の酸化処理カーボンブラックを水中に分散させた水分散体は、分散性能の経時安定性に優れており、また、耐水性や耐光性も良好であるので、水性黒色インキなどとして好適に使用することができる。
【００４８】
以下、本発明の実施例を比較例と対比して具体的に説明する。
【００４９】
実施例１〜２、比較例１〜２
表１に示すＣＴＡＢ比表面積及び凝集体空隙容積Ｖｐの異なるカーボンブラック１００ｇを、濃度１．０ｍｏｌ／ｄｍ^３のペルオキソ２硫酸ナトリウム水溶液３ｄｍ^３に添加し、反応温度３３３ｋ、攪拌速度０．１２　ｓ^−１の条件で１０時間攪拌混合して酸化処理した。次いで、濾別した酸化処理カーボンブラックを純水中に分散させて、濃度１．０ｍｏｌ／ｄｍ^３の水酸化ナトリウム水溶液で中和した。中和後、遠心分離器（日立工機社製　ＣＲ２２Ｆ）で７．５×１０^−３ｓ　^−１の回転数で１５分間分級処理した。その後、上澄み液を限外濾過膜〔旭化成社製、ＡＨＰ−１０１０、分画分子量　５００００）により残存する塩を分離したのち、カーボンブラック分散濃度が２０ｗｔ％になるように水を除去した。この酸化処理カーボンブラック水分散体の電気伝導度は１．３ｍＳ／ｃｍであった。
【００５０】
比較例３
実施例１と同じカーボンブラック１００ｇを濃度１．０ｍｏｌ／ｄｍ^３の過マンガン酸カリウム水溶液３ｄｍ^３に添加し、反応温度３４３ｋ、攪拌速度０．１２　ｓ^−１の条件で３時間攪拌混合して酸化処理した他は、実施例１と同じ方法で中和処理、分級処理、残塩分離処理を行ったのち、水を除去して分散濃度２０ｗｔ％の酸化処理カーボンブラックの水分散体を製造した。なお、この水分散体の電気伝導度は１．５ｍＳ／ｃｍであった。
【００５１】
比較例４
実施例１と同じカーボンブラック１００ｇを有効塩素濃度４％の次亜塩素酸ナトリウム水溶液３ｄｍ^３に添加し、反応温度３７３ｋ、攪拌速度０．１２　ｓ^−１の条件で５時間攪拌混合して酸化処理した後、塩酸でｐＨ２に調整した他は、実施例１と同じ方法で中和処理、分級処理、残塩分離処理を行ったのち、水を除去して分散濃度２０ｗｔ％の酸化処理カーボンブラックの水分散体を製造した。なお、この水分散体の電気伝導度は１．２ｍＳ／ｃｍであった。
【００５２】
比較例５
実施例１と同じカーボンブラック１００ｇをオゾン処理器に入れ、オゾン発生機（日本オゾン社製、ＩＯＴ−４Ａ６　）により発生電圧２００Ｖ、オゾン発生量１８ｇ／ｈの条件で１時間酸化処理した他は全て実施例１と同じ方法で中和処理、分級処理、残塩分離処理を行ったのち、水を除去して分散濃度２０ｗｔ％の酸化処理カーボンブラックの水分散体を製造した。なおこの水分散体の電気伝導度は０．８ｍＳ／ｃｍであった。
【００５３】
比較例６
ペルオキソ２硫酸ナトリウム水溶液の濃度を２．０ｍｏｌ／ｄｍ^３にした他は全て実施例１と同じ方法で酸化処理、中和処理、分級処理、残塩分離処理を行って後、水を除去して分散濃度２０ｗｔ％の酸化処理カーボンブラックの水分散体を製造した。なお、この水分散体の電気伝導度は０．８ｍＳ／ｃｍであった。
【００５４】
比較例７
酸化処理後の中和処理を、濃度１．０ｍｏｌ／ｄｍ^３の炭酸水素トリウム水溶液で中和した他は全て実施例１と同じ方法で酸化処理、分級処理、残塩処理を行って後、水を除去して分散濃度２０ｗｔ％の酸化処理カーボンブラックの水分散体を製造した。なお、この水分散体の電気伝導度は１．２ｍＳ／ｃｍであった。
【００５５】
比較例８
分級処理を行わない他は全て実施例１と同じ方法で酸化処理、中和処理、分級処理、残塩分離処理を行って後、水を除去して分散濃度２０ｗｔ％の酸化処理カーボンブラックの水分散体を製造した。なお、この水分散体の電気伝導度は１．２ｍＳ／ｃｍであった。
【００５６】
このようにして製造した酸化処理カーボンブラックの水分散体について、製造条件を対比して表１、２に示した。
【００５７】
【表１】

表注；
＊１　Ａ；Ｎａ_２Ｓ_２Ｏ_８
Ｂ；ＫＭｎＯ_４
【００５８】
【表２】

表注；
＊１　Ａ；Ｎａ_２Ｓ_２Ｏ_８
Ｃ；ＮａＣｌＯ
Ｄ；Ｏ_３
＊２　有効塩素濃度　４％
【００５９】
次に、これらのカーボンブラックの水分散体中のカーボンブラックアグロメレートの平均粒径Ｄｕｐａ５０％（ｎｍ）、最大粒径Ｄｕｐａ９９％（ｎｍ）、モード粒径Ｄｕｐａ（ｍｏｄｅ）　（ｎｍ）及び半値幅ΔＤｕｐａ（ｍｏｄｅ）（ｎｍ）　を測定した。また下記の方法により測定して、水分散性能およびインキ性能などを評価した。得られた結果を表３、４に示した。
【００６０】
保存安定性；
サンプルを密閉容器に入れ、７０℃の温度に保持して１〜４週間各経過後の粘度を測定して保存安定性を比較した。なお、粘度は回転振動式粘度計〔山一電機（株）製、ＶＭ−１００Ａ−Ｌ　〕により測定した。
【００６１】
アグロメレートの粒子径；
サンプルを密閉容器に入れ、７０℃の温度に保持して１〜４週間経過後のアグロメレートの粒子径を測定して、その変化を比較した。
【００６２】
濾過性；
サンプルを濾紙（アドバンテックＴＯＹＯ製Ｎｏ．２）及び膜孔径３μｍ　、０．８μｍ　、０．６５μｍ　、０．４５μｍ　のフィルターを用いて２．６６×１０^３Ｐａ　の減圧下で濾過試験を行い、通過量を測定した。
【００６３】
沈殿残渣率；
サンプルを２００００Ｇの重力加速度で３０分間遠心分離処理を行った後の沈殿残渣量（Ｍ　１）と、遠心分離処理前のカーボンブラックの重量（Ｍ　０）との重量比（Ｍ　１／Ｍ　０）を沈殿残渣率とした。
【００６４】
印字濃度；
カーボンブラック水分散体をカーボンブラック分散濃度４ｗｔ％に希釈し、コピー紙（ＸＥＲＯＸ　４０２４）に＃６バーコーダにより印字して、マクベス濃度計（コルモーゲン社製　ＲＤ−９２７　）を用いて光学濃度を測定した。
【００６５】
【表３】

【００６６】
【表４】

【００６７】
表１〜４の結果から、実施例１、２の水分散体は優れた保存安定性、濾過性、沈殿残渣率、印字濃度等をバランス良く備えているが、カーボンブラックのＶｐ／ＣＴＡＢが大きい比較例１は沈殿残渣率が著しく多く、カーボンブラックのＣＴＡＢ×Ｖｐ値が大きい比較例２では初期粘度が高くなっている。
【００６８】
酸化剤に過マンガン酸カリウムを使用した比較例３は残留重金属が多く、また酸化剤に次亜塩素酸ナトリウムを用いた比較例４は残留ハロゲンが多く、ともに環境汚染、公害上問題となり、好ましくない。
【００６９】
また、酸化剤にオゾンを用いた比較例５では、オゾンの酸化力が弱いのでカーボンブラックが十分に酸化されないため分散性能及び濾過性の低下が著しく、一方、比較例６のように酸化により生成したカルボキシル基量が多くなると、水分散性能は優れているが、印字濃度が低位になる。
【００７０】
炭酸水素ナトリウムにより中和した比較例７は水分散性能が低下し、分級処理を行わない比較例８の水分散体では濾過性の低下が大きくなる。
【００７１】
【発明の効果】
以上のとおり、本発明によれば、水分散性能に優れた酸化処理カーボンブラックとその製造方法が提供され、また、この酸化処理カーボンブラックを水中に分散させた本発明の水分散体によれば、濾過性、沈殿残渣率など分散性の長期安定性が良好であり、印字濃度も濃く、インクジェットプリンター用をはじめとして水性インキとして優れた実用性が期待される。[0001]
TECHNICAL FIELD OF THE INVENTION
INDUSTRIAL APPLICABILITY The present invention has excellent dispersibility in water and is suitable for use as an oxidized carbon black as a black pigment for aqueous inks, a method for producing the oxidized carbon black, and an aqueous dispersion useful as an aqueous black ink obtained by dispersing the oxidized carbon black in water. About the body.
[0002]
[Prior art]
Since carbon black is hydrophobic and has low wettability with water, it is extremely difficult to stably disperse carbon black at a high concentration in water. This is because the number of functional groups having high affinity for water molecules existing on the carbon black surface is extremely small. Therefore, when using as a black pigment in an aqueous ink or the like in which carbon black is dispersed in water, it is necessary to improve the water dispersion performance by modifying the properties of the surface of the carbon black particles. Therefore, a method of forming a hydrophilic functional group on the surface by oxidatively modifying carbon black has long been known.
[0003]
For example, Patent Document 1 discloses a method of oxidizing carbon black with an aqueous solution of hypohalite, and Patent Document 2 discloses a method of producing a water-dispersible modified carbon black in which carbon black is subjected to low-temperature oxidative plasma treatment. It has been disclosed. However, it is difficult to oxidize a large amount of carbon black uniformly by the oxidation treatment using low-temperature plasma.
[0004]
Carbon black having excellent water dispersibility has been useful as a pigment for aqueous black ink, and has attracted attention as a recording liquid for ink jet printers, especially in writing instruments in recent years. As a water-based ink using a water-dispersible carbon black, a method for producing a water-based ink for improving dispersibility in water by using a coupling agent or a surfactant to carbon black subjected to light oxidation treatment (Patent Document 3, Patent Document 4, Patent Document 5, Patent Document 6, etc.) are also known, but they must be stable for a long period of time due to deterioration due to oxidation or decomposition of coupling agents and surfactants due to temperature changes or changes over time. It is difficult.
[0005]
As an aqueous ink using a water-dispersible carbon black, for example, Patent Document 7 discloses an aqueous pigment ink containing water and carbon black, wherein the carbon black has a surface active hydrogen content of 1.5 mmol / g or more. In the method for producing an aqueous pigment ink having water and an aqueous pigment ink containing water and carbon black, (a) a step of obtaining an acidic carbon black, and (b) a step of converting the acidic carbon black with a hypohalite in water. Further, there has been proposed a method for producing an aqueous pigment ink including a step of oxidizing. Patent Document 8 discloses that the absorption amount is 100 cm.³A method for producing an aqueous pigment ink, comprising: a step of finely dispersing carbon black of 100 g or less in an aqueous medium; and a step of oxidizing the carbon black using a hypohalite.
[0006]
In the above Patent Documents 7 and 8, carbon black is oxidized to generate a large number of hydrophilic active hydrogen-containing functional groups on the surface, whereby water dispersibility is good, and aqueous solution having excellent long-term dispersion stability is obtained. This is to obtain a pigment ink. However, in order for carbon black to disperse in water and maintain a stable dispersion state, the amount of hydrophilic functional groups present at the contact interface between the surface of the carbon black particles and the water molecules greatly functions, and merely the carbon black unit weight It is difficult to accurately judge the quality of the dispersibility only by regulating the amount of the functional group present per hit. That is, there are various varieties of carbon black having different specific surface areas. For example, even if the amount of functional groups present in 1 g of carbon black is the same, the contact interface with water molecules that greatly affects the dispersion performance in water is increased. The amount of these functional groups present varies greatly depending on the specific surface area.
[0007]
Accordingly, the present applicant has focused on the amount of hydrophilic hydrogen-containing functional groups present per unit surface area of carbon black as a new index for accurately judging the quality of dispersion performance, and has conducted research on hydrogen-containing functional groups present on the surface. The total amount of carboxyl groups and hydroxyl groups among the groups is 3 μeq / m per unit surface area.²The above-described easily water-dispersible carbon black and a method for producing the same (Patent Document 9) have been developed and proposed.
[0008]
In addition, the formation of a hydrophilic functional group only on the surface of carbon black enhances the dispersibility of carbon black in water, and there is a limit in maintaining long-term dispersion stability. As a result, it was found that the dispersing performance such as easy dispersibility in water and dispersion stability was closely related to the aggregation form of the carbon black particles.₂SA) is 80m²/ G, a carbon black having a DBP oil absorption of 70 ml / 100 g or less, which is an oxidized carbon black, and a ratio Dupa of the Stokes mode diameter Dst (nm) of the aggregate to the average particle diameter Dupa (nm) of the agglomerate. A water-dispersible carbon black having a Dst value of 1.5 to 2.0 (Patent Document 10) was proposed.
[0009]
However, in order to use carbon black as a pigment for an aqueous black ink, for example, a pigment for a printer ink, not only can it be easily dispersed in water and a stable dispersed state can be maintained for a long time, but also printing can be performed. It is required to have excellent ink performance such as paper fixing density, print density, ejection stability, light fastness, and storage stability. In general, if carbon black is simply dispersed in water as a black pigment, for example, when the carbon black is used as an ink jet ink pigment, problems such as the sedimentation of carbon black and a decrease in ejection stability occur. This is considered to be due to the fact that carbon black has a wide particle size distribution and the property that large aggregates are easily formed.
[0010]
Accordingly, the present applicant has conducted intensive research on the properties of carbon black suitable as a pigment for aqueous black ink, and has specified the specific surface area, particle diameter, structure, surface properties, particle aggregation form, etc. of carbon black in a wide range, It has been confirmed that excellent water dispersibility and ink performance can be imparted by oxidatively modifying the surface of the black particles. For example, Patent Document 11 discloses a nitrogen adsorption specific surface area (N₂SA) is 50m²/ G or more, DBP oil absorption of 60 ml / 100 g or more, tinting strength (Tint) of 110 or more, and the sum of carboxyl groups and hydroxyl groups present on the surface being 3 μeq / m²As described above, an aqueous pigment ink characterized in that carbon black having the following characteristics is dispersed in an aqueous medium has been proposed.
(1) The ratio (Dupa50% / Dst) between the average particle size Dupa50% (nm) of agglomerate and the Stokes mode diameter Dst (nm) of the aggregate is 1.1 to 2.1.
(2) The value of the average particle diameter Dupa 50% (nm) of agglomerate is 120 to 180 (nm).
(3) The value of the maximum particle size Dupa 99% (nm) of agglomerate is 350 (nm) or less
[0011]
Further, the present applicant has proposed that the nitrogen adsorption specific surface area (N₂SA) is 120m²/ G or more, DBP oil absorption is 80cm³/ 100 g or less, carbon black having a specific coloring power (Tint) of 120 or more is subjected to oxidation treatment, and the amount of hydrogen-containing functional groups on the surface of the carbon black particles is 3 μmol / m²The ratio of Dupa 50% / Dst between the Stokes mode diameter Dst (nm) of the carbon black aggregate and the average particle diameter Dupa 50% (nm) of the agglomerate is 0.8 to 1.1. Particle aggregation properties in which the value of the average particle size Dupa 50% (nm) is 20 to 60 (nm), the value of the maximum particle size Dupa 99% (nm) of agglomerate is 160 (nm) or less, and the precipitation residue ratio is 10 wt% or less. A carbon black pigment for aqueous inks (Patent Document 12), which has a nitrogen adsorption specific surface area (N₂SA) is 200-270m²/ G, iodine adsorption (IA) 190-260 mg / g, N₂SA / IA value is 0.96-1.20, CTAB specific surface area is 170-240 m²/ G, DBP absorption 100-150cm³/ 100g, 24M4DBP absorption 90-120cm³/ 100 g, the atomic ratio of total carbon atoms to total oxygen atoms measured by X-ray photoelectron spectroscopy after chemically modifying carbon black having a coloring power (Tint) of 135 or more (strength of oxygen binding energy / carbon binding energy (Intensity) of 0.1 or more, and a carbon black pigment for water-based ink (Patent Document 13) was developed and proposed.
[0012]
[Patent Document 1]
JP-A-48-18186
[Patent Document 2]
JP-A-57-159856
[Patent Document 3]
JP-A-4-189877
[Patent Document 4]
JP-A-4-359072
[Patent Document 5]
JP-A-5-43759
[Patent Document 6]
JP-A-5-125306
[Patent Document 7]
JP-A-8-3498
[Patent Document 8]
JP-A-8-319444
[Patent Document 9]
JP-A-11-148027
[Patent Document 10]
JP-A-11-148026
[Patent Document 11]
JP 2000-230134 A
[Patent Document 12]
JP 2001-164147 A
[Patent Document 13]
JP 2001-294776 A
[0013]
[Problems to be solved by the invention]
The present invention has been continuously studied, and in particular, focusing on the CTAB specific surface area as a property indicating the particle property of carbon black, and the aggregate void volume Vp as a property indicating the property of the aggregate, and studying the water dispersion performance and the ink performance. As a result, it has been developed, and its purpose is excellent in water dispersion performance and ink performance, and when printing on plain paper, special paper, OHP sheet, art paper, etc., paper fixing density, print quality, Oxidized carbon black, which has high ejection stability, light resistance, storage stability, etc., and is suitable as a black pigment for aqueous inks, its production method, and aqueous black ink in which this oxidized carbon black is dispersed in water. It is to provide an aqueous dispersion.
[0014]
[Means for Solving the Problems]
The oxidized carbon black of the present invention for achieving the above object has a CTAB specific surface area (10%).³m²/ Kg) and the aggregate void volume Vp (10^-3m³/ Kg) is a carbon black satisfying the following relations (1) and (2), and has a carboxyl group content of 2 to 5 μmol / m by peroxodiacid or peroxodiacid salt.²It is characterized in that at least a part of the generated carboxyl group is neutralized with an alkaline solution having a dissociation constant (pKa) of less than 5.
CTAB × Vp <170 (m⁵/ Kg²)… (1)
1 (nm) <Vp / CTAB <10 (nm) (2)
[0015]
In addition, the method for producing an oxidized carbon black of the present invention uses the CTAB specific surface area (10³m²/ Kg) and the aggregate void volume Vp (10^-3m³/ Kg) and carbon black satisfying the following relations (1) and (2) are mixed with an aqueous solution of peroxodiacid or peroxodiacid salt and stirred to reduce the amount of carboxyl groups to 2 to 5 μmol / m2.²After the oxidation treatment, at least a part of the carboxyl groups is neutralized with an alkaline solution having a dissociation constant (pKa) of less than 5, and then residual salts are removed.
CTAB × Vp <170 (m⁵/ Kg²)… (1)
1 (nm) <Vp / CTAB <10 (nm) (2)
[0016]
Further, the aqueous carbon black dispersion of the present invention is an aqueous carbon black dispersion obtained by dispersing the above-mentioned oxidized carbon black in water, and the agglomerate of carbon black in the aqueous dispersion has an average particle size Dupa of 50%. １３０130 nm, the maximum particle size Dupa 99% is 150-320 nm, and the ratio ΔDupa (mode) / Dupa (mode) of the half-width ΔDupa (mode) of the agglomerate to the mode particle size Dupa (mode) is 1.20 or less. It is characterized by having.
However, the average particle size Dupa of agglomerate 50% is calculated by irradiating an aqueous dispersion of carbon black with a laser beam to form a cumulative frequency distribution curve of the agglomerate particle size from the degree of frequency modulation of the scattered light. The particle diameter value of the cumulative frequency is shown, and Dupa 99% indicates the particle diameter value of the 99% cumulative frequency in the same distribution curve. The half width ΔDupa (mode) ｍ indicates a particle size difference between two large and small points corresponding to 頻 度 of the frequency value in the mode diameter Dupa (mode) of the frequency distribution curve of the agglomerate particle diameter.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
The oxidized carbon black of the present invention has a CTAB specific surface area (10³m²/ Kg) and the aggregate void volume Vp (10^-3m³/ Kg) is an essential requirement to use carbon black satisfying the following relationships (1) and (2).
CTAB × Vp <170 (m⁵/ Kg²)… (1)
1 (nm) <Vp / CTAB <10 (nm) (2)
[0018]
The CTAB specific surface area is an index indicating an external specific surface area not including micropores on the surface of carbon black particles, and is more closely related to the particle diameter of carbon black. That is, as the CTAB specific surface area increases, the particle diameter decreases, and the number of carbon black particles per unit weight of carbon black in an aqueous dispersion increases. Therefore, when the carbon black dispersion concentration is the same, the distance between the carbon black particles becomes short, and the viscosity of the aqueous carbon black dispersion increases.
[0019]
The aggregate void volume Vp is the volume of voids of aggregates (aggregates) in which basic fine particles of carbon black are fused and bonded in a three-dimensionally irregular and complex chain shape, and the development of the structure of carbon black It is also an indicator of the degree. That is, as the value of the aggregate void volume Vp increases, the distance between the aggregates becomes shorter, so that a three-dimensional network is easily formed, and more water is occluded in the voids of the network. Therefore, as the structure develops and the aggregate void volume Vp increases, the viscosity of the aqueous carbon black dispersion increases when the dispersion concentration of carbon black is the same.
[0020]
That is, the larger the value represented by CTAB × Vp, the higher the viscosity of the aqueous dispersion becomes, and in the case of using a water-based black ink, for example, the ejection stability decreases. Therefore, the oxidized carbon black of the present invention has a carbon black characteristic of [CTAB specific surface area (10³m²/ Kg)] × [Agglomerate void volume Vp (10^-3m³/ Kg)] is 170 (m⁵/ Kg²) Is applied.
[0021]
On the other hand, when the CTAB specific surface area increases, the particle diameter decreases, so that when the aqueous black ink is used, the carbon black particles easily pass through the gap between the paper fibers, and the blackness decreases. In addition, when the aggregate void volume Vp increases, the developed structure makes it difficult for the carbon black particles to pass through the voids between the paper fibers, thereby increasing the blackness. Therefore, carbon black having a higher value of Vp / CTAB has a higher blackness as an aqueous ink.
[0022]
However, when the CTAB specific surface area is constant and the agglomerate void volume Vp increases, the carbon black particles in the same aqueous dispersion have the same carbon black dispersion concentration, and the distance between the carbon black particles becomes smaller, so that the aggregation of the carbon black particles progresses. Large aggregates (agglomerates) are formed and sedimentation is facilitated.
[0023]
Therefore, in the present invention, a carbon black that satisfies the relationship of [1 (nm) <Vp / CTAB <10 (nm)] as a characteristic of the carbon black is applied. When the value of Vp / CTAB is 1 nm or less, the aggregation of the carbon black in the aqueous dispersion is suppressed, so that the sedimentation is difficult and the dispersibility is good, but the blackness at the time of printing decreases. On the other hand, when the value of Vp / CTAB is 10 nm or more, the blackness at the time of printing is good, but it tends to settle, and the dispersion stability is impaired.
[0024]
In addition, these characteristics are measured by the following methods.
(1) CTAB specific surface area;
JIS K6217 (97) "Test method for basic performance of carbon black for rubber"
[0025]
(2) aggregate void volume Vp;
A dedicated cell (3 cm) of mercury porosimeter (Pore {Sizer 9300}, manufactured by Micromeritics Co., Ltd.) using a carbon black pellet having a particle size of 250 to 500 μm dried according to JIS K6221 (85) “How to prepare a dried sample”.³)), Put a pressure of 25 psi to 30,000 psi, and inject mercury to measure the capacitance (pF picofarad). The capacitance is obtained by measuring the capacitance between mercury inside the cell and an electrode outside the cell, and calculating the amount of mercury injected from the change in the capacitance. The cumulative volume of the pore diameter from 0.0006 to 7.2 μm calculated from the following equation is expressed as Vp (cm³/ G).

However, Vp; Agglomerate void volume (cm³/ G)
X1; Capacitance at 25 psi pressure (pF)
X2}; Capacitance (pF) at a pressure of 30,000 psi
W; Weight (g) for carbon black sample
CF; 定 数 Constant determined by cell
[0026]
The oxidized carbon black of the present invention is intended for a carbon black having a CTAB specific surface area and an aggregate void volume Vp satisfying the above-mentioned relationship, and has a carboxyl group content on the surface of the carbon black particle by peroxodiacid or peroxodiacid salt. 2-5 μmol / m²Is oxidized.
[0027]
In the present invention, as an oxidizing agent for oxidizing carbon black, peroxodiacid or peroxodiacid salt is used in a limited manner. Examples of the peroxodiacid include peroxosulfuric acid, peroxocarbonic acid, and peroxophosphoric acid, and examples of the salt include alkali metal salts and ammonium salts.
[0028]
The reason for limiting the oxidizing agent in this way is that when other oxidizing agents such as hypohalous acid or a salt thereof are used, the halogen remains in the carbon black, and the printed matter using this carbon black as a pigment This is because there is a concern that dioxin and the like will be generated when incinerating waste, which poses an environmental problem. Further, dichromic acid and salts thereof, and permanganic acid and salts thereof also easily cause heavy metals to remain in oxidized carbon black or waste liquid, which may cause a problem of environmental pollution.
[0029]
Oxidation with nitric acid forms a nitroso group on the surface of carbon black, and carbon black having this nitroso group has mutagenicity and is harmful to the human body. In addition, oxidation by hydrogen peroxide has weak oxidizing power, and it is difficult to sufficiently generate a carboxyl group that effectively functions in water dispersibility.
[0030]
Furthermore, in the gas phase oxidation using ozone, a channeling phenomenon occurs, so that a carboxyl group cannot be uniformly generated on the surface of carbon black. Since the oxidizing power is weak, the generation amount of the carboxyl group is small. In the method of oxidizing by bubbling ozone in the liquid phase, the solubility of ozone in water is low, so that the amount of generated carboxyl groups is further reduced.
[0031]
Generally, when carbon black is oxidized, various functional groups such as a carboxyl group (—COOH), a hydroxyl group (—OH), and a quinone group (> C ＝ O) are generated depending on oxidation conditions. Among these functional groups, in order to have a high affinity for water molecules and to form a stable dispersion state in water, the abundances of carboxyl groups and hydroxyl groups, which are acidic functional groups containing active hydrogen, are significantly related. However, the dissociation constant of the hydroxyl group is 8 to 10, which is much larger than 2 to 5 of the carboxyl group, so that the carboxyl group is dominant in the functional group involved in water dispersibility. In addition, the quinone group has a low affinity for water molecules, and rather becomes a factor that hinders dispersibility in water.
[0032]
Therefore, if the amount of the carboxyl group as the functional group present on the surface of the carbon black particles is increased, the dispersibility in water is improved. On the other hand, when the affinity for water is improved, the permeability of the carbon black between the paper fibers is increased, and the blackness tends to decrease when printing is performed. In the process of carbon black being dispersed in water and in the state of being dispersed in water, the amount of hydrophilic functional groups present at the contact interface between carbon black and water molecules exerts an important function. Therefore, the quality of the dispersing performance cannot be accurately evaluated based on the amount of the functional group per unit weight of the carbon black. Therefore, from the viewpoint of achieving both water dispersibility and blackness, the amount of carboxyl groups is adjusted to 2 to 5 μmol / m 2.²Set to.
[0033]
The oxidized carbon black of the present invention is obtained by neutralizing at least a part of the carboxyl groups formed by such liquid phase oxidation with an alkali solution having a dissociation constant (pKa) of less than 5. Neutralization with an alkaline solution having a dissociation constant of 5 or more (eg, sodium hydrogen carbonate, sodium acetate, etc.) makes it difficult to substitute a small but generated hydroxyl group with a phenolate salt, and disperses carbon black in the dispersion. This is because the possibility that the stability becomes unstable with time increases.
[0034]
Examples of the alkaline solution having a dissociation constant (pKa) of less than 5 include, for example, lithium hydroxide, sodium hydroxide, and potassium hydroxide as the inorganic system, and tetramethylammonium hydroxide and tetraethylammonium hydroxide as the organic system. Is done.
[0035]
The method for producing the oxidized carbon black of the present invention comprises a CTAB specific surface area (10³m²/ Kg) and the aggregate void volume Vp (10^-3m³/ Kg) and (1), (2) CTAB × Vp <170 (m⁵/ Kg²)… (1)
1 (nm) <Vp / CTAB <10 (nm) (2)
The carbon black satisfying the above relationship is placed in an aqueous solution of peroxodiacid or peroxodiacid salt, and the mixture is stirred while appropriately controlling the oxidizing agent concentration, the amount of carbon black added, the reaction temperature, the reaction time, the stirring speed, and the like. By doing so, the amount of carboxyl groups can be 2-5 μmol / m²And then neutralizing at least a part of the generated carboxyl groups by adding an alkaline solution having a dissociation constant (pKa) of less than 5, and then removing residual salts.
[0036]
Salts generated by the neutralization are present in the dispersion of oxidized carbon black neutralized with the alkaline solution. Therefore, these residual salts are subjected to electrodialysis or a reverse osmosis membrane, an ultrafiltration membrane, a loose R.R. Oxidized carbon black is purified by separation with a separation membrane such as O. If the residual salt removal is insufficient, the dispersibility, storage stability, viscosity, etc. of the aqueous dispersion will deteriorate, and there will be a problem of equipment corrosion. It is preferable to remove the carbon black so that the electric conductivity is less than 2 mS / cm, with the dispersion concentration of carbon black being 20 wt%.
[0037]
The carboxyl group content is measured by the following method.
(3) carboxyl group;
Concentration 0.976mol / dm³Sodium bicarbonate 0.5dm³After adding 2 to 5 g of carbon black to the mixture and shaking for 6 hours, the carbon black was filtered off from the reaction solution, and the concentration of the filtrate was 0.05 mol / dm.³After adding the hydrochloric acid aqueous solution of 濃度, the concentration is 0.05 mol / dm until the pH becomes 7.0.³Carboxyl groups are quantified by performing a neutralization titration test with an aqueous solution of sodium hydroxide in (4). Next, this measured value is used as the nitrogen adsorption specific surface area (N₂SA; m²/ G) is divided by the amount of carboxyl groups (μmol / m²).
[0038]
The aqueous dispersion of the oxidized carbon black of the present invention is characterized in that the above-mentioned oxidized carbon black is dispersed in water and subjected to a classification treatment to specify the particle aggregation form of the carbon black. When carbon black is dispersed in water, it is easy to disperse in water, and in order to maintain a stable dispersion state, carbon black particles are dispersed in water in a finer aggregated form and reagglomerated to form a larger aggregate. Advantageously, it is difficult to form aggregates. On the other hand, when the aggregation form of the carbon black particles is small, it is advantageous for improving the dispersing performance.However, when the aqueous ink is used, the carbon black easily passes through the gap between the paper fibers, and the paper fixing density is reduced, and the black is reduced. The degree becomes lower. However, when the form of aggregation becomes large, the dispersibility is reduced, and the ejection stability and the filterability of the ink are deteriorated.
[0039]
Furthermore, the particle aggregate of the raw material carbon black has a particle size distribution, and the particle size distribution of the oxidized carbon black naturally has a particle size distribution.For example, a small particle aggregate has insufficient water dispersibility due to insufficient oxidation. In addition to being present, they also contain large aggregates that tend to settle. Therefore, it is necessary to selectively remove those having insufficient oxidation and those having a large particle size. As a means for selective removal, there is a classification treatment, for example, a method by centrifugation, separation by a functional membrane, or the like.
[0040]
In other words, the aqueous dispersion of the oxidized carbon black of the present invention is intended to sharpen the particle size distribution of the particle aggregate of the carbon black in the aqueous dispersion, that is, the agglomerate particle size, by the classification treatment. In the body, the average particle diameter Dupa of carbon black agglomerate 50% is 50 to 130 nm, the maximum particle diameter Dupa 99% is 150 to 320 nm, and the ratio ΔDupa (mode) of the half width ΔDupa (mode) of the agglomerate to the mode particle diameter Dupa (mode)} ) {/ Dupa (mode)} is subjected to classification processing to 1.20 or less. The dispersion concentration of carbon black is preferably adjusted to 50% by weight or less. If the dispersion concentration exceeds 50% by weight, the carbon black tends to re-agglomerate in the dispersion, and it tends to be difficult to maintain stable dispersion for a long period of time.
[0041]
If the value of the average particle diameter Dupa 50% of the agglomerate is less than 50 nm, for example, when a water-based ink is prepared and printed on paper, the ratio of carbon black passing through the gap between the paper fibers increases, and the paper fixing density, that is, the blackness Decreases. On the other hand, when it exceeds 130 nm, the blackness is improved because the amount of carbon black captured on the paper fiber surface is increased, but the dispersion stability is reduced, the filterability and the ejection stability from the ink nozzle are reduced, and the precipitation residue is reduced. This causes problems such as an increase in the rate. Further, when the value of the maximum particle size Dupa 99% of agglomerate is less than 150 nm, the blackness decreases, and when it exceeds 320 nm, the filterability, the discharge stability decreases, and the sediment residue ratio increases remarkably. Further, by adjusting the value of the ratio ΔDupa {(mode) / Dupa (mode)} of the half width ΔDupa (mode) of the agglomerate and the mode particle size Dupa (mode) to 1.20 or less by classification processing, the filterability and discharge are improved. The stability is improved, and the precipitation residue rate can be reduced.
[0042]
Dupa 50%, Dupa 99%, Dupa (mode) {, and ΔDupa (mode)} are measured by the following methods.
(4) Measurement of Dupa 50%, Dupa 99%, Dupa (mode) {, ΔDupa (mode)};
0.1 to 0.5 kg / m by dispersing carbon black in water³Is prepared, and the dispersion is irradiated with laser light using a heterodyne laser Doppler type particle size distribution analyzer (UPA mode1 9340, manufactured by Microtrac Co., Ltd.), and the dispersion in the dispersion is determined from the degree of frequency modulation of the scattered light. Measure the particle size of the agglomerate. The carbon black in the dispersion liquid undergoes Brownian motion, and the frequency of the scattered light is modulated by the size of the dispersed carbon black aggregate due to the Doppler effect. Therefore, since the intensity of the Brownian motion varies depending on the size of the aggregate, the size of the aggregate in a state of being dispersed in water, that is, the particle size of the agglomerate can be measured.
[0043]
From the agglomerate particle size measured in this way, a cumulative frequency distribution curve is created, and the value of 50% cumulative frequency is the average particle size Dupa of agglomerate 50% (nm), and the value of 99% cumulative frequency is the maximum particle size of agglomerate. Dupa: 99% (nm). Further, a frequency distribution curve is created from the measured agglomerate particle diameter, a mode diameter Dupa (mode) (nm) is obtained from the frequency distribution curve, and a magnitude corresponding to の of the frequency value in the mode diameter is obtained. The particle size difference between the two points is determined, and the half-value width ΔDupa (mode) (nm).
[0044]
When the oxidized carbon black aqueous dispersion of the present invention is used as an aqueous black ink or the like, for example, the electric conductivity when the carbon black dispersion concentration is adjusted to 20 wt% is less than 2 mS / cm. preferable. Unneutralized salts and the like are present in the classified aqueous dispersion of carbon black. If these salts are present in a large amount, the carbon black will aggregate and precipitate due to salting out. As a method for desalination purification, purification and filtration are performed using a functional membrane such as an ultrafiltration membrane, a reverse osmosis membrane, or electrodialysis, and the electric conductivity is set to 2 mS / cm so that a stable dispersion state can be maintained for a long time. Adjusted to less than. If the electric conductivity of the aqueous dispersion is 2 mS / cm or more, aggregation of carbon black occurs due to the effect of salts such as humates eluted from the carbon black during long-term storage, resulting in an increase in viscosity and dispersion. Stability may decrease. In addition, when the ink medium is used, there may be a problem that the apparatus, the machine, and the like are corroded.
[0045]
Further, when used as an ink for a recording liquid for inkjet, for example, the dispersion concentration of carbon black is 20 wt%, the viscosity at 25 ° C. is 10 mPa · s or less, the specific gravity is 1.3 or less, the surface tension is 60 mN / m or more, It is used after adjusting to properties such as pH 4 to 9 and precipitation residue rate of less than 40 wt%.
[0046]
That is, when the viscosity exceeds 10 mPa · s, clogging of the printer head is apt to occur, and the ejection stability of the ink is reduced. When the specific gravity exceeds 1.30, thixotropic conversion is likely to occur. If the surface tension is less than 60 mN / m, the print quality will be impaired due to the wetting of the nozzle tip and the like, and if the pH is less than 4, the viscosity will increase and the dispersion stability will deteriorate. If it exceeds, the water resistance will decrease when printing, and the viscosity will increase due to heating. On the other hand, if the precipitation residue ratio of the aqueous dispersion exceeds 40% by weight, the dispersion stability is significantly reduced. The carbon black content in the aqueous dispersion according to the present invention was set to 4% by weight, diluted with pure water, and drawn to copy paper (Xerox 4024 paper) with a # 6 bar coater to obtain a blackness (light density) of 1.40 or more. And a sufficient print density can be obtained.
[0047]
As described above, the aqueous dispersion obtained by dispersing the oxidized carbon black of the present invention in water has excellent dispersion stability over time, and also has good water resistance and light resistance. Can be suitably used.
[0048]
Hereinafter, examples of the present invention will be specifically described in comparison with comparative examples.
[0049]
Examples 1-2, Comparative Examples 1-2
100 g of carbon black having different CTAB specific surface area and aggregate void volume Vp shown in Table 1 was mixed at a concentration of 1.0 mol / dm.³Sodium peroxodisulfate aqueous solution 3dm³, Reaction temperature 333k, stirring speed 0.12０．１s^-1The mixture was stirred and mixed under the conditions described above for 10 hours to perform oxidation treatment. Next, the oxidized carbon black separated by filtration was dispersed in pure water to obtain a concentration of 1.0 mol / dm.³And neutralized with an aqueous solution of sodium hydroxide. After neutralization, a centrifuge (Hitachi Koki Co., Ltd. CR22F) 7.5 × 10^-3s^-1Classification was performed at a rotation speed of 15 minutes. Thereafter, the remaining salt was separated from the supernatant by an ultrafiltration membrane (AHP-1010, manufactured by Asahi Kasei Corporation, molecular weight cut off: 50,000), and then water was removed so that the carbon black dispersion concentration became 20 wt%. The electrical conductivity of the oxidized carbon black aqueous dispersion was 1.3 mS / cm.
[0050]
Comparative Example 3
100 g of the same carbon black as in Example 1 was used at a concentration of 1.0 mol / dm.³3dm aqueous solution of potassium permanganate³At a reaction temperature of 343k and a stirring speed of 0.12 s^-1After neutralization, classification, and residual salt separation in the same manner as in Example 1, except that the mixture was oxidized by stirring and mixing for 3 hours under the conditions described above, water was removed to oxidize the dispersion to a concentration of 20 wt%. An aqueous dispersion of carbon black was produced. The electric conductivity of this aqueous dispersion was 1.5 mS / cm.
[0051]
Comparative Example 4
100 g of the same carbon black as in Example 1 was added to an aqueous solution of sodium hypochlorite having an effective chlorine concentration of 4% in an aqueous solution of 3 dm.³At a reaction temperature of 373k and a stirring speed of 0.12 s^-1After neutralizing, classifying, and separating residual salts by the same method as in Example 1 except that the mixture was oxidized by stirring and mixing for 5 hours under the conditions described in Example 1, water was removed. Thus, an aqueous dispersion of oxidized carbon black having a dispersion concentration of 20 wt% was produced. The electric conductivity of this aqueous dispersion was 1.2 mS / cm.
[0052]
Comparative Example 5
100 g of the same carbon black as in Example 1 was placed in an ozonizer and oxidized for 1 hour under the conditions of an ozone generator (manufactured by Japan Ozone Co., IOT-4A6) at a generation voltage of 200 V and an ozone generation amount of 18 g / h. After neutralization treatment, classification treatment, and residual salt separation treatment in the same manner as in Example 1, water was removed to produce an aqueous dispersion of oxidized carbon black having a dispersion concentration of 20 wt%. The electric conductivity of this aqueous dispersion was 0.8 mS / cm.
[0053]
Comparative Example 6
The concentration of the aqueous solution of sodium peroxodisulfate is 2.0 mol / dm³After performing oxidation treatment, neutralization treatment, classification treatment, and residual salt separation treatment in the same manner as in Example 1, water was removed to obtain an aqueous dispersion of oxidized carbon black having a dispersion concentration of 20 wt%. Manufactured. The electric conductivity of this aqueous dispersion was 0.8 mS / cm.
[0054]
Comparative Example 7
The neutralization treatment after the oxidation treatment is performed at a concentration of 1.0 mol / dm.³Except for neutralization with an aqueous solution of thorium bicarbonate, the same oxidation treatment, classification treatment and residual salt treatment were performed in the same manner as in Example 1 and then water was removed to disperse an oxidized carbon black having a dispersion concentration of 20 wt% in water. Body manufactured. The electric conductivity of this aqueous dispersion was 1.2 mS / cm.
[0055]
Comparative Example 8
Oxidation, neutralization, classification, and residual salt separation were performed in the same manner as in Example 1 except that classification was not performed, and then water was removed to remove water from the oxidized carbon black having a dispersion concentration of 20 wt%. A dispersion was produced. The electric conductivity of this aqueous dispersion was 1.2 mS / cm.
[0056]
The aqueous dispersions of the oxidized carbon black thus produced are shown in Tables 1 and 2 in comparison with the production conditions.
[0057]
[Table 1]

Table notes;
* 1 @A; Na₂S₂O₈
B: KMnO₄
[0058]
[Table 2]

Table notes;
* 1 @A; Na₂S₂O₈
C: NaClO
D; O₃
* 2: Available chlorine concentration: 4%
[0059]
Next, the average particle size Dupa of carbon black agglomerates in the aqueous dispersion of these carbon blacks is 50% (nm), the maximum particle size is Dupa, 99% (nm), the mode particle size is Dupa (mode) (nm), and the half width is ΔDupa (mode) (nm) was measured. The water dispersion performance and the ink performance were evaluated by the following methods. Tables 3 and 4 show the obtained results.
[0060]
Storage stability;
The sample was put in a closed container, kept at a temperature of 70 ° C., and the viscosity after each lapse of 1 to 4 weeks was measured to compare the storage stability. The viscosity was measured with a rotational vibration type viscometer [VM-100A-L #, manufactured by Yamaichi Electric Co., Ltd.].
[0061]
Agglomerate particle size;
The sample was placed in a closed container, kept at a temperature of 70 ° C., and the particle size of agglomerate after 1 to 4 weeks had elapsed was measured, and the change was compared.
[0062]
Filterability;
The sample was filtered using filter paper (No. 2 manufactured by Advantech TOYO No. 2) and a filter having a membrane pore size of 3 μm, 0.8 μm, 0.65 μm, 0.45 μm to 2.66 × 10 6.³A filtration test was performed under a reduced pressure of Pa, and the amount of passing was measured.
[0063]
Precipitation residue rate;
The weight ratio (M 1 / M 0) of the amount of the precipitate residue (M 1) after centrifuging the sample for 30 minutes at a gravitational acceleration of 20000 G and the weight of carbon black (M 0) before centrifugation. Was defined as the precipitation residue ratio.
[0064]
Print density;
The carbon black aqueous dispersion was diluted to a carbon black dispersion concentration of 4 wt%, printed on a copy paper (XEROX # 4024) with a # 6 bar coder, and the optical density was measured using a Macbeth densitometer ({RD-927}, manufactured by Colmorgen). .
[0065]
[Table 3]

[0066]
[Table 4]

[0067]
From the results in Tables 1 to 4, the aqueous dispersions of Examples 1 and 2 have excellent storage stability, filterability, precipitation residue ratio, print density and the like in a well-balanced manner, but the Vp / CTAB of carbon black is large. Comparative Example 1 has a remarkably large precipitation residue ratio, and Comparative Example 2 in which the CTAB × Vp value of carbon black is large has a high initial viscosity.
[0068]
Comparative Example 3 using potassium permanganate as the oxidizing agent has a large amount of residual heavy metals, and Comparative Example 4 using sodium hypochlorite as the oxidizing agent has a large amount of residual halogens. Absent.
[0069]
In Comparative Example 5 in which ozone was used as the oxidizing agent, carbon black was not sufficiently oxidized due to the low oxidizing power of ozone, so that the dispersion performance and the filterability were significantly reduced. When the amount of the carboxyl group increases, the water dispersibility is excellent, but the print density is low.
[0070]
In Comparative Example 7 neutralized with sodium bicarbonate, the water dispersibility is reduced, and in the water dispersion of Comparative Example 8 in which the classification treatment is not performed, the filterability is significantly reduced.
[0071]
【The invention's effect】
As described above, according to the present invention, an oxidized carbon black excellent in water dispersibility and a method for producing the same are provided, and according to the aqueous dispersion of the present invention in which the oxidized carbon black is dispersed in water. It has good long-term stability of dispersibility such as filterability, percentage of sedimentation residue, and high print density, and is expected to have excellent practicality as a water-based ink including ink jet printers.

Claims (3)

The carbon black having a CTAB specific surface area (10 ³ m ² / kg) and an aggregate void volume Vp (10 ⁻³ m ³ / kg) satisfying the following relations (1) and (2): The carboxyl group is oxidized to ² to 5 μmol / m ² with diacid or peroxodiacid salt, and at least a part of the generated carboxyl group is neutralized with an alkali solution having a dissociation constant (pKa) of less than 5. An oxidized carbon black characterized by the following.
CTAB × Vp <170 (m ⁵ / kg ² ) (1)
1 (nm) <Vp / CTAB <10 (nm) (2) The carbon black which satisfies the following relations (1) and (2) with CTAB specific surface area (10 ³ m ² / kg) and aggregate void volume Vp (10 ⁻³ m ³ / kg) is peroxodiacid or After mixing and stirring with an aqueous solution of peroxodiacid salt to oxidize the amount of carboxyl groups to ² to 5 μmol / m ² , at least a part of carboxyl groups is neutralized with an alkali solution having a dissociation constant (pKa) of less than 5, The method for producing an oxidized carbon black according to claim 1, wherein the residual salt is removed.
CTAB × Vp <170 (m ⁵ / kg ² ) (1)
1 (nm) <Vp / CTAB <10 (nm) (2) An aqueous dispersion in which the oxidized carbon black according to claim 1 is dispersed in water, wherein the average particle diameter Dupa of the agglomerates of the carbon black in the aqueous dispersion is 50 to 130 nm, and the maximum particle diameter Dupa is 150 to 130 nm. Oxidized carbon black water characterized by having been subjected to classification treatment at 320 nm and a ratio ΔDupa (mode) / Dupa (mode) of the half-value width ΔDupa (mode) of the agglomerate to the mode particle size Dupa (mode) of 1.20 or less. Dispersion.
However, the average particle size Dupa of agglomerate 50% is calculated by irradiating an aqueous dispersion of carbon black with a laser beam to form a cumulative frequency distribution curve of the agglomerate particle size from the degree of frequency modulation of the scattered light. The particle diameter value of the cumulative frequency is shown, and Dupa 99% indicates the particle diameter value of the 99% cumulative frequency in the same distribution curve. The half width ΔDupa (mode) indicates a particle size difference between two large and small points corresponding to 頻 度 of the frequency value in the mode diameter Dupa (mode) of the frequency distribution curve of the agglomerate particle diameter.