JP4484357B2 - Magnetic toner, image forming method using the magnetic toner, and process cartridge - Google Patents

Description

Ｖ）無機微粉体をトナー粒子表面に有し、ＶＩ）該結着樹脂成分は、スチレンモノマーを少なくとも含む単量体を有機系過酸化物を用いて重合させて得られる重合体を少なくとも含有することを特徴とする磁性トナー、該トナーを用いた画像形成方法及びプロセスカートリッジである。
【００４４】
【発明の実施の形態】
＜１＞本発明の磁性トナー
本発明の磁性トナーは、少なくとも結着樹脂成分及び酸化鉄を含有しているトナー粒子を有する。
【００４５】
本発明者らは、これまでの磁性トナーの帯電の均一化および安定化について鋭意検討した結果、Ｘ線光電子分光分析により測定される磁性トナーの表面に存在する炭素元素の含有量（Ａ）に対する鉄元素の含有量（Ｂ）の比（Ｂ／Ａ）を0.001未満とし、さらに下記式（２）により求められる円形度から計算される該トナーの平均円形度を0.970以上とすることが、トナーの帯電性の均一化および安定化に極めて有効であることを見出し、本発明に到達したものである。
【００４６】
【数３】

（式中、Ｌ₀は、粒子像と同じ投影面積をもつ円の周囲長を示し、Ｌは、粒子の投影像の周囲長を示す。）
また、上記の様なトナーを用いることにより、トナーの回収不良に伴うゴースト画像の発生しやすいクリーナレス構成や接触帯電を組み合わせた画像形成方法や、接触帯電工程と一成分非接触現像工程と接触転写工程とを含む画像形成方法においても、感光体の削れ、帯電不良や転写不良が著しく抑制され、長期間の使用においてもカブリその他の画像欠陥の無い高精細な画像が安定して得られることを見出し、本発明に到達したものである。
【００４７】
これは、従来より一般に用いられる磁性酸化鉄を用いた磁性トナーでは達成が困難であったものである。
【００４８】
その理由は、用いる磁性酸化鉄を十分且つ均一に疎水化できていなかったことに起因する。
【００４９】
磁性トナーを製造するときには、表面が疎水化処理された磁性酸化鉄を用いることにより、トナー結着樹脂成分中への磁性酸化鉄粒子の分散性を向上することができる。また、トナー粒子表面に磁性酸化鉄が多く露出している場合にも、磁性酸化鉄の表面が均一に疎水化処理されていればどのような環境下においてもトナーの帯電性能を損ないにくくなる。
【００５０】
そこで以前より、磁性酸化鉄の表面を疎水化する方法が種々提案されている。しかしながらこれまでの方法では、十分に且つ均一に疎水化された磁性酸化鉄はなかなか得られにくい。また、処理剤等を多量に使用したり、高粘性の処理剤等を使用した場合、疎水化度は確かに上がるものの、粒子同士の合一等が生じ、疎水性と分散性の両立は必ずしも達成されていない。
【００５１】
一般に、未処理の酸化鉄表面は親水性を有しているので、疎水性の酸化鉄を得るには、親水性の酸化鉄を疎水化する必要があるが、これまでの表面処理法では疎水化の均一性が不十分であり、そのような酸化鉄を用いた従来のトナーは湿度などに応じて帯電性が変動してしまい、安定性に欠ける。
【００５２】
これに対し、本発明のトナーにおいて磁性体として使用される酸化鉄は、非常に高いレベルでの疎水化の均一性が図られているものである。具体的には、例えば、酸化鉄を疎水化する際、水系媒体中で、酸化鉄を一次粒径となるよう分散しながらカップリング剤を加水分解しながら表面処理することによって得られる酸化鉄である。水系媒体中での疎水化処理方法は、気相中での処理に比べ、酸化鉄粒子同士の合一が生じにくく、また疎水化処理による酸化鉄粒子間の帯電反発作用が働き、酸化鉄はほぼ一次粒子の状態で表面処理されるようになるため、高い均一性の疎水化が達成される。
【００５３】
カップリング剤を水系媒体中で加水分解しながら酸化鉄表面を処理する方法は、クロロシラン類やシラザン類のようにガスを発生するようなカップリング剤を使用する必要もなく、さらに、これまで気相中では酸化鉄粒子同士が合一しやすくて、良好な処理が困難であった高粘性のカップリング剤も使用できるようになり、疎水化の効果は絶大である。
本発明に使用できるカップリング剤としては、例えば、シランカップリング剤、チタンカップリング剤が挙げられる。より好ましく用いられるのはシランカップリング剤であり、下記一般式（I）で示されるものである。
【００５４】
【化１】
Ｒ_mＳｉＹ_n （I）
（式中、Ｒはアルコキシ基を示し、ｍは１〜３の整数を示し、Ｙはアルキル基、ビニル基、グリシドキシ基、メタクリル基等の炭化水素基を示し、ｎは１〜３の整数を示す。但し、ｍ＋ｎ＝４である。）
上記一般式（I）で表されるシランカップリング剤としては、例えばビニルトリメトキシシラン、ビニルトリエトキシシラン、γ−メタクリルオキシプロピルトリメトキシシラン、ビニルトリアセトキシシラン、メチルトリメトキシシラン、メチルトリエトキシシラン、イソブチルトリメトキシシラン、ジメチルジメトキシシラン、ジメチルジエトキシシラン、トリメチルメトキシシラン、ヒドロキシプロピルトリメトキシシラン、フェニルトリメトキシシラン、ｎ−ヘキサデシルトリメトキシシラン、ｎ−オクタデシルトリメトキシシランを挙げることができる。
特に、下記一般式（II）で示されるアルキルトリアルコキシシランカップリング剤を使用して水系媒体中で酸化鉄を疎水化処理するのが良い。
【００５５】
【化２】
Ｃ_pＨ_2p+1−Ｓｉ−（ＯＣ_qＨ_2q+1）₃
（式中、ｐは２〜２０の整数を示し、ｑは１〜３の整数を示す）
上記式におけるｐが２より小さいと、疎水化処理は容易となるが、疎水性を十分に付与することが困難な場合があり、またｐが２０より大きいと、疎水性は十分になるが、酸化鉄粒子同士の合一が多くなり、トナー中へ酸化鉄粒子を十分に分散させることが困難な場合がある。
【００５６】
また、ｑが３より大きいと、シランカップリング剤の反応性が低下して疎水化が十分に行われにくくなる。
【００５７】
特に、式中のｐが２〜２０の整数（より好ましくは、３〜１５の整数）を示し、ｑが１〜３の整数（より好ましくは、１又は２の整数）を示すアルキルトリアルコキシシランカップリング剤を使用するのが良い。
【００５８】
その処理量は酸化鉄100質量部に対して、0.05〜20質量部、好ましくは0.1〜10質量部とするのが良い。
【００５９】
本発明において、水系媒体とは、水を主要成分としている媒体である。具体的には、水系媒体として水そのもの、水に少量の界面活性剤を添加したもの、水にｐＨ調整剤を添加したもの、水に有機溶剤を添加したものが挙げられる。界面活性剤としては、ポリビニルアルコール等のノンイオン系界面活性剤が好ましい。界面活性剤は、水に対して0.1〜5質量％添加するのが良い。ｐＨ調整剤としては、塩酸等の無機酸が挙げられる。
【００６０】
撹拌は、例えば撹拌羽根を有する混合機（具体的には、アトライター、ＴＫホモミキサー等の高剪断力混合装置）で、酸化鉄粒子が水系媒体中で、一次粒子になるように充分におこなうのが良い。
こうして得られる酸化鉄は表面が均一に疎水化処理されているため、トナー材料として用いた場合、トナー中への分散性が非常に良好であり、しかもトナー表面からの露出が無い。
従って、こういった酸化鉄を用いることにより、Ｘ線光電子分光分析により測定されるトナーの表面に存在する炭素元素の含有量（Ａ）に対する鉄元素の含有量（Ｂ）の比（Ｂ／Ａ）が0.001未満という本発明のトナーを得ることが可能となり、トナーの帯電の均一性及び安定化が達成でき、このトナーを用いることによって、高画質及び高耐久安定性が達成できる。さらには、（Ｂ／Ａ）を0.0005未満とすることで、帯電性及び安定性がより一層向上する。
【００６１】
また、本発明のトナーにおいて磁性体として用いられる酸化鉄は、リン、コバルト、ニッケル、銅、マグネシウム、マンガン、アルミニウム、ケイ素等の元素を含んでもよく、四三酸化鉄、γ−酸化鉄を主成分とするものであり、これらを１種または２種以上を併用して用いられる。これら酸化鉄は、窒素吸着法によるＢＥＴ比表面積が好ましくは2〜30m²/g、特に3〜28m²/gであり、更にモース硬度が5〜7のものが好ましい。
【００６２】
また、酸化鉄の形状としては、８面体、６面体、球状、針状、鱗片状などがあるが、８面体、６面体、球状、不定形の如き異方性の少ないものが画像濃度を高める上で好ましい。こういった形状は、ＳＥＭなどによって確認することができる。
酸化鉄の粒度としては、0.03μm以上の粒径を有する粒子を対象とした粒度の測定において、体積平均粒径が、0.1〜0.3μmであり、かつ0.03〜0.1μmの粒子が40個数％以下であることが好ましい。
【００６３】
体積平均粒径が0.1μm未満の酸化鉄を用いた磁性トナーから画像を得ると、画像の色味が赤味にシフトし、画像の黒色度が不足したり、ハーフトーン画像ではより赤味が強く感じられる傾向が強くなるなど、一般的に好ましいものではない。また、酸化鉄の表面積が増大するために分散性が低下し、製造時に要するエネルギーが増大し、効率的ではない。また、酸化鉄の着色剤としての効果が弱くなり、画像の濃度が不足することもあり、好ましいものではない。
【００６４】
一方、酸化鉄の体積平均粒径が0.3μmを超えると、一粒子あたりの質量が大きくなるため、製造時に結着樹脂成分との比重差の影響でトナー表面に露出する確率が高まったり、製造装置の摩耗などが著しくなる可能性が高まったり、分散物の沈降安定性などが低下するため好ましくない。
【００６５】
また、トナー中において、該酸化鉄の0.1μm以下の粒子が40個数％を超えると、酸化鉄の表面積が増大して分散性が低下し、トナー中にて凝集塊を生じやすくなりトナーの帯電性を損なったり、着色力が低下したりする可能性が高まるため40個数％以下であることが好ましい。さらに、30個数％以下とすると、その傾向はより小さくなるため、より好ましい。
これらの酸化鉄の磁気特性としては、磁場795.8kA/m下で飽和磁化が10〜200Am²/kg、残留磁化が1〜100Am²/kg、抗磁力が1〜30kA/mであるものが用いられる。
【００６６】
なお、酸化鉄の体積平均粒径は、透過型電子顕微鏡（ＴＥＭ）を用いて測定できる。具体的には、測定するトナーの粉体サンプルを透過型電子顕微鏡（ＴＥＭ）で観察し、視野中の100個の酸化鉄粒子径を測定して、体積平均粒径を求める。
【００６７】
前述のＴＥＭによる具体的な観察方法としては、常温硬化性のエポキシ樹脂中へ観察すべき粒子を十分に分散させた後、温度40℃の雰囲気中で２日間硬化させ得られた硬化物を、ダイヤモンド歯を備えたミクロトームにより薄片状のサンプルとして観察する方法が例示される。
【００６８】
比表面積はＢＥＴ法に従って、比表面積測定装置オートソーブ１（湯浅アイオニクス社製）を用いて試料表面に窒素ガスを吸着させ、ＢＥＴ多点法を用いて比表面積を算出することにより得ることができる。
本発明のトナーに用いられる酸化鉄は、例えば下記方法で製造される。
【００６９】
硫酸第一鉄水溶液に、鉄成分に対して当量または当量以上の水酸化ナトリウム等のアルカリを加え、水酸化第一鉄を含む水溶液を調製する。調製した水溶液のｐＨをｐＨ７以上（好ましくはｐＨ８〜１０）に維持しながら空気を吹き込み、水溶液を70℃以上に加温しながら水酸化第一鉄の酸化反応をおこない、磁性酸化鉄粒子の芯となる種晶をまず生成する。
【００７０】
次に、種晶を含むスラリー状の液に、前に加えたアルカリの添加量を基準として約１当量の硫酸第一鉄を含む水溶液を加える。液のｐＨを６〜１０に維持しながら空気を吹込みながら水酸化第一鉄の反応をすすめ種晶を芯にして磁性酸化鉄粒子を成長させる。酸化反応がすすむにつれて液のｐＨは酸性側に移行していくが、液のｐＨは６未満にしない方が好ましい。酸化反応の終期に液のｐＨを調整し、磁性酸化鉄が一次粒子になるよう十分に撹拌し、カップリング剤を添加して十分に混合撹拌し、撹拌後に濾過し、乾燥し、軽く解砕することで疎水化処理磁性酸化鉄粒子が得られる。あるいは、酸化反応終了後、洗浄、濾過して得られた酸化鉄粒子を、乾操せずに別の水系媒体中に再分散させた後、再分散液のｐＨを調整し、十分撹拌しながらシランカップリング剤を添加し、カップリング処理を行っても良い。
【００７１】
いずれにせよ、水溶液中で生成した未処理の酸化鉄粒子を、乾燥工程を経る前の含水スラリーの状態で疎水化することが肝要である。これは、未処理の酸化鉄粒子をそのまま乾燥してしまうと粒子同士の凝集による合一が避けられず、こういった凝集状態の粉末にたとえ湿式疎水化処理を行なっても均一な疎水化処理が難しいためであり、このような表面処理酸化鉄を用いたトナーでは、本発明の磁性トナーの特徴である、Ｂ／Ａ＜0.001を達成することは困難だからである。
【００７２】
第一鉄塩としては、一般的に硫酸法チタン製造に副生する硫酸鉄、鋼板の表面洗浄に伴って副生する硫酸鉄の利用が可能であり、更に塩化鉄等が可能である。水溶液法による磁性酸化鉄の製造方法は一般に反応時の粘度の上昇を防ぐこと、及び、硫酸鉄の溶解度から鉄濃度0.5〜2mol/リットルが用いられる。硫酸鉄の濃度は一般に薄いほど製品の粒度が細かくなる傾向を有する。また、反応に際しては、空気量が多い程、そして反応温度が低いほど微粒化しやすい。
【００７３】
このようにして製造された疎水化処理酸化鉄粒子をトナーに使用することにより、画像特性及び安定性に優れた本発明のトナーを得ることが可能となる。
【００７４】
なお、特公昭60-3181号公報においても、表面をシランカップリング剤で湿式処理した磁性体微粒子を含有する磁性重合トナーの製造方法が開示されている。
【００７５】
しかしながら、特公昭60-3181号公報は、乾燥粉末状の未処理磁性体をシランカップリング剤で湿式表面処理することに関して記載しているものである。
こういった未処理の乾燥磁性体粉末は、乾燥時の一次凝集による粒子同士の合一が避けられないため、湿式表面処理を行なっても個々の磁性体粒子の均一な疎水化は困難である。従ってこのような表面処理磁性体を用いて重合トナーを製造しても、本発明に係るトナーの特徴であるＢ／Ａ＜0.001を達成することは困難である。
【００７６】
トナーの投影面積相当径をＣとし透過型電子顕微鏡（ＴＥＭ）を用いた該トナーの断面観察における酸化鉄とトナー粒子表面との距離の最小値をＤとしたとき、Ｄ／Ｃ≦0.02の関係を満たすトナーの個数が５０％以上であることもまた、本発明のトナーの特徴の一つである。
【００７７】
本発明においては、Ｄ／Ｃ≦0.02の関係を満たすトナー数が50％以上であり、65％以上が好ましく、75％以上がさらに好ましい。
【００７８】
Ｄ／Ｃ≦0.02の関係を満たすトナー数が50％未満の場合には、過半数のトナーにおいて少なくともＤ／Ｃ＝0.02境界線よりも外側には磁性粒子が全く存在しないことになる。仮にこのような粒子を球形として想定すると、１つのトナー粒子を全空間とした場合に酸化鉄の存在しない空間は、トナー粒子の表面に少なくとも11.5％は存在することになる。実際には、最近接位置に酸化鉄が均一に整列してトナー粒子内部に内壁を作るように存在するわけではないので12％以上になることは明らかである。この様な粒子から構成されるトナーにおいては、前述の如き様々な弊害が生じやすい。
【００７９】
本発明において、ＴＥＭによる具体的なＤ／Ｃの測定方法としては、常温硬化性のエポキシ樹脂中へ観察すべき粒子を十分に分散させた後に温度40℃の雰囲気中で２日間硬化させ得られた硬化物を、そのまま、あるいは凍結してダイヤモンド歯を備えたミクロトームにより薄片状のサンプルとして観察する方法が好ましい。
【００８０】
該当するトナー数の割合の具体的な決定方法については、以下のとおりである。
ＴＥＭにてＤ／Ｃを決定するためのトナーは、顕微鏡写真での断面積から円相当径を求め、その値がコールターカウンターを用いる後述の方法により求めた数平均粒径の±10％の幅に含まれるものを該当粒子とし、その該当トナー100個について、酸化鉄粒子表面とトナー粒子表面との距離の最小値（Ｄ）を計測し、Ｄ／Ｃを求め、Ｄ／Ｃ値が0.02以下の粒子の割合を計算する。このときの顕微鏡写真は精度の高い測定を行うために、１〜２万倍の倍率が好適である。本発明では、例えば、透過型電子顕微鏡（日立製Ｈ−６００型）を装置として用い、加速電圧100kVで観察し、拡大倍率が１万倍の顕微鏡写真を用いて観察、測定する。
【００８１】
Ｂ／Ａ＜0.001を満足し、Ｄ／Ｃ≦0.02の関係を満足するトナー数が50％以上であるような磁性トナーとは、酸化鉄がトナー表面に局在していたり、また逆に極端に内包化されてトナー内部に偏在していたりしているような磁性トナーではなく、酸化鉄が磁性トナー中に、実質的に均一に分散されつつ、トナー粒子表面への酸化鉄の露出が抑制されている磁性トナーである。酸化鉄の分散状態が不均一であるような場合には、本願発明にかかる規定を満足することは困難である。また、酸化鉄がトナー粒子表面にほとんど露出していない磁性トナーを用いれば、帯電部材や転写部材等により磁性トナーが静電荷像担持体表面に圧接される様な画像形成方法においても、静電荷像担持体表面を削ることはほとんど無く、長期にわたり静電荷像担持体の削れやトナー融着を著しく低減させることが可能となる。
【００８２】
本発明の磁性トナーに用られる酸化鉄は、結着樹脂成分100質量部に対して、10〜200質量部用いることが好ましく、20〜180質量部用いることが更に好ましい。酸化鉄の配合量が10質量部未満では磁性トナーの着色力が乏しく、カブリの抑制も困難であり、一方、200質量部を越えると、トナー担持体への磁力による保磁力が強まり現像性が低下したり、個々のトナー粒子への酸化鉄の均一な分散が難しくなるだけでなく、定着性が低下してしまう。
【００８３】
次に、本発明のもう一つの特徴であるトナーの円形度について説明する。静電荷像担持体上の非画像部へのトナー付着や転写残余トナー量を低減するには、トナー粒子の帯電性が十分で且つ均一であることが必要である。さらに、高画質化の観点から微小粒径のトナーを用いる場合は、トナー粒子の付着力が増大するため、トナー粒子の形状も静電荷像担持体上の非画像部へのトナー付着に大きな影響を及ぼす。すなわち、トナー粒子が球形に近く、形状が揃っているほど粒子の付着面積が減少し、静電荷像担持体上の非画像部へのトナー付着や転写残余トナー量が低減され、高画質及び耐久安定性が達成される。
加えて、本発明に係るトナー粒子は帯電性が十分であり、且つ上述した如く、トナー粒子の付着力が低減されていることにより、静電荷像担持体から紙等の転写材へのトナーの転写効率も大きく改善される。これは、微小ドット画像の再現性と共に高解像性を達成するための重要なトナー性能と言える。
【００８４】
従って、このような磁性トナーを用いれば転写残トナーが非常に低減されるため、帯電部材と感光体との圧接部におけるトナーの存在量が非常に少なく、接触帯電工程を有する画像形成方法においても、感光体の削れ及びトナー融着が防止され、画像欠陥が著しく抑制されるものと考えられる。さらに、平均円形度が0.970以上のトナーは表面のエッジ部がほとんど無いため、帯電部材と感光体との圧接部において感光体表面を引っ掻くことが無いことから、感光体表面の削れが抑制されることも挙げられる。
【００８５】
これらの効果は、転写中抜けの発生しやすい接触転写工程を含む画像形成方法においても、顕著となって現れる。
本発明の磁性トナーは、更に高画質化のため、より微小な潜像ドットを忠実に現像するために、磁性トナーの重量平均粒径が3〜10μm、更には4〜8μm未満であることが好ましい。重量平均粒径が3μm未満の磁性トナーに於いては、転写効率の低下から感光体上の転写残トナーが多くなり、帯電の均一性の維持が難しくなる。さらに、磁性トナー全体の表面積が増えることに加え、粉体としての流動性及び攪拌性が低下し、個々のトナー粒子を均一に帯電させることが困難となることからカブリや転写性が悪化傾向となり、画像の不均一ムラの原因となりやすいため、本発明で使用する磁性トナーには好ましくない。また、トナーの重量平均粒径が10μmを越える場合には、文字やライン画像に飛び散りが生じやすく、高解像度が得られにくい。さらに装置が高解像度になっていくと8μm以上のトナーは１ドットの再現が悪化する傾向にある。
また、本発明に係わる磁性トナーは、示差走査熱量計により測定されるトナーのＤＳＣ曲線において、昇温時に40〜110℃、より好ましくは45〜90℃に吸熱ピークを有することが好ましい。
【００８６】
重量平均粒径が10μm以下のトナーを用いれば非常に高精細な画像を得ることができるが、粒径の小さいトナー粒子は紙等の転写材を使用した場合に紙の繊維の隙間に入り込み、熱定着用ローラからの熱の受け取りが不十分となり、低温オフセットが発生しやすい。
【００８７】
しかしながら、示差走査熱量計により測定されるトナーのＤＳＣ曲線において、昇温時に40〜110℃の範囲に吸熱ピークを有するようにトナーを設計すると、高解像性と耐オフセット性を両立させつつ感光体の削れを防止することが可能となる。より好ましくは、昇温時に45〜90℃の範囲に吸熱ピークを有することである。磁性トナーの前記吸熱ピークが40℃よりも低いと耐保存安定性や帯電性に問題が生じる場合があり、該吸熱ピークが110℃よりも高いと感光体の削れを防止することが困難となる場合がある。
【００８８】
示差走査熱量計により測定されるトナーのＤＳＣ曲線において、昇温時に吸熱ピークを40〜110℃の範囲に発現させる方法としては様々な方法があるが、例えばトナーを製造する際に、下記の従来公知のワックス成分を原材料の一部として使用することにより容易に達成可能である。
【００８９】
本発明の磁性トナーは、結着樹脂成分100質量部に対して0.5〜50質量部のワックス成分を含有することも好ましい使用形態の一つである。ワックス成分の含有量が0.5質量部未満では低温オフセット抑制効果に乏しく、50質量部を超えてしまうと長期間の保存性が低下すると共に、他のトナー材料の分散性が悪くなり、トナーの流動性の劣化や画像特性の低下につながる。
【００９０】
通常、トナー像は、転写工程で転写材上に転写され、そして、このトナー像はその後、熱・圧力等のエネルギーにより転写材上に定着され、半永久的な画像が得られる。この際の定着方法としては、熱ロール式定着が一般に良く用いられるが、上記のように、重量平均粒径が10μm以下のトナーを用いれば非常に高精細な画像を得ることができるが、粒径の小さいトナー粒子は紙等の転写材を使用した場合に紙の繊維の隙間に入り込み、熱定着用ローラからの熱の受け取りが不十分となり、低温オフセットが発生しやすい。しかしながら、本発明の磁性トナーにおいて、離型剤として適正量のワックス成分を含有させることにより、高解像性と耐オフセット性を両立させつつ感光体の削れを防止することが可能となる。
【００９１】
本発明のトナーに使用可能なワックス成分としては、パラフィンワックス、マイクロクリスタリンワックス、ペトロラクタムの如き石油系ワックス及びその誘導体、モンタンワックスびその誘導体、フィッシャートロプシュ法による炭化水素ワックス及びその誘導体、ポリエチレンに代表されるポリオレフィンワックス及びその誘導体、カルナバワックス、キャンデリラワックスの如き天然ワックス及びその誘導体などが含まれる。ここでの誘導体には酸化物や、ビニル系モノマーとのブロック共重合物、グラフト変性物が含まれる。さらに、高級脂肪族アルコール、ステアリン酸、パルミチン酸の如き脂肪酸またはその化合物、酸アミドワックス、エステルワックス、ケトン、硬化ヒマシ油及びその誘導体、植物系ワックス、動物性ワックスも使用できる。
【００９２】
これらのワックス成分の内、磁性トナーが示差走査熱量計により測定されるＤＳＣ曲線において、昇温時に40〜110℃の領域に吸熱ピークを有するためには、その範囲に最大吸熱ピークを有するワックス成分を用いることが好ましく、45〜90℃の領域に最大吸熱ピークを有するワックス成分を用いることが更に好ましい。上記の温度領域にワックス成分が最大吸熱ピークを有することにより、低温定着に大きく貢献しつつ、離型性をも効果的に発現することができる。この最大吸熱ピークが40℃未満であるとワックス成分の自己凝集力が弱くなり、結果として耐高温オフセット性が悪化する。一方、この最大吸熱ピークが110℃を越えると定着温度が高くなり低温オフセットが発生しやすくなり好ましくない。さらに、水系媒体中で造粒／重合を行い重合方法により直接トナーを得る場合、この最大吸熱ピーク温度が高いと、主に造粒中にワックス成分が析出する等の問題が生じるため好ましくない。
【００９３】
尚、トナーやワックスの吸熱ピーク温度の測定は、「ASTM D 3418-8」に準じて行う。測定には、例えばパーキンエルマー社製ＤＳＣ−７を用いる。装置検出部の温度補正はインジウムと亜鉛の融点を用い、熱量の補正についてはインジウムの融解熱を用いる。測定サンプルにはアルミニウム製のパンを用い、対照用に空パンをセットし、昇温速度１０℃／ｍｉｎで測定を行う。また、上記測定装置によって、結着樹脂成分等のガラス転移温度（Ｔｇ）を測定することもできる。
【００９４】
本発明における磁性トナーは、磁場79.6kA/m（1000エルステッド）におけるトナーの磁化の強さが10〜50Am²/kg（emu/g）であることが好ましい。現像装置内に磁気力発生手段を設けることで、磁性トナーではトナーの漏れを防止でき、トナーの搬送性或いは攪拌性を高められるばかりでなく、トナー担持体上に磁力が作用するように磁気力発生手段を設けることで、磁性トナーが穂立ちを形成するためにトナーの飛散を防止することが容易となる。しかし、トナーの磁場79.6kA/mにおける磁化の強さが10Am²/kg未満であると、上記の効果が得られず、トナー担持体上に磁力を作用させるとトナーの穂立ちが不安定となり、トナーへの帯電付与が均一に行えないことによるカブリ、画像濃度ムラ、転写残トナーの回収不良等の画像不良を生じ易くなる。
【００９５】
トナーの磁場79.6kA/mにおける磁化の強さが50Am²/kgよりも大きいと、トナーに磁力を作用させると磁気凝集によりトナーの流動性が著しく低下し、帯電性の低下に伴うカブリ及び画像汚れを生じ易くなる。尚、磁化の強さは使用する上記酸化鉄の含有量を調節することにより、上記の範囲とすることができる。
また、本発明のトナーのように0.970以上の円形度を有することによって、トナー担持体上でのトナーの穂立ちが細く密になることによって、帯電が均一化され更にかぶりが大幅に減少する。
本発明において磁性トナーの磁化の強さは、振動型磁力計ＶＳＭ Ｐ−１−１０（東英工業社製）を用いて、25℃の室温にて外部磁場79.6kA/mで測定する。また、上述の酸化鉄の磁気特性は、25℃の室温にて外部磁場796kA/mで測定する。
【００９６】
本発明の磁性トナーは、磁性トナーのＴＨＦ可溶分のゲルパーミエーションクロマトグラフィー（ＧＰＣ）により測定した分子量分布において、分子量5000〜50000の範囲にメインピークのピークトップがあることが良く、より好ましくは8000〜40000の範囲である。ピークトップが5000未満であると、トナー粒子を重合によって製造する場合、重合中の液滴の粘度上昇が非常に小さく、疎水化処理酸化鉄がトナー粒子の表面近傍に偏在しやすくなる傾向があり、（Ｂ／Ａ）を0.001未満とすることが困難となる場合がある。また、トナーの耐保存安定性に問題が生じたり、多数枚のプリントアウトを行った際にトナーの劣化が著しくなる。逆に、ピークトップが50000を超える場合には、低温定着性に問題が生じるとともに、トナー粒子を重合によって製造する場合、重合中の液滴粘度の急激な上昇により疎水化処理酸化鉄の分散性が悪化する傾向がある。また、円形度を0.970以上とすることが困難になってくる。
【００９７】
分子量5000〜50000の範囲にピークトップを有するメインピークは、下記式（１）により算出されるＸが1.4以下であることが良く、特に好ましくは分子量8000〜40000の範囲にピークトップを有するメインピークを有し、Ｘが1.1以下である。
【００９８】
【数４】

尚、分子量10000および100000の溶出時間（sec）とは、後述する標準ポリスチレンにより検量線を作製し、その検量線の数式の分子量の項に10000および100000を入力して算出される計算上の溶出時間のことである。
【００９９】
粉砕法トナーにおいて、不溶分（架橋成分）を含有する結着樹脂成分を混練することにより、耐高温オフセット性に効果がある高分子量成分を生成させるという方法がとられる場合が従来よりあるが、前述したように分子鎖が混練により切断されて生成した高分子は自ずと分子量分布が広いものとなり、耐高温オフセット性にあまり寄与せず、低温定着性を阻害してしまう中間分子量成分が多量に生成してしまったり、混練時の過度の切断により超低分子量成分が生じてしまい、感光体やスリーブなどへのトナーの融着が問題となる場合がある。また、従来の重合法トナーの場合には、架橋剤の存在下で着色剤、単量体などからなる組成物を重合させることによってＴＨＦ不溶分を生成させることは可能ではあるが、溶液重合法とは異なり懸濁重合法は本質的に生成する結着樹脂成分の分子量分布が広くなってしまうため、ＴＨＦに可溶な成分の分子量分布をシャープにすることは従来の技術では困難である。
【０１００】
本発明者らは適度の量のＴＨＦ不溶分を生成させつつ、ＴＨＦ可溶分の分子量分布を如何にシャープにするかについて鋭意検討を行った結果、特定の重合条件下において、特定の原材料を組み合わせることによって、耐高温オフセット性に効果的な不溶分を生成させ、かつ、前記Ｘを1.4以下に収め、メインピークのピークトップを所定の分子量範囲に収めることで、耐高温オフセット性を維持しつつ、低温定着性にも優れ、さらに帯電の均一性が極めて良好となることを見出した。
【０１０１】
尚、前記Ｘの値が1.4以下に入ってさえいれば、メインピークは高分子量側、低分子量側に多少裾引きしていても本発明の効果に悪影響はないが、ＧＰＣより測定した分子量分布における結着樹脂成分の可溶成分の全面積に対して分子量30万以上の成分は20面積％未満、より好ましくは10面積％未満、分子量2000〜5000の成分は15面積％未満、より好ましくは10面積％未満であると本発明の効果が一層発揮される。
【０１０２】
本発明の磁性トナーを得るために好適に利用される製造方法は後述するが、例えば重合法による場合には、高度に表面処理された酸化鉄、ワックス成分、架橋剤、α-メチルスチレンダイマーなどの連鎖移動剤を含有する単量体組成物を水系媒体中で造粒し、重合開始剤として有機系過酸化物を用いて懸濁重合することにより容易に得ることができる。
【０１０３】
尚、ＧＰＣによるＴＨＦに可溶な結着樹脂成分に由来する成分の分子量の測定は、以下の様にして行えばよい。
【０１０４】
トナーをＴＨＦに室温で２４時間静置して溶解した溶液を、ポア径が0.2μｍの耐溶剤性メンブランフィルターで濾過してサンプル溶液とし、以下の条件で測定する。尚、サンプル調製は、ＴＨＦに可溶な成分の濃度が0.4〜0.6質量％になるようにＴＨＦの量を調整する。
【０１０５】
装置 ： 高速GPC HLC8120 GPC（東ソー社製）
カラム： Shodex KF-801、802、803、804、805、806、807の７連（昭和電工社製）
溶離液： ＴＨＦ
流速 ： 1.0ml/min
オーブン温度： 40.0℃
試料注入量 ： 0.10ml
また、試料の分子量の算出にあたっては、標準ポリスチレン樹脂（東ソー社製ＴＳＫ スタンダード ポリスチレンF-850、F-450、F-288、F-128、F-80、F-40、F-20、F-10、F-4、F-2、F-1、A-5000、A-2500、A-1000、A-500）により作成した分子量校正曲線を使用する。
【０１０６】
また、本発明の磁性トナーはＴＨＦ不溶分（結着樹脂の架橋成分）を適度に含有していることが好ましく、その量はＴＨＦ可溶成分の分子量分布、特に高分子量成分の割合がどのくらい存在しているかにより異なるが、結着樹脂成分を基準として通常1〜60質量％、好ましくは5〜40質量％の範囲である。尚、ＴＨＦ不溶分の測定は以下の様にして行う。
【０１０７】
トナー粒子又はトナー1gを精秤して円筒ろ紙に仕込み、ＴＨＦ200mlにて２０時間ソックスレー抽出する。その後円筒ろ紙を取り出し、40℃で２０時間真空乾燥して残渣重量を測定することにより、算出する。この際、トナーの中には酸化鉄、電荷制御剤、ワックス成分、外添剤等の、結着樹脂成分以外の成分を含有するため、これらの含有量とこれらがＴＨＦにて可溶か不溶かを考慮して結着樹脂成分を基準としたＴＨＦ不溶分を算出する。結着樹脂成分以外のトナーの構成成分でＴＨＦに可溶な成分（例えば、ＴＨＦに可溶なワックス等）が使用されている場合には、その成分の含有量を別途分析により算出して、結着樹脂成分のうちのどれだけがＴＨＦに不溶化しているのかに換算する。
【０１０８】
本発明の磁性トナーの構成材料である結着樹脂成分は、分子量分布の制御が比較的容易であることから、スチレン系樹脂を主体としていることが好ましい。該スチレン系樹脂は重合開始剤を用いて、スチレンを含む単量体を重合させて得られたものである。即ち、スチレン単量体と他の重合性単量体を共重合することにより得ることができる。
【０１０９】
使用できる他の重合性単量体としては特に制限はないが、一例を挙げれば、ｏ−メチルスチレン、ｍ−メチルスチレン、ｐ−メチルスチレン、ｐ−メトキシスチレン、ｐ−エチルスチレン等のスチレン系単量体；アクリル酸メチル、アクリル酸エチル、アクリル酸ｎ−ブチル、アクリル酸イソブチル、アクリル酸ｎ−プロピル、アクリル酸ｎ−オクチル、アクリル酸ドデシル、アクリル酸２−エチルヘキシル、アクリル酸ステアリル、アクリル酸２−クロルエチル、アクリル酸フェニル等のアクリル酸エステル類；メタクリル酸メチル、メタクリル酸エチル、メタクリル酸ｎ−プロピル、メタクリル酸ｎ−ブチル、メタクリル酸イソブチル、メタクリル酸ｎ−オクチル、メタクリル酸ドデシル、メタクリル酸２−エチルヘキシル、メタクリル酸ステアリル、メタクリル酸フェニル、メタクリル酸ジメチルアミノエチル、メタクリル酸ジエチルアミノエチル等のメタクリル酸エステル類；その他のアクリロニトリル、メタクリロニトリル、アクリルアミド等の単量体が挙げられる。これらは単独、または一般的には出版物ポリマーハンドブック第２版III-p139〜192（John Wiley&Sons社製）に記載の理論ガラス転移温度（Ｔｇ）が、40〜70℃を示す樹脂となるように単量体を適宜混合して用いられる。理論ガラス転移温度が40℃未満の場合にはトナーの保存安定性や耐久安定性の面から問題が生じやすく、一方70℃を超える場合にはトナーの定着性に問題が生じる場合がある。
【０１１０】
本発明で使用される重合開始剤としては、従来公知のアゾ系重合開始剤、有機過酸化物系重合開始剤などがあり、アゾ系重合開始剤としては、２，２'−アゾビス−（２，４−ジメチルバレロニトリル）、２，２'−アゾビスイソブチロニトリル、１，１'−アゾビス（シクロヘキサン−１−カルボニトリル）、２，２'−アゾビス−４−メトキシ−２，４−ジメチルバレロニトリル、アゾビスイソブチロニトリル等が例示され、有機過酸化物系重合開始剤としてはｔ−ブチルパーオキシアセテート、ｔ−ブチルパーオキシラウレート、ｔ−ブチルパーオキシピバレート、ｔ−ブチルパーオキシ−２−エチルヘキサノエート、ｔ−ブチルパーオキシイソブチレート、ｔ−ブチルパーオキシネオデカノエート、ｔ−ヘキシルパーオキシアセテート、ｔ−ヘキシルパーオキシラウレート、ｔ−ヘキシルパーオキシピバレート、ｔ−ヘキシルパーオキシ−２−エチルヘキサノエート、ｔ−ヘキシルパーオキシイソブチレート、ｔ−ヘキシルパーオキシネオデカノエート、ｔ−ブチルパーオキシベンゾエート、α，α'−ビス（ネオデカノイルパーオキシ）ジイソプロピルベンゼン、クミルパーオキシネオデカノエート、１，１，３，３−テトラメチルブチルパーオキシ−２−エチルヘキサノエート、１，１，３，３−テトラメチルブチルパーオキシネオデカノエート、１−シクロヘキシル−１−メチルエチルパーオキシネオデカノエート、２，５−ジメチル−２，５−ビス（２−エチルヘキサノイルパーオキシ）ヘキサン、１−シクロヘキシル−１−メチルエチルパーオキシ−２−エチルヘキサノエート、ｔ−ヘキシルパーオキシイソプロピルモノカーボネート、ｔ−ブチルパーオキシイソプロピルモノカーボネート、ｔ−ブチルパーオキシ２−エチルヘキシルモノカーボネート、ｔ−ヘキシルパーオキシベンゾエート、２，５−ジメチル−２，５−ビス（ベンゾイルパーオキシ）ヘキサン、ｔ−ブチルパーオキシ−ｍ−トルオイルベンゾエート、ビス（ｔ−ブチルパーオキシ）イソフタレート、ｔ−ブチルパーオキシマレイックアシッド、ｔ−ブチルパーオキシ−３，５，５−トリメチルヘキサノエート、２，５−ジメチル−２，５−ビス（ｍ−トルオイルパーオキシ）ヘキサンなどのパーオキシエステル；ベンゾイルパーオキサイド、ラウロイルパーオキサイド、イソブチリルパーオキサイドなどのジアシルパーオキサイド；ジイソプロピルパーオキシジカーボネート、 ビス（４−ｔ−ブチルシクロヘキシル）パーオキシジカーボネートなどのパーオキシジカーボネート、１，１−ジ−ｔ−ブチルパーオキシシクロヘキサン、１，１−ジ−ｔ−ヘキシルパーオキシシクロヘキサン、１，１−ジ−ｔ−ブチルパーオキシ−３，３，５−トリメチルシクロヘキサン、２，２−ジ−ｔ−ブチルパーオキシブタンなどのパーオキシケタール；ジ−ｔ−ブチルパーオキサイド、ジクミルパーオキサイド、ｔ−ブチルクミルパーオキサイドなどのジアルキルパーオキサイド；その他としてｔ−ブチルパーオキシアリルモノカーボネート等が挙げられ、必要に応じてこれらの開始剤を２種以上用いることもできる。
【０１１１】
上記した重合開始剤の中で特に有機過酸化物系重合開始剤は、水素引き抜き（架橋）反応を重合反応とともに起こすため、ＴＨＦ不溶分を適度に生成し、かつ、中間分子量成分を少なくできる傾向が強く、本発明のトナーが得られやすいので好ましく用いられる。また、これら有機過酸化物系重合開始剤の中でも、パーオキシエステル、パーオキシジカーボネート、ジアシルパーオキサイドが好適に利用され、この中でジアシルパーオキサイドを用いるとＴＨＦ可溶分のメインピークが特にシャープとなるため、より均一帯電性が向上するため好ましい。
【０１１２】
本発明で使用される重合開始剤は、単量体100質量部に対し0.2〜20質量部を用いることが好ましく、該添加量で重合反応を行なうと、分子量5000〜50000の間にメインピークを有する重合体が得られ、トナーに望ましい強度と適当な溶融特性を与えることが出来る。
【０１１３】
また、本発明で有機過酸化物系重合開始剤を用いる場合には、その理論活性酸素量は3.0〜12.0％の範囲にあることが望ましく、3.0％よりも小さいと重合開始剤を多量に使用しなければならない傾向があって経済的に不利であり、12.0％を超えると取り扱いおよび重合反応の制御が困難となる場合がある。
【０１１４】
本発明においては、ＴＨＦ不溶分量の制御とＴＨＦに可溶な結着樹脂成分のメインピークをシャープにするため、従来公知の連鎖移動剤を単量体組成物に添加してラジカル重合を行うことが好ましい。
【０１１５】
この際使用できる連鎖移動剤としては、例えば、α-メチルスチレンダイマー、ｔ−ドデシルメルカプタン、ｎ−ドデシルメルカプタン、ｎ−オクチルメルカプタン、四塩化炭素、四臭化炭素などを挙げることができる。これらの中でより好ましく用いられる連鎖移動剤は、α-メチルスチレンダイマー、ｔ−ドデシルメルカプタン、ｎ−ドデシルメルカプタンである。α-メチルスチレンダイマーはｔ−ドデシルメルカプタンなどのチオール類よりも前記Ｘの値を小さくすることが可能であり、特に好ましく用いられる。これらの連鎖移動剤は、重合開始前、あるいは重合途中に添加することができる。これらの連鎖移動剤は、単量体100質量部に対して、通常、0.01〜10質量部、好ましくは0.1〜5質量部の割合で用いられる。
【０１１６】
本発明に係わる重合トナーを製造する際は、ＴＨＦに可溶な結着樹脂成分の分子量分布の制御やＴＨＦ不溶分の含有量の調節のために単量体組成物に架橋剤を添加することが好ましく、好ましい添加量としては単量体に対して0.001〜15質量％である。
【０１１７】
ここで架橋剤としては、重合可能な二重結合を１分子中に２個以上有する化合物であれば特に制限されないが、例えば、ジビニルベンゼン、ジビニルナフタレン、エチレングリコールジアクリレート、エチレングリコールジメタクリレート、１，３−ブタンジオールジメタクリレート、トリメチロールプロパントリアクリレート、トリメチロールプロパントリメタクリレート、ペンタエリスリトールテトラアクリレート、ジアリルエーテル、ペンタエリスリトールトリアクリレート、トリアリルエーテル、ジビニルアニリン、ジビニルエーテル、ジビニルスルフィド、ジビニルスルホン等の重合可能な二重結合を複数個有する低分子架橋剤、不飽和ポリエステル、スチレン−ブタジエン共重合体等の架橋性重合体が挙げられ、これらは単独もしくは混合して用いられる。
【０１１８】
本発明のトナーは、粉砕法によって製造することも可能であるが、粉砕法ではトナーの平均円形度を0.970以上とするために機械的、熱的あるいは何らかの特殊な処理を行うことが必要となることから、懸濁重合法により製造することが好ましい。通常の磁性体を用いて懸濁重合によりトナーを製造したとしても、磁性体が分散性に劣るために磁性体がトナー表面に偏在してしまったり、水系媒体中における造粒時に磁性体が乱雑に動き、それに引きずられて粒子形状がゆがんだりするために、平均円形度が0.970以上のトナーは得られがたいものであったが、本発明において用いられる酸化鉄は、高いレベルでの均一な疎水化が行われているため、平均円形度が0.970以上のトナーを容易に得ることができる。
【０１１９】
本発明では、単量体組成物に樹脂を添加して重合しても良い。例えば、単量体では水溶性のため水性懸濁液中では溶解して乳化重合を起こすため使用できないアミノ基、カルボン酸基、水酸基、スルフォン酸基、グリシジル基、ニトリル基等の親水性官能基含有の単量体成分をトナー中に導入したい時には、これらとスチレンあるいはエチレン等のビニル化合物とのランダム共重合体、ブロック共重合体、あるいはグラフト共重合体等の共重合体の形にして、あるいはポリエステル、ポリアミド等の重縮合体、ポリエーテル、ポリイミン等の重付加重合体の形で使用が可能となる。
【０１２０】
こうした極性官能基を含む高分子重合体をトナー中に共存させると、前述のワックス成分を相分離させ、より内包化が強力となり、耐オフセット性、耐ブロッキング性、低温定着性の良好なトナーを得ることができる。
上記樹脂の使用量としては、重合性単量体100質量部に対して1〜20質量部が好ましい。使用量が1質量部未満では添加効果が小さく、一方20質量部を超えて使用された場合には、重合トナーの種々の物性設計が難しくなってしまう。またこれら極性官能基を含む高分子重合体の平均分子量は3000以上が好ましく用いられる。分子量3000未満、特に2000以下では、本重合体が表面付近に集中し易いことから、現像性、耐ブロッキング性等に悪い影響が起こり易くなり好ましくない。また、単量体を重合して得られるトナーの分子量範囲とは異なる分子量の重合体を単量体中に溶解して重合すれば、分子量分布の広い、耐オフセット性の高いトナーを得ることができる。
【０１２１】
本発明のトナーには、荷電特性を安定化するために荷電制御剤を配合しても良い。荷電制御剤としては、公知のものが利用できるが、特に帯電スピードが速く、且つ、一定の帯電量を安定して維持できる荷電制御剤が好ましい。
さらに、トナーを直接重合法を用いて製造する場合には、重合阻害性が低く、水系分散媒体への可溶化物が実質的にない荷電制御剤が特に好ましい。具体的な化合物としては、ネガ系荷電制御剤としてサリチル酸、アルキルサリチル酸、ジアルキルサリチル酸、ナフトエ酸、ダイカルボン酸等の芳香族カルボン酸の金属化合物、アゾ染料もしくはアゾ顔料の金属塩または金属錯体、スルホン酸又はカルボン酸基を側鎖に持つ高分子型化合物、ホウ素化合物、尿素化合物、ケイ素化合物、カリックスアレーン等が挙げられる。ポジ系荷電制御剤として四級アンモニウム塩、その四級アンモニウム塩を側鎖に有する高分子型化合物、グアニジン化合物、ニグロシン系化合物、イミダゾール化合物等が挙げられる。
【０１２２】
これらの荷電制御剤は、重合性単量体100質量部に対して0.5〜10質量部使用することが好ましい。しかしながら、本発明の磁性トナーは、荷電制御剤の添加は必須ではなく、磁性トナーの層圧規制部材やトナー担持体との摩擦帯電を積極的に利用することでトナー中に必ずしも荷電制御剤を含む必要はない。
【０１２３】
さらにまた、酸化鉄以外に他の着色剤を併用しても良い。併用し得る着色材料としては、磁性あるいは非磁性無機化合物、公知の染料及び顔料が挙げられる。具体的には、例えば、コバルト、ニッケルの如き強磁性金属粒子、またはこれらにクロム、マンガン、銅、亜鉛、アルミニウム、希土類元素を加えた合金、ヘマタイト、チタンブラック、ニグロシン染料／顔料、カーボンブラック、フタロシアニンが挙げられる。これらもまた、酸化鉄と同様に表面を疎水化処理して用いても良い。
【０１２４】
懸濁重合法による磁性トナーの製造では、一般に上述のトナー組成物、すなわち重合性単量体中に、酸化鉄、着色剤、離型剤、可塑剤、結着樹脂、荷電制御剤、架橋剤、連鎖移動剤等トナーとして必要な成分及びその他の添加剤、例えば重合反応で生成する重合体の粘度を低下させるために入れる有機溶媒、分散剤等を適宜加えて、ホモジナイザー、ボールミル、コロイドミル、超音波分散機等の分散機によって均一に溶解または分散させた単量体組成物を、分散安定剤を含有する水系媒体中に懸濁する。
【０１２５】
この時、高速撹拌機もしくは超音波分散機のような高速分散機を使用して一気に所望のトナー粒子のサイズとするほうが、得られるトナー粒子の粒径がシャープになる。重合開始剤添加の時期としては、重合性単量体中に他の添加剤を添加する時同時に加えても良いし、水系媒体中に懸濁する直前に混合しても良い。また、造粒直後、重合反応を開始する前に重合性単量体あるいは溶媒に溶解した重合開始剤を加えることもできる。
【０１２６】
造粒後は、通常の撹拌機を用いて、粒子状態が維持され且つトナー粒子の浮遊・沈降が防止される程度の撹拌を行なえば良い。
【０１２７】
本発明の懸濁重合法においては、分散安定剤として公知の界面活性剤や有機・無機分散剤が使用でき、中でも無機分散剤が画像欠陥の原因となる超微粉を生じ難く、その立体障害性により分散安定性を得ているので反応温度を変化させても安定性が崩れ難く、洗浄も容易でトナーに悪影響を与え難いので、好ましく使用できる。こうした無機分散剤の例としては、燐酸カルシウム、燐酸マグネシウム、燐酸アルミニウム、燐酸亜鉛等の燐酸多価金属塩；炭酸カルシウム、炭酸マグネシウム等の炭酸塩；メタ硅酸カルシウム、硫酸カルシウム、硫酸バリウム等の無機塩；水酸化カルシウム、水酸化マグネシウム、水酸化アルミニウム、シリカ、ベントナイト、アルミナ等の無機酸化物が挙げられる。これらの無機分散剤は、重合性単量体100質量部に対して、0.2〜20質量部を単独でまたは２種類以上組み合わせて使用することが好ましい。重量平均粒径が5μm以下のトナーとしたい場合など、より微粒化されたトナーを目的とする場合には、0.001〜0.1質量部の界面活性剤を併用しても良い。
【０１２８】
界面活性剤としては、例えばドデシルベンゼン硫酸ナトリウム、テトラデシル硫酸ナトリウム、ペンタデシル硫酸ナトリウム、オクチル硫酸ナトリウム、オレイン酸ナトリウム、ラウリル酸ナトリウム、ステアリン酸ナトリウム、ステアリン酸カリウムが挙げられる。
【０１２９】
これら無機分散剤を用いる場合には、そのまま使用しても良いが、より細かい粒子を得るため、水系媒体中にて該無機分散剤粒子を生成させることができる。例えば、燐酸カルシウムの場合、高速撹拌下、燐酸ナトリウム水溶液と塩化カルシウム水溶液とを混合して、水不溶性の燐酸カルシウムを生成させることができ、より均一で細かな分散が可能となる。
この時、同時に水溶性の塩化ナトリウム塩が副生するが、水系媒体中に水溶性塩が存在すると、重合性単量体の水への溶解が抑制されて、乳化重合に依る超微粒トナーが発生し難くなるので、より好都合である。重合反応終期に残存重合性単量体を除去する時には障害となることから、水系媒体を交換するか、イオン交換樹脂で脱塩したほうが良い。無機分散剤は、重合終了後酸あるいはアルカリで溶解して、ほぼ完全に取り除くことができる。
【０１３０】
前記重合工程においては、重合温度は40℃以上、一般には50〜90℃の温度に設定して重合を行なう。この温度範囲で重合を行なうと、内部に封じられるべきワックス成分等が、相分離により析出して内包化がより完全となる。
残存する重合性単量体を消費するために、重合反応終期ならば、反応温度を90〜150℃にまで上げることは可能である。
【０１３１】
また、本発明のトナーは、無機微粉体をトナー粒子表面に有する。無機微粉体を本発明のトナー粒子表面に存在させることで、トナーの流動性を向上させるだけでなく、帯電性もさらに安定とすることができる。無機微粉体としては例えば、シリカ微粉体、酸化チタン微粉体、アルミナ微粉体など、またはこれらの複合酸化物があげられ、これらは必要に応じて疎水化処理したものを用いる。これらの中で、シリカ微粉体、特に疎水化処理されたシリカ微粉体を用いることが好ましい。
【０１３２】
本発明の磁性トナーに用いられる無機微粉体は、個数一次平均粒径が4〜80nm、ＢＥＴ法で測定した窒素吸着による比表面積が30m²/g以上のもの、特に50〜400m²/gの範囲のものが良好な結果を与えることができるため好ましい。比表面積の測定は酸化鉄と同様に行う。
【０１３３】
本発明において、無機微粉体の個数一次平均粒径の測定法は、走査型電子顕微鏡により拡大撮影したトナーの写真で、更に走査型電子顕微鏡に付属させたＸＭＡ等の元素分析手段によって無機微粉体の含有する元素でマッピングされたトナーの写真を対照しつつ、トナー表面に付着或いは遊離して存在している無機微粉体の１次粒子を１００個以上測定し、個数一次平均粒径を求めることが出来る。
【０１３４】
本発明に用いられるシリカ微粉体はケイ素ハロゲン化合物の蒸気相酸化により生成されたいわゆる乾式法またはヒュームドシリカと称される乾式シリカ及び水ガラス等から製造されるいわゆる湿式シリカの両方が使用可能であるが、表面及び内部にあるシラノール基が少なく、製造残渣のない乾式シリカが好ましく用いられる。
さらに本発明に用いるシリカ微粉体は疎水化処理されているものが好ましい。
【０１３５】
疎水化処理に使用されるシランカップリング剤としては、例えばヘキサメチルジシラザン、トリメチルシラン、トリメチルクロルシラン、トリメチルエトキシシラン、ジメチルジクロルシラン、メチルトリクロルシラン、アリルジメチルクロルシラン、アリルフェニルジクロルシラン、ベンジルジメチルクロルシラン、ブロムメチルジメチルクロルシラン、α−クロルエチルトリクロルシラン、β−クロルエチルトリクロルシラン、クロルメチルジメチルクロルシラン、トリオルガノシランメルカプタン、トリメチルシリルメルカプタン、トリオルガノシリルアクリレート、ビニルジメチルアセトキシシラン、ジメチルエトキシシラン、ジメチルジメトキシシラン、ジフェニルジエトキシシラン、ヘキサメチルジシロキサン、１，３−ジビニルテトラメチルジシロキサン、１，３−ジフェニルテトラメチルジシロキサン等が挙げられる。有機ケイ素化合物としては、シリコーンオイルが挙げられる。
【０１３６】
好ましいシリコーンオイルとしては、25℃における粘度がおよそ30〜1,000mm²/s（cSt）のものが用いられ、例えばジメチルシリコーンオイル、メチルフェニルシリコーンオイル、α−メチルスチレン変性シリコーンオイル、クロルフェニルシリコーンオイル、フッ素変性シリコーンオイルが好ましい。
【０１３７】
シリコーンオイル処理の方法は、例えばシランカップリング剤で処理されたシリカ微粉体とシリコーンオイルとをヘンシェルミキサー等の混合機を用いて直接混合しても良いし、ベースとなるシリカへシリコーンオイルを噴射する方法によっても良い。あるいは適当な溶剤にシリコーンオイルを溶解あるいは分散させた後、ベースのシリカ微粉体とを混合し、溶剤を除去して作製しても良い。
【０１３８】
本発明の磁性トナーには、必要に応じて流動性向上剤以外の外部添加剤を添加してもよい。
【０１３９】
例えば、クリーニング性を向上させる等の目的で、一次粒径が30nmを超える（好ましくはＢＥＴ比表面積が50m²/g未満）微粒子、より好ましくは一次粒径が50nm以上（好ましくはＢＥＴ比表面積が30m²/g未満）で球状に近い無機微粒子または有機微粒子をさらに添加することも好ましい形態の一つである。例えば球状のシリカ粒子、球状のポリメチルシルセスキオキサン粒子、球状の樹脂粒子を用いるのが好ましい。
【０１４０】
更に他の添加剤、例えばテフロン粉末、ステアリン酸亜鉛粉末、ポリフッ化ビニリデン粉末等の滑剤粉末；酸化セリウム粉末、炭化硅素粉末、チタン酸ストロンチウム粉末等の研磨剤；ケーキング防止剤；カーボンブラック粉末、酸化亜鉛粉末、酸化スズ粉末等の導電性付与剤；逆極性の有機微粒子、無機微粒子の現像性向上剤等を少量加えることもできる。これらの添加剤も、その表面を疎水化処理して用いることが好ましい。
【０１４１】
上述の添加剤は、磁性トナー100質量部に対して0.1〜5質量部（好ましくは0.1〜3質量部）使用するのが良い。
【０１４２】
本発明のトナーを粉砕法により製造する場合は、公知の方法を用いることができる。公知の方法としては、例えば、後述の結着樹脂、上記酸化鉄、ワックス成分、荷電制御剤、場合によっては着色剤等のトナーとして必要な成分及びその他の添加剤等をヘンシェルミキサー、ボールミル等の混合器中で十分混合した後、加熱ロール、ニーダー、エクストルーダーのような熱混練機を用いて熔融混練して、樹脂類をお互いに相熔させた中に酸化鉄等の他のトナー材料を分散又は溶解させ、冷却固化、粉砕後に、分級、必要に応じて表面処理を行なってトナー粒子を得、必要に応じて無機微粉体等を添加して混合することによって磁性トナーを得ることが出来る。分級及び表面処理の順序はどちらが先でもよい。分級工程においては生産効率の点からは、多分割分級機を用いることが好ましい。
粉砕工程は、機械衝撃式、ジェット式等の公知の粉砕装置を用いて行うことができる。本発明に係わる特定の円形度を有する磁性トナーを得るためには、さらに熱をかけて粉砕したり、または補助的に機械的衝撃を加える処理をすることが好ましい。また、微粉砕（必要に応じて分級）されたトナー粒子を熱水中に分散させる湯浴法、熱気流中を通過させる方法などを用いてもよい。
【０１４３】
機械的衝撃力を加える方法としては、例えば川崎重工社製のクリプトロンシステムやターボ工業社製のターボミル等の機械衝撃式粉砕機を用いる方法がある。また、ホソカワミクロン社製のメカノフージョンシステムや奈良機械製作所製のハイブリダイゼーションシステム等の装置のように、高速回転する羽根によりトナーをケーシングの内側に遠心力により押しつけ、圧縮力、摩擦力等の力によりトナーに機械的衝撃力を加える方法を用いてもよい。
【０１４４】
機械的衝撃を加える処理をする場合には、処理時の雰囲気温度をトナーのガラス転移点Ｔｇ付近の温度（すなわち、ガラス転移点Ｔｇの±30℃の範囲の温度）とすることが、凝集防止と生産性の観点から好ましい。さらに好ましくは、トナーのガラス転移点Ｔｇの±20℃の範囲の温度で処理を行うことが、転写効率を向上させるのに特に有効である。
【０１４５】
さらにまた、本発明のトナーは、特公昭56-13945号公報等に記載のディスク又は多流体ノズルを用いて溶融混合物を空気中に霧化し球状トナーを得る方法や、単量体には可溶で得られる重合体が不溶な水系有機溶剤を用いて直接トナーを生成する分散重合方法、又は水溶性の極性重合開始剤の存在下で直接重合させてトナーを生成するソープフリー重合方法に代表される乳化重合方法等を用いてトナーを製造する方法でも製造が可能である。
【０１４６】
本発明のトナーを粉砕法により製造する場合の結着樹脂としては、ポリスチレン、ポリビニルトルエン等のスチレン及びその置換体の単重合体；スチレン−プロピレン共重合体、スチレン−ビニルトルエン共重合体、スチレン−ビニルナフタリン共重合体、スチレン−アクリル酸メチル共重合体、スチレン−アクリル酸エチル共重合体、スチレン−アクリル酸ブチル共重合体、スチレン−アクリル酸オクチル共重合体、スチレン−アクリル酸ジメチルアミノエチル共重合体、スチレン−メタアクリル酸メチル共重合体、スチレン−メタアクリル酸エチル共重合体、スチレン−メタアクリル酸ブチル共重合体、スチレン−メタクリル酸ジメチルアミノエチル共重合体、スチレン−ビニルメチルエーテル共重合体、スチレン−ビニルエチルエーテル共重合体、スチレン−ビニルメチルケトン共重合体、スチレン−ブタジエン共重合体、スチレン−イソプレン共重合体、スチレン−マレイン酸共重合体、スチレン−マレイン酸エステル共重合体等のスチレン系共重合体；ポリメチルメタクリレート、ポリブチルメタクリレート、ポリ酢酸ビニル、ポリエチレン、ポリプロピレン、ポリビニルブチラール、シリコン樹脂、ポリエステル樹脂、ポリアミド樹脂、エポキシ樹脂、ポリアクリル酸樹脂、ロジン、変性ロジン、テンペル樹脂、フェノール樹脂、脂肪族または脂環族炭化水素樹脂、芳香族系石油樹脂、パラフィンワックス、カルナバワックス等を単独または混合して使用できる。特に、スチレン系共重合体及びポリエステル樹脂が現像特性、定着性等の点で好ましい。
＜２＞本発明の磁性トナーを用いた画像形成方法
本発明の画像形成方法は、帯電工程、静電潜像形成工程、現像工程、転写工程とを有し、トナーとして本発明の磁性トナーを用いたものである。
【０１４７】
以下に、本発明の画像形成方法の実施形態を図に沿って詳細に説明するが、本発明はこれらに限定されない。
図１において、像担持体としての感光ドラム１００の周囲に、接触帯電部材である帯電ローラ１１７、現像手段である現像器１４０、転写手段である転写ローラ１１４、クリーナ１１６、レジスタローラ１２４等が設けられている。そして感光ドラム１００は、帯電ローラ１１７によって−７００Ｖに帯電される。（印加電圧は交流電圧-2.0kVpp（Vpp：ピーク間電位）、直流電圧-700Vdc）そして、レーザー発生装置１２１によりレーザー光１２３を感光ドラム１００に照射する事によって露光される。感光ドラム１００上の静電潜像は現像器１４０によって一成分磁性トナーで現像され、転写材を介して感光ドラムに当接された転写ローラ１１４により転写材上へ転写される。トナー像をのせた転写材Ｐは、搬送ベルト１２５等により定着装置１２６へ運ばれ転写材Ｐ上に定着される。
また、一部感光ドラム上に残されたトナーはクリーニング手段であるクリーナ１１６によりクリーニングされる。現像器１４０は、図２に示すように感光ドラム１００に近接して、アルミニウム、ステンレス等非磁性金属で作られた円筒状のトナー担持体１０２（以下、「現像スリーブ」ともいう）が配設され、感光ドラム１００と現像スリーブ１０２との間隙は、図示されないスリーブ／感光体間隙保持部材等により約300μmに維持されている。この間隙は、必要により替えることは可能である。現像スリーブ１０２内にはマグネットローラ１０４が、現像スリーブ１０２と同心的に固定、配設されている。但し、現像スリーブ１０２は回転可能である。マグネットローラ１０４には図示の如く複数の磁極が具備されており、Ｓ１は現像、Ｎ１はトナーコート量規制、Ｓ２はトナーの取り込み／搬送、Ｎ２はトナーの吹き出し防止に影響している。
【０１４８】
トナーは現像スリーブ１０２に塗布され、付着して搬送される。搬送される磁性トナー量を規制するトナー層厚規制部材として、弾性ブレード１０３が配設され、弾性ブレード１０３の現像スリーブ１０２に対する当接圧により現像領域に搬送されるトナー量が制御される。現像領域では、感光ドラム１００と現像スリーブ１０２との間に直流電圧及び交流電圧の現像バイアスが印加され、現像スリーブ１０２上トナーは静電潜像に応じて感光ドラム１００上に飛翔し可視像となる。
【０１４９】
本発明のトナーを使用した現像方法の一例として、トナー担持体と静電荷像担持体とが非接触である系について説明する。
【０１５０】
非接触の現像方法においては、トナー担持体上にトナー担持体−感光体（静電荷像担持体）の最近接距離（Ｓ−Ｄ間）よりも薄い厚さで、磁性トナーが塗布され、交番電界を印加して現像を行う。すなわち、トナー担持体上の磁性トナーを規制する層厚規制部材によって、感光体とトナー担持体の最近接間隙よりも、トナー担持体上のトナー層厚が小さくなるように設定される。この際に、トナー担持体上の磁性トナーを規制する層厚規制部材が弾性部材であり、トナーを介してトナー担持体に当接されていることが磁性トナーを均一帯電させる観点から特に好ましい。
【０１５１】
また、トナー担持体は感光体に対して100〜1000μmの離間距離を有して対向して設置されることが好ましく、120〜500μmの離間距離を有して対向して設置されることが更に好ましい。トナー担持体の感光体に対する離間距離が100μmよりも小さいと、離間距離の振れに対するトナーの現像特性の変化が大きくなるため、安定した画像性を満足する画像形成装置を量産することが困難となる。トナー担持体の感光体に対する離間距離が1000μmよりも大きいと、現像装置への転写残トナーの回収性が低下し、回収不良によるカブリを生じ易くなる。また、感光体上の潜像に対するトナーの追従性が低下するために、解像性の低下、画像濃度の低下等の画質低下を招いてしまう傾向がある。
【０１５２】
本発明においては、トナー担持体上に5〜50g/m²のトナー層を形成するよう積層させることが好ましい。トナー担持体上のトナー量が5g/m²よりも小さいと、十分な画像濃度が得られにくく、トナーの帯電が過剰になることによるトナー層のムラを生じる。トナー担持体上のトナー量が50g/m²よりも多くなると、トナー飛散を生じ易くなる。
【０１５３】
また、本発明に使用されるトナー坦持体の表面粗度Ｒａ（ＪＩＳ中心線平均粗さ）は、0.2〜3.5μmの範囲にあることが好ましい。Ｒａが0.2μm未満ではトナー担持体上の帯電量が高くなり、現像性が不充分となりやすい。また、Ｒａが3.5μmを超えると、トナー担持体上のトナーの積層にむらが生じ、画像上で濃度のむらとなりやすい。表面粗度Ｒａは、0.5〜3.0μmの範囲にあることが更に好ましい。
【０１５４】
本発明において、トナー担持体の表面粗度Ｒａは、ＪＩＳ表面粗さ「JIS B 0601」に基づき、表面粗さ測定器（サーフコーダＳＥ−３０Ｈ、株式会社小坂研究所社製）を用いて測定される中心線平均粗さに相当する。具体的には、粗さ曲線からその中心線の方向に測定長さａとして2.5mmの部分を抜き取り、この抜き取り部分の中心線をＸ軸、縦倍率の方向をＹ軸、粗さ曲線をｙ＝ｆ（ｘ）で表したとき、下記式（３）によって求められる値をマイクロメートル（μm）で表したものである。
【０１５５】
【数５】

上記範囲の表面粗度（Ｒａ）を有するトナー担持体としては、アルミニウム、ステンレススチール等の金属又は合金で形成される導電性円筒が好ましく使用される。充分な機械的強度及び導電性を有する樹脂組成物で導電性円筒が形成されていても良く、導電性のゴムローラを用いても良い。また、上記のような円筒状に限らず、回転駆動する無端ベルトの形態をしても良い。また、これらに被覆層として樹脂層が用いれていても良い。
【０１５６】
本発明におけるトナー担持体の表面粗度（Ｒａ）を上記範囲にするには、例えば、トナー担持体の表層の研磨状態を変えることにより可能となる。即ち、トナー担持体表面の研磨を粗く行えば、その表面粗さを大きくすることができ、表面の研磨を細かく行えば、その表面粗さを小さくすることができる。
また、樹脂層が用いられる場合、該樹脂層に後述する導電性微粒子等を添加し、その粒径や添加量によっても表面粗さを調整できる。
【０１５７】
さらに、本発明に係わる磁性トナーは高い帯電能力を有するために、現像に際してはトナーの総帯電量をコントロールすることが好ましい。
また、本発明に係わるトナー担持体の表面は導電性微粒子及び／又は滑剤を分散した樹脂層で被覆されていることが好ましい。
【０１５８】
トナー担持体表面を被覆する樹脂層に含有される導電性微粒子としては、カーボンブラック、グラファイト、導電性酸化亜鉛等の導電性金属酸化物及び金属複酸化物を単独でもしくは２種類以上組み合わせて用いるのが好ましい。この導電性微粒子及び／又は滑剤が分散される樹脂としては、フェノール系樹脂、エポキシ系樹脂、ポリアミド系樹脂、ポリエステル系樹脂、ポリカーボネート系樹脂、ポリオレフィン系樹脂、シリコーン系樹脂、フッ素系樹脂、スチレン系樹脂、アクリル系樹脂の如き公知の樹脂が用いられる。特に熱硬化性樹脂または光硬化性の樹脂が好ましい。
【０１５９】
また、非接触の現像方法においては、現像工程でトナーを担持して現像部に搬送するトナー担持体の移動速度を、感光体の移動速度に対して速度差をもたせることが好ましい。このような速度差を設けることにより、トナー担持体側から感光体側へトナー粒子を十分に供給することができ、良好な画像を得ることができるためである。
【０１６０】
また本発明においては、トナーを担持するトナー担持体表面は、像担持体表面の移動方向と同方向に移動していてもよいし、逆方向に移動していてもよい。その移動方向が同方向である場合、像担持体の移動速度に対して、比で７０％以上であることが望ましい。７０％未満であると、画像品質が悪いことがある。移動速度比が高まれば高まるほど、現像部位に供給されるトナーの量は多く、潜像に対しトナーの脱着頻度が多くなり、不要な部分は掻き落とされ必要な部分には付与されるという繰り返しにより、潜像に忠実な画像が得られる。具体的には、トナー担持体表面の移動速度が像担持体表面の移動速度に対し、０．７〜７．０倍の速度であることが好ましい。
【０１６１】
現像部においては、該磁性トナーを静電潜像に転移させて現像するために交流電界が印加されているが、この際の交流電界は、少なくともピークトゥーピークの電界強度が3×10⁶〜1×10⁷V/mであり、周波数100〜5000Hzであることが好ましい。また、更に直流バイアスを重畳することも好ましい形態である。
【０１６２】
次に帯電工程について説明する。
本発明においては、コロナ放電を用いた帯電装置を使用する帯電工程の如き非接触の帯電工程でも構わないが、帯電部材を感光体に当接させる接触帯電法が好ましい帯電法である。この場合、接触帯電部材としては、帯電ローラを用いることが好ましい。
図１に示すような帯電ローラを用いたときの好ましいプロセス条件としては、ローラ部材の当接圧が4.9〜490N/m（5〜500g/cm）で、直流電圧または直流電圧に交流電圧を重畳したものが用いられる。直流電圧に交流電圧を重畳したものを用いる場合は、交流電圧＝0.5〜5kVpp、交流周波数＝50〜5kHz、直流電圧＝±0.2〜±5kVが好ましい。
【０１６３】
この他の帯電手段としては、帯電ブレードを用いる方法や、導電性ブラシを用いる方法がある。これらの接触帯電手段を使用する場合にも、高電圧が不要になったり、オゾンの発生が低減するといった効果がある。
【０１６４】
接触帯電部材としての帯電ローラ及び帯電ブレードの材質としては、導電性ゴムが好ましく、その表面に離型性被膜を設けてもよい。離型性被膜としては、ナイロン系樹脂、ＰＶｄＦ（ポリフッ化ビニリデン）、ＰＶｄＣ（ポリ塩化ビニリデン）、フッ素アクリル樹脂が適用可能である。
【０１６５】
接触帯電部材として用いるローラ部材の硬度は、アスカーＣ硬度が50度以下であることが好ましい。硬度が低すぎると形状が安定しないために被帯電体との接触性が悪くなり、安定した帯電性が得られない。また、硬度が高すぎると被帯電体との間に帯電当接部を確保できないだけでなく、被帯電体表面へのミクロな接触性が悪くなる。
更に、当接部を形成する帯電部材の表面の移動速度と像担持体の表面の移動速度には、相対速度差を設けることで、接触帯電部材と像担持体の当接部においてより高い接触性を得ることがでる。
【０１６６】
接触帯電部材と像担持体は、当接部において互いに逆方向に移動させることが好ましく良い。例えば、接触帯電部材を回転駆動し、さらに、その回転方向は、当接部において像担持体表面の移動方向とは逆方向に回転するように構成することが望ましい。
【０１６７】
帯電部材を像担持体表面の移動方向と同じ方向に移動させて速度差をもたせることも可能であるが、接触帯電性は像担持体の周速と帯電部材の周速の比に依存するため、逆方向と同じ周速比を得るには順方向では帯電部材の回転数が逆方向の時に比べて大きくなるので、帯電部材を逆方向に移動させる方が回転数の点で有利である。ここで記述した周速比は、下式（４）で表せる。
【０１６８】
【数６】
周速比(%)＝（帯電部材周速／像担持体周速）×100 （４）
接触帯電部材に対する印加帯電バイアスは直流電圧のみでも良好な帯電性を得ることが可能であるが、図１に示す上記装置のように直流電圧に交流電圧（交番電圧）を重畳してもよい。
【０１６９】
このときの交流電圧は、２×Ｖｔｈ（Ｖｔｈ：直流電圧印加における放電開始電圧）（Ｖ）未満のピーク電圧を有するものであるのが好ましい。
【０１７０】
直流電圧に印加される交流電圧のピーク電圧が、２×Ｖｔｈ未満でないと、 像担持体上の電位が不安定になることがあり好ましくない。直流電圧に交流電圧を重畳されたバイアスを印加する際の交流電圧として、より好ましくはＶｔｈ未満のピーク電圧を有するものである。それにより、実質的な放電現象を伴うことなく、像担持体を帯電させることができる。
次に転写工程について説明する。
【０１７１】
本発明においては、コロナ放電を用いた転写装置を使用する転写工程の如き非接触の転写工程でも構わないが、好ましくは転写部材が転写材を介して感光体に当接しており、該転写部材により転写を行う接触転写方法である。
【０１７２】
転写部材の当接圧力としては線圧2.9N/m（3g/cm）以上であることが好ましく、より好ましくは19.6N/m（20g/cm）以上である。当接圧力としての線圧が2.9N/m（3g/cm）未満であると、転写材の搬送ずれや転写不良の発生が起こりやすくなるため好ましくない。
【０１７３】
また、接触転写工程における転写部材としては、転写ローラあるいは転写ベルトを有する装置が使用される。転写ローラの一例として、少なくとも芯金と導電性弾性層からなり、導電性弾性層はカーボン等の導電材を分散させたウレタンやＥＰＤＭ等の、体積抵抗10⁶〜10¹⁰Ωcm程度の弾性体で作られており、転写バイアス電源により転写バイアスが印加されている。
【０１７４】
次に、本発明において用いられる感光体について以下に説明する。
【０１７５】
感光体としては、ａ−Ｓｅ、ＣｄＳ、ＺｎＯ₂、ＯＰＣ（有機感光体）、ａ−Ｓｉの如き光導電絶縁物質層を持つ感光ドラムもしくは感光ベルトが好適に使用される。特に、本発明においては感光体表面が高分子結着剤を主体として構成されている感光体を用いることが好ましい。例えば、セレン、アモルファスシリコンなどの無機感光体の上に樹脂を主体とした保護膜（保護層）を設ける場合、または機能分離型の有機感光体の電荷輸送層として電荷輸送材と樹脂からなる表面層を設ける場合、またその表面層の上に樹脂を主体とした保護層を設ける場合等がある。これらの表面層（または保護層）は離型性を有していることが好ましく、実際に離型性を付与する手段としては、
▲１▼膜を構成する樹脂自体に表面エネルギーの低いものを用いる、
▲２▼撥水、親油性を付与するような添加剤を加える、
▲３▼高い離型性を有する材料を粉体状にして分散させる、等の手段などが挙げられる。▲１▼の例としては、樹脂の構成単位の構造中にフッ素含有基、シリコーン含有基等の官能基を導入することが挙げられる。▲２▼の撥水、親油性を付与するような添加剤としては、例えば、界面活性剤が挙げられる。▲３▼の高い離型性を有する材料としては、フッ素原子を含む化合物、すなわちポリ４フッ化エチレン、ポリフッ化ビニリデン、フッ化カーボンが挙げられる。
【０１７６】
これらの手段によって、感光体表面の水に対する接触角を85度以上とすることができ、トナーの転写性及び感光体の耐久性を一層向上させることができる。感光体表面の水に対する接触角は、90度以上であることが好ましい。本発明においては、上記▲１▼〜▲３▼の手段の中では、▲３▼のように含フッ素樹脂等の離型性粉体の最表面層へ分散させることが好適であり、離型性粉体としてはポリ４フッ化エチレンを使用するのが特に好ましい。
【０１７７】
これらの離型性粉体を表面に含有させるためには、バインダー樹脂中に離型性粉体を分散させた層を感光体最表面に設けるか、または、感光体自体が樹脂を主体として構成されている有機感光体であれば、新たに表面層を設けなくても、最上層に離型性粉体を分散させればよい。離型性粉体の添加量は、表面層総量に対して、1〜60質量％が好ましく、2〜50質量％が更に好ましい。離型性粉体の添加量が1質量％より少ないとトナーの転写性及び感光体の耐久性改善の効果が不十分であり、60質量％を越えると保護膜の強度が低下したり、感光体への入射光量が著しく低下したりするため好ましくない。
【０１７８】
接触角の測定は、滴下式の接触角計（例えば、協和界面科学（株）の接触角計ＣＡ−Ｘ型）を用いて水の自由表面が感光体に接する場所で、液面と感光体表面のなす角（液の内部にある角）で定義する。
【０１７９】
なお、上記測定は室温（約21〜25℃）で行われるものとする。
本発明においては、帯電手段が帯電部材を感光体に当接させる接触帯電法が好ましい帯電方法であり、帯電手段が感光体に接することのないコロナ放電等による方法にくらべて感光体表面に対する負荷が大きいので、感光体の表面に保護層（保護膜）を設けることが耐久性に関する改善効果が顕著であり、好ましい適用形態の一つである。
【０１８０】
また、本発明においては、接触帯電方法、接触転写方法を適用することが好ましいため、直径が50mm以下の径が小さい感光体が特に有効に用いられる。即ち、画像形成において使用する感光体の径が小さい場合には、同一の線圧に対する曲率が大きく、当接部における圧力の集中が起こりやすいためである。ベルト感光体でも同一の現象があると考えられるが、本発明は転写部での曲率半径が25mm以下の画像形成装置に対しても有効である。
【０１８１】
本発明に用いられる感光体の好ましい様態の一つを以下に説明する。具体的には、導電性基体上に電荷発生層、次いで電荷輸送層の順で積層されている構造の積層型感光層は好ましい例の一つである。
【０１８２】
導電性基体としては、アルミニウム、ステンレスの如き金属、アルミニウム合金、酸化インジウム−酸化錫合金による被膜層を有するプラスチック、導電性粒子を含侵させた紙、プラスチック、導電性ポリマーを有するプラスチックの円筒状シリンダー及びフィルムが用いられる。
これら導電性基体上には、感光層の接着性の向上、塗工性の改良、基体の保護、基体上の欠陥の被覆、基体からの電荷注入性の改良、感光層の電気的破壊に対する保護等を目的として下引き層を設けても良い。
【０１８３】
下引き層は、ポリビニルアルコール、ポリ−Ｎ−ビニルイミダゾール、ポリエチレンオキシド、エチルセルロース、メチルセルロース、ニトロセルロース、エチレン−アクリル酸コポリマー、ポリビニルブチラール、フェノール樹脂、カゼイン、ポリアミド、共重合ナイロン、ニカワ、ゼラチン、ポリウレタン、酸化アルミニウム等の材料によって形成される。下引き層の膜厚は通常、0.1〜10μmであり、好ましくは0.1〜3μm程度である。
【０１８４】
電荷発生層は、アゾ系顔料、フタロシアニン系顔料、インジゴ系顔料、ペリレン系顔料、多環キノン系顔料、スクワリリウム色素、ピリリウム塩類、チオピリリウム塩類、トリフェニルメタン系色素、セレン、非晶質シリコン等の無機物質の様な電荷発生物質を適当な結着樹脂に分散し塗工するか、または蒸着により形成される。結着樹脂としては、例えば、ポリカーボネート樹脂、ポリエステル樹脂、ポリビニルブチラール樹脂、ポリスチレン樹脂、アクリル樹脂、メタクリル樹脂、フェノール樹脂、シリコン樹脂、エポキシ樹脂、酢酸ビニル樹脂が挙げられ、このような広範囲な樹脂から任意に結着樹脂を選択できる。電荷発生層中に含有される結着樹脂の量は、電荷発生層全体に対して80質量％以下が好ましく、0〜60質量％が更に好ましい。また、電荷発生層の膜厚は5μm以下が好ましく、特には0.05〜2μmが好ましい。
【０１８５】
電荷輸送層は、電界の存在下で電荷発生層から電荷キャリアを受け取り、これを輸送する機能を有している。電荷輸送層は電荷輸送物質を必要に応じて結着樹脂と共に溶剤中に溶解させ、塗工することによって形成される。電荷発生層の膜厚は一般的には5〜40μmである。電荷輸送物質としては、主鎖または側鎖にビフェニレン、アントラセン、ピレン、フェナントレン等の構造を有する多環芳香族化合物、インドール、カルバゾール、オキサジアゾール、ピラゾリン等の含窒素環式化合物、ヒドラゾン化合物、スチリル化合物、セレン、セレン−テルル、非晶質シリコン、硫化カドニウムが挙げられる。
【０１８６】
また、これら電荷輸送物質を分散させる結着樹脂としては、ポリカーボネート樹脂、ポリエステル樹脂、ポリメタクリル酸エステル、ポリスチレン樹脂、アクリル樹脂、ポリアミド樹脂等の樹脂、ポリ−Ｎ−ビニルカルバゾール、ポリビニルアントラセン等の有機光導電性ポリマーが挙げられる。
【０１８７】
更に、表面層として、更に別途保護層を設けてもよい。保護層の樹脂としては、ポリエステル、ポリカーボネート、アクリル樹脂、エポキシ樹脂、フェノール樹脂、またはこれらの樹脂の硬化剤を単独または２種以上組み合わせて用いることができる。
【０１８８】
また、保護層の樹脂中に導電性微粒子を分散してもよい。導電性微粒子の例としては、金属、金属酸化物が挙げられ、好ましくは、酸化亜鉛、酸化チタン、酸化スズ、酸化アンチモン、酸化インジウム、酸化ビスマス、酸化スズ被膜酸化チタン、スズ被膜酸化インジウム、アンチモン被膜酸化スズ、酸化ジルコニウムの超微粒子が挙げられる。これらの導電性微粒子は単独で用いてもよいし、２種以上を混合して用いてもよい。一般的に保護層に粒子を分散させる場合、分散微粒子による入射光の散乱を防ぐために入射光の波長よりも微粒子の粒径の方が小さいことが必要であり、本発明における保護層に分散される導電性微粒子の粒径は0.3μm以下であることが好ましい。また、保護層中での導電性微粒子の含有量は、保護層総重量に対して2〜90質量％が好ましく、5〜80質量％がより好ましい。保護層の膜厚は、0.1〜10μｍが好ましく、1〜7μmがより好ましい。
表面層の塗工は、樹脂分散液をスプレーコーティング、ビームコーティングまたは浸透（ディッピング）コーティングすることによって行うことができる。
【０１８９】
本発明においては、像担持体の帯電面に静電潜像を形成する静電潜像形成工程が、像露光手段により行われることが好ましい。静電潜像形成のための像露光手段としては、デジタル的な潜像を形成するレーザ走査露光手段に限定されるものではなく、通常のアナログ的な画像露光やＬＥＤなどの他の発光素子でも構わないし、蛍光燈等の発光素子と液晶シャッター等の組み合わせによるものなど、画像情報に対応した静電潜像を形成できるものであるなら構わない。
＜３＞本発明のプロセスカートリッジ
また、本発明は、像担持体上に形成された静電潜像をトナーを転移させて可視化してトナー像を形成し、該トナー像を転写材に転写することにより画像を形成する、本発明の画像形成方法が用いられる画像形成装置から着脱可能に構成されているプロセスカートリッジであり、感光体と、帯電手段と、現像手段とから選ばれる少なくとも２つ以上は一体に支持され、トナーは、本発明の磁性トナーであることを特徴とするプロセスカートリッジである。
＜４＞本発明に用いる物性の測定方法
本発明における各種物性データの測定法を以下に詳述する。
（１）トナー表面に存在する炭素元素の含有量（Ａ）に対する鉄元素の含有量（Ｂ）の比（Ｂ／Ａ）
本発明におけるトナー表面に存在する炭素元素の含有量（Ａ）に対する鉄元素の含有量（Ｂ）の比（Ｂ／Ａ）は、ＥＳＣＡ（Ｘ線光電子分光分析）により表面組成分析を行い算出する。
【０１９０】
本発明では、ＥＳＣＡの装置および測定条件は、下記の通りである。
使用装置：ＰＨＩ社（Physical Electronics Industries,Inc.）製
１６００Ｓ型 Ｘ線光電子分光装置
測定条件：Ｘ線源 ＭｇＫα（４００Ｗ）
分光領域800μmφ
本発明では、測定された各元素のピーク強度から、ＰＨＩ社提供の相対感度因子を用いて表面原子濃度（原子％）を算出する。
【０１９１】
測定試料としては、トナーを用いるが、トナーに外添剤が添加されている場合には、イソプロパノール等のトナーを溶解しない溶媒を用いて、トナーを洗浄し、外添剤を取り除いた後に測定を行う。
（２）トナーの平均円形度
本発明における円形度は、トナー粒子の形状を定量的に表現する簡便な方法として用いたものであり、本発明では東亜医用電子社製フロー式粒子像分析装置ＦＰＩＡ−１０００を用いてトナー粒子形状の測定を行い、円形度を下記式（２）により求める。更に下式（５）で示すように、測定された全粒子の円形度の総和を全粒子数で除した値を平均円形度と定義する。
【０１９２】
【数７】

【０１９３】
【数８】

なお、本発明で用いている測定装置である「ＦＰＩＡ−１０００」は、各トナー粒子の円形度を算出後、平均円形度の算出に当たって、トナー粒子を得られた円形度によって、円形度0.400〜1.000を0.010間隔で、0.400以上0.410未満、0.410以上0.420未満・・・0.990以上1.000未満及び1.000の様に６１分割した分割範囲に分け、分割点の中心値と頻度を用いて平均円形度の算出を行う算出法を用いている。
【０１９４】
この算出法で算出される平均円形度の各値と、上述した各粒子の円形度を直接用いる算出式によって算出される平均円形度の各値との誤差は、非常に少なく、実質的には無視できる程度であるため、本発明においては、算出時間の短縮化や算出演算式の簡略化の如きデータの取り扱い上の理由で、上述した各粒子の円形度を直接用いる算出式の概念を利用し、一部変更したこの様な算出法を用いている。
【０１９５】
本発明における円形度は、トナー粒子の凹凸の度合いを示す指標であり、トナー粒子が完全な球形の場合に1.000を示し、表面形状が複雑になる程、円形度は小さな値となる。
【０１９６】
円形度の具体的な測定方法としては、ノニオン型界面活性剤約0.1mgを溶解している水10mlにトナー約5mgを分散させ分散液を調整し、超音波（20kHz、50W）を分散液に５分間照射し、分散液濃度を5000〜20000個／μlとして、上記フロー式粒子像測定装置を用い、3μm以上の円相当径を有する粒子の円形度分布を測定する。
【０１９７】
測定の概略は、東亜医用電子社（株）発行のＦＰＩＡ−１０００のカタログ（1995年6月版）、測定装置の操作マニュアル及び特開平8-136439号公報に記載されているが、以下の通りである。
【０１９８】
試料分散液は、フラットで扁平な透明フローセル（厚み約200μm）の流路（流れ方向に沿って広がっている）を通過させる。フローセルの厚みに対して交差して通過する光路を形成するように、ストロボとＣＣＤカメラが、フローセルに対して、相互に反対側に位置するように装着される。試料分散液が流れている間に、ストロボ光がフローセルを流れているトナー粒子の画像を得るために1/30秒間隔で照射され、その結果、それぞれのトナー粒子はフローセルに平行な一定範囲を有する２次元画像として撮影される。それぞれの粒子の２次元画像の面積から、同一の面積を有する円の直径を円相当径として算出する。それぞれのトナー粒子の２次元画像の投影面積及び投影像の周囲長から上記の円形度算出式を用いて各粒子の円形度を算出する。
（３）トナーの粒度分布
測定装置としてはコールターカウンターＴＡ−ＩＩ型（コールター社製）を用い、個数分布、体積分布を出力するインターフェイス（日科機製）及びＣＸ−１パーソナルコンピュータ（キヤノン製）を接続し、電解液は１級塩化ナトリウムを用いて１％ＮａＣｌ水溶液を調製する。例えば、ＩＳＯＴＯＮ Ｒ−ＩＩ（コールターサイエンティフィックジャパン社製）を使用できる。測定法としては前記電解水溶液100〜150ml中に分散剤として界面活性剤（好ましくはアルキルベンゼンスルホン酸塩）を0.1〜5ml加え、さらに測定試料を2〜20mg加える。試料を懸濁した電解液は超音波分散器で約１〜３分間分散処理を行い、前記コールターカウンターＴＡ−ＩＩ型により、アパチャーとして100μmアパチャーを用いて、トナーの体積、個数を測定して2〜40μmの粒子の体積分布と個数分布とを算出する。それから数平均粒径（Ｄ１）体積分布から求めた重量基準の重量平均径Ｄ４（各チャンネルの中央値をチャンネルごとの代表値とする）、体積分布から求めた重量基準の12.7μm以上の重量分布を求める。
【０１９９】
【実施例】
以下、本発明を製造例および実施例により具体的に説明するが、これは本発明をなんら限定するものではない。実施例に記載されている部数または％は、質量部または質量％を示す。
＜１＞磁性体としての酸化鉄の製造
（表面処理酸化鉄１の製造）
硫酸第一鉄水溶液中に、鉄イオンに対して1.0〜1.1当量の苛性ソーダ溶液を混合し、水酸化第一鉄を含む水溶液を調製した。
【０２００】
水溶液のｐＨを９前後に維持しながら、空気を吹き込み、70℃以上で酸化反応を行い、種晶を生成させるスラリー液を調製した。次いで、このスラリー液に当初のアルカリ量（苛性ソーダのナトリウム成分）に対し0.9〜1.2当量となるよう硫酸第一鉄水溶液を加えた後、スラリー液をｐＨ８に維持して、空気を吹込みながら酸化反応をすすめ、酸化反応後に生成した磁性酸化鉄粒子を洗浄、濾過して一旦取り出した。この時、含水サンプルを少量採取し、含水量を計っておいた。
【０２０１】
次に、この含水サンプルを乾燥せずに別の水系媒体中に再分散させた後、再分散液のｐＨを約６に調製し、十分攪拌しながらシランカップリング剤（ｎ−Ｃ₁₀Ｈ₂₁Ｓｉ（ＯＣＨ₃ ）₃）を磁性酸化鉄100部に対し1.6部（磁性酸化鉄の量は含水サンプルから含水量を引いた値として計算した）添加し、カップリング処理を行った。生成した疎水性酸化鉄粒子を常法により洗浄、濾過、乾燥し、次いで若干凝集している粒子を解砕処理して、表面処理酸化鉄１を得た。尚、表面処理酸化鉄１の体積平均粒径は0.18μmであった。
（表面処理酸化鉄３の製造）
表面処理酸化鉄１の製造に於いて、シランカップリング剤の添加量を0.7部とする以外は同様にして表面処理酸化鉄３を得た。
（表面処理酸化鉄４の製造）
表面処理酸化鉄１の製造に於いて、シランカップリング剤の添加量を0.3部とする以外は同様にして表面処理酸化鉄４を得た。
（表面処理酸化鉄５の製造）
攪拌機、不活性ガス導入管、還流冷却管および温度計を備えてなるフラスコにポリビニルアルコール（ＰＶＡ−２０５、クラレ（株）製）0.1部を溶解した脱イオン水200部を仕込んだ。そこへ予め調整しておいたスチレン97.5部およびグリシジルメタクリレート2.5部からなる重合性単量体にベンゾイルパーオキサイド8部を溶解した混合物を仕込み、高速で攪拌して均一な懸濁液とした。次いで窒素ガスを吹き込みながら80℃に加熱し、この温度で５時間攪拌を続けて重合反応を行った。その後に濾過、水洗、乾燥を行って、エポキシ基を含有する樹脂を得た。
【０２０２】
一方、表面処理酸化鉄１の製造と同様に酸化反応を進め、酸化反応後に生成した磁性酸化鉄粒子を洗浄、濾過後、表面処理を行わずに、乾燥し、凝集している粒子を解砕処理し未処理酸化鉄粒子を得た。この未処理酸化鉄粒子80部と上記エポキシ基を含有する樹脂20部とをラボプラストミルを用いて180℃、100rpmの条件下に３０分間混練して、エポキシ基を含有する樹脂と未処理酸化鉄粒子とを反応させた。冷却した後、粉砕して、表面処理酸化鉄５を得た。
＜２＞磁性トナーの製造
（磁性トナーＡの製造）
イオン交換水292部に１．０Ｍ−Ｎａ₃ＰＯ₄水溶液46部を投入し70℃に加温した後、1.0M−ＣａＣｌ₂水溶液67部を徐々に添加してＣａ₃（ＰＯ₄）₂を含む水系媒体を得た。
【０２０３】
次に、スチレン83部、ｎ−ブチルアクリレート17部、ジビニルベンゼン（純度55％）0.6部、飽和ポリエステル樹脂（テレフタル酸／ビスフェノールＡ−ＥＯ、ＰＯ付加体との縮合物、Mp11000、Ｔｇ69℃、酸価12mgＫＯＨ/g）5部、負荷電性制御剤（モノアゾ染料系のＦｅ化合物）2部、α−メチルスチレンダイマー2部、表面処理酸化鉄１ 100部をアトライター（三井三池化工機（株））を用いて均一に分散混合して単量体組成物を得た。
【０２０４】
この単量体組成物を70℃に加温し、そこにＤＳＣ曲線における吸熱ピーク温度が80℃のエステルワックス12部を添加混合し、これに重合開始剤としてベンゾイルパーオキサイド5部を添加した。
【０２０５】
前記水系媒体中に上記単量体組成物を投入し、70℃、Ｎ₂雰囲気下においてＴＫ式ホモミキサー（特殊機化工業（株））にて10,000rpmで１０分間撹拌し、造粒した。その後パドル撹拌翼で撹拌しつつ、70℃で２４時間反応させた。その後懸濁液を冷却し、次いで希塩酸を添加して分散安定剤であるリン酸カルシウムを溶解し、濾過、水洗を繰り返した後、トナー粒子を得た。このトナー粒子についてＴＨＦ不溶分を測定したところ、結着樹脂成分を基準として20％であった。
【０２０６】
このトナー粒子100部と、ヘキサメチルジシラザンで表面を処理した後シリコーンオイルで処理した個数一次平均粒径10nmの疎水性シリカ微粉体1.5部とをヘンシェルミキサー（三井三池化工機（株））で混合して、磁性トナーＡを調製した。磁性トナーＡの物性を表２に示す。なお、用いた原料については表１に示す。
【０２０７】
【表１】

【０２０８】
【表２】

（磁性トナーＣの製造）
表面処理酸化鉄１の代わりに表面処理酸化鉄３を使用する以外は磁性トナーＡの製造と同様にして磁性トナーＣを調製した。磁性トナーＣの物性を表２に示す。
（磁性トナーＤの製造）
ジビニルベンゼンの代わりに不飽和ポリエステル樹脂（フマル酸／ビスフェノールＡ−ＰＯ付加体との縮合物、Mp10000、Ｔｇ65℃、酸価12mgＫＯＨ/g）2.3部を使用した以外は磁性トナーＡの製造と同様にして磁性トナーＤを調製した。磁性トナーＤの物性を表２に示す。尚、このトナー粒子についてＴＨＦ不溶分を測定したところ、結着樹脂成分を基準として35％であった。
（磁性トナーＥの製造）
α−メチルスチレンダイマーの代わりにｔ-ドデシルメルカプタンを2部添加した以外は磁性トナーＡの製造と同様にして磁性トナーＥを調製した。磁性トナーＥの物性を表２に示す。尚、このトナー粒子についてＴＨＦ不溶分を測定したところ、結着樹脂成分を基準として20％であった。
（磁性トナーＦの製造）
ベンゾイルパーオキサイドの代わりにｔ−ブチルパーオキシ−２−エチルヘキサノエートを使用した以外は磁性トナーＡの製造と同様にして磁性トナーＦを調製した。磁性トナーＦの物性を表２に示す。尚、このトナー粒子についてＴＨＦ不溶分を測定したところ、結着樹脂成分を基準として30％であった。
（磁性トナーＧの製造）
磁性トナーＡの製造で製造したトナー粒子100部と、ヘキサメチルジシラザン処理した個数一次平均粒径10nmの疎水性シリカ微粉体1.5部とをヘンシェルミキサーで混合して、磁性トナーＧを調製した。磁性トナーＧの物性を表２に示す。
（磁性トナーＨの製造）
エステルワックスの使用量を51部とする以外は磁性トナーＡの製造と同様にして、磁性トナーＨを得た。磁性トナーＨの物性を表２に示す。
（磁性トナーＩの製造）
エステルワックスの使用量を0.4部とする以外は磁性トナーＡの製造と同様にして、磁性トナーＩを得た。磁性トナーＩの物性を表２に示す。
（磁性トナーＪの製造）
エステルワックスに代えてＤＳＣにおける吸熱ピーク温度が112℃の低分子量ポリエチレンワックスを12部用いる以外は磁性トナーＡの製造と同様にして、磁性トナーＪを得た。磁性トナーＪの物性を表２に示す。
（磁性トナーＫの製造）
表面処理酸化鉄１の代わりに表面処理酸化鉄４を使用する以外は磁性トナーＡの製造と同様にして、比較用磁性トナーＫを得た。比較用磁性トナーＫの物性を表２に示す。
（磁性トナーＬの製造）
表面処理酸化鉄１の代わりに表面処理酸化鉄５を120部使用する以外は磁性トナーＡの製造と同様にして、比較用磁性トナーＬを得た。比較用磁性トナーＬの物性を表２に示す。
【０２０９】
（磁性トナーＭの製造）
イオン交換水730部に1.0M−Ｎａ₃ＰＯ₄水溶液46部を投入し６０℃に加温した後、1.0M−ＣａＣｌ₂水溶液67部を徐々に添加してＣａ₃（ＰＯ₄）₂を含む水系媒体を得た。
【０２１０】
次に、スチレン80部、ｎ−ブチルアクリレート20部、ジビニルベンゼン0.6部、負荷電性制御剤（モノアゾ染料系のＦｅ化合物）1部、表面処理酸化鉄５ 120部をアトライターを用いて均一に混合、分散した。
【０２１１】
次いで、この分散物を60℃に加温し、そこにＤＳＣにおける吸熱ピーク温度が80℃のエステルワックス12部を添加混合し、これに重合開始剤として２，２'−アゾビス（２，４−ジメチルバレロニトリル）（Ｖ６５）３部と２，２'−アゾビスイソブチロニトリル（ＡＩＢＮ）４部を添加して単量体組成物を得た。
【０２１２】
前記水系媒体中に上記単量体組成物を投入し、60℃、Ｎ₂雰囲気下においてＴＫ式ホモミキサーにて10,000rpmで１０分間撹拌し、造粒した。その後パドル撹拌翼で撹拌しつつ、60℃で１０時間反応させた。
【０２１３】
反応終了後、懸濁液を冷却し、希塩酸を加えてｐＨ１．０として１時間撹拌した。その後、濾過、乾燥して重量平均粒径7.0μmのトナーを得た。
【０２１４】
このトナー粒子100部と、磁性トナーＡの製造で使用した疎水性シリカ微粉体1.5部とをヘンシェルミキサーで混合して、比較用磁性トナーＭを調製した。比較用磁性トナーＭの物性を表２に示す。尚、このトナー粒子についてＴＨＦ不溶分を測定したところ、結着樹脂成分を基準として65％であった。
（磁性トナーＮの製造）
ビスフェノールＡのＰＯ付加物369.5 g、ビスフェノールＡのＥＯ付加物146.4 g、テレフタル酸126.0 g、ドデセニルコハク酸40.2 g、無水トリメリット酸77.7 gをガラス製の４つ口フラスコに入れ、温度計、ステンレス製攪拌棒、コンデンサー、及び窒素導入管を取り付け、マントルヒータ中で、窒素気流下にて220℃にて反応させた。重合度は、ASTM E28-67に準拠した軟化点より追跡を行い、軟化点が110℃に達したとき、反応を終了した。
次に、スチレン65部、２−エチルヘキシルアクリレート35部、ジビニルベンゼン0.8部、表面処理酸化鉄５ 120部に、上記にて合成したポリエステル樹脂を10部、２，２'−アゾビスイソブチロニトリル3.5部を添加し、アトライターに投入し、10℃にて５時間分散し、重合性単量体組成物を得た。
次いで、２リットルのガラス製セパラブルフラスコに予め調製したリン酸三カルシウム4％の水性コロイド溶液650部に対して前記の重合性単量体組成物212.3部を添加し、ＴＫホモミキサーを用いて室温にて、回転数10000rpmで２分間造粒した。
【０２１５】
次に、４つ口ガラス製の蓋をし、還流冷却管、温度計、窒素導入管、ステンレス製攪拌棒を取り付け、電熱マントルヒータ中に設置した。窒素下にて攪拌を続けながら、１段目の重合として85℃まで昇温し、１０時間反応を行い種粒子とした。これを室温まで冷却して前駆体粒子を得た。次に、該前駆体粒子の水系懸濁液中に超音波発振機にて調製したスチレン13部、２−エチルヘキシルアクリレート7部、２，２'−アゾビスイソブチロニトリル（ＡＩＢＮ）0.4部、ジビニルベンゼン0.22部、ラウリル硫酸ナトリウム0.1部、水20部からなる水乳濁液40.7部を滴下し、該前駆体粒子を膨潤させた。
【０２１６】
その後、窒素下にて攪拌を続けながら２段目の重合として85℃まで昇温し、１０時間反応させた。冷却後、10％塩酸水溶液にて分散媒を溶かし、濾過、水洗を経て風乾後45℃にて１２時間、20mmHgで減圧乾燥し、風力分級機にて分級し、重量平均粒径7.8μmのトナー粒子を得た。このトナー粒子についてＴＨＦ不溶分を測定したところ、結着樹脂成分を基準として35％であった。
【０２１７】
このトナー粒子100部と、磁性トナーＡの製造で使用した疎水性シリカ微粉体1.5部とをヘンシェルミキサーで混合して、磁性トナーＮを調製した。磁性トナーＮの物性を表２に示す。
（磁性トナーＯの製造）
磁性トナーＬの製造で得られたトナー粒子Ｌを160℃に加熱した二軸エクストルーダーで溶融混練した。その後、冷却した混練物をハンマーミルで粗粉砕し、粗粉砕物をジェットミルで微粉砕した。さらに得られた粉砕物の分級を行なった。この分級粉についてＴＨＦ不溶分を測定したところ、結着樹脂成分を基準として0％であった。
【０２１８】
この分級粉100部と、磁性トナーＡの製造で使用した疎水性シリカ微粉体1.5部とをヘンシェルミキサーで混合して、磁性トナーＯを調製した。磁性トナーＯの物性を表２に示す。
（磁性トナーＰの製造）
磁性トナーＯの製造で得られた分級粉を機械的衝撃力により表面改質（球形化）処理しトナー粒子を得た。このトナー粒子100部と、磁性トナーＡの製造で使用した疎水性シリカ微粉体1.5部とをヘンシェルミキサーで混合して、磁性トナーＰを調製した。磁性トナーＰの物性を表２に示す。
（磁性トナーＱの製造）
反応容器にキシレン200部を入れ還流温度まで昇温した。これにスチレン83部、ｎ-ブチルアクリレート17部、及び、ジ−ｔｅｒｔ―ブチルパーオキサイド2.0部の混合液を滴下後、キシレン還流下、７時間で溶液重合を完了し、キシレンを留去して低分子量樹脂を得た。
【０２１９】
一方、別の反応容器にスチレン83部、ｎ-ブチルアクリレート17部、ジビニルベンゼン0.5部、ポリビニルアルコール0.2部、水200部、ベンゾイルパーオキサイド0.3部を混合し、懸濁分散させた。上記懸濁分散溶液を加熱し、窒素雰囲気下において80℃に２４時間保持し、冷却の後にろ過を行い水洗、乾燥し、高分子量樹脂の粒子を得た。尚、この樹脂粒子のＴＨＦ不溶分を測定したところ、73％であった。
【０２２０】
次に、高分子量樹脂粒子40部、低分子量樹脂60部、負荷電性制御剤（モノアゾ染料系のＦｅ化合物）2部、表面処理酸化鉄５ 120部、最大吸熱ピーク80℃のエステルワックス12部をブレンダーにて混合し、これを160℃に加熱した二軸エクストルーダーで溶融混練し、冷却した混練物をハンマーミルで粗粉砕した後、粗粉砕物をジェットミルで微粉砕した。
次いで、得られた粒子の表面改質（球形化）処理を行い、その後分級した。この分級粉についてＴＨＦ不溶分を測定したところ、結着樹脂成分を基準として2％であった。
【０２２１】
さらに、分級粉100部と磁性トナーＡの製造で使用した疎水性シリカ微粉体1.5部とをヘンシェルミキサーで混合して、磁性トナーＱを調製した。磁性トナーＱの物性を表２に示す。
（磁性トナーＲの製造）
反応容器にエチレングリコールジメタクリレート1.2部、ｎ-ドデシルメルカプタン1.1部、スチレン83部、ｎ-ブチルアクリレート17部、アゾビスイソブチロニトリル2.4部、ポリビニルアルコール０．２部、水200部を混合し、懸濁分散させた。上記懸濁分散溶液を加熱し、窒素雰囲気下において90℃に10時間保持し、冷却の後にろ過を行い水洗、乾燥し、高分子量樹脂の粒子を得た。尚、この樹脂粒子のＴＨＦ不溶分を測定したところ、25％であった。
【０２２２】
次に、高分子量樹脂粒子100部、負荷電性制御剤（モノアゾ染料系のＦｅ化合物）2部、表面処理酸化鉄５ 120部、最大吸熱ピーク80℃のエステルワックス12部をブレンダーにて混合し、これを160℃に加熱した二軸エクストルーダーで溶融混練し、冷却した混練物をハンマーミルで粗粉砕した後、粗粉砕物をジェットミルで微粉砕した。
次いで、得られた粒子の表面改質（球形化）処理を行い、その後分級した。この分級粉についてＴＨＦ不溶分を測定したところ、結着樹脂成分を基準として1％であった。
さらに、分級粉100重量部と磁性トナーＡの製造で使用した疎水性シリカ微粉体1.5部をヘンシェルミキサーで乾式混合して、磁性トナーＲを調製した。磁性トナーＲの物性を表２に示す。
＜３＞感光体の製造
（感光体１の製造）
感光体としては直径30mmのAlシリンダを導電性基体とした。これに、下記に示すような構成の層を順次浸漬塗布により積層して、感光体を作成した。
（1）導電性被覆層：酸化錫及び酸化チタンの粉末をフェノール樹脂に分散したものを主体とする。膜厚15μm。
（2）下引き層：変性ナイロン、及び共重合ナイロンを主体とする。膜厚0.6μm。
（3）電荷発生層：長波長域に吸収を持つアゾ系顔料をポリビニルブチラール樹脂に分散したものを主体とする。膜厚0.6μm。
（4）電荷輸送層：ホール搬送性トリフェニルアミン化合物をポリカーボネート樹脂（オストワルド粘度法による分子量2万）に8：10の質量比で溶解したものを主体とし、さらにポリ4フッ化エチレン粉体（粒径0.2μm）を総固形分に対して10質量%添加し、均一に分散した。膜厚25μm。水に対する接触角は95度であった。
なお、接触角の測定は、純水を用い、装置は、協和界面科学（株）、接触角計ＣＡ−Ｘ型を用いた。
【０２２３】
【実施例１〜１０および比較例１〜８】
画像形成装置として、ＬＢＰ−１７６０を改造し、上述の実施の形態と同様の図1に示されるものを用いた。
静電荷像坦持体としては有機感光体（ＯＰＣ）ドラムを用いた。この感光体に、一次帯電部材として導電性カーボンを分散しナイロン樹脂で被覆されたゴムローラ帯電器を当接させ（当接圧60g/cm）、直流電圧−700Vdcに交流電圧2.0 kVppを重畳した電圧を印加して感光体上を一様に帯電する。一次帯電に次いで、レーザー光で画像部分を露光することにより静電潜像を形成する。この時、暗部電位Vd＝−700V、明部電位VL＝-150Vとした。
【０２２４】
感光ドラムと現像スリーブとの間隙は290μmとし、トナー担持体として下記の構成の層厚約7μm、ＪＩＳ中心線平均粗さ（Ra）1.0μmの樹脂層を、表面をブラストした直径16mmのアルミニウム円筒上に形成した現像スリーブを使用し、現像磁極90mT（900ガウス）、トナー層厚規制部材として厚み1.0mm、自由長1.0mmのシリコーンゴム製ブレードを29.4N/m（30g/cm）の線圧で当接させた。
・フェノール樹脂 100部
・グラファイト（粒径約7μm） 90部
・カーボンブラック 10部
次いで、現像バイアスとして直流バイアス成分Ｖｄｃ＝-500V、重畳する交流バイアス成分Ｖp-p＝1600V、f＝2000Hzを用いた。また、現像スリーブの周速は感光体周速（90mm/sec）に対して順方向に110％の周速比（99mm/sec）とした。
また、転写部材として、転写ローラ（導電性カーボンを分散したエチレン-プロピレンゴム製、導電性弾性層の体積抵抗値10⁸Ωcm、表面ゴム硬度24゜、直径20mm、当接圧59 N/m(60g/cm)）を感光体周速（90mm/sec）に対して等速とし、転写バイアスは直流1．5kVとした。
定着方法としてはＬＢＰ−１７６０のオイル塗布機能のない、フィルムを介してヒータにより加熱加圧定着する方式の定着装置を用いた。この時加圧ローラはフッ素系樹脂の表面層を有するものを使用し、ローラの直径は30mmであった。また、定着温度は180℃、ニップ幅を6mmに設定した。
トナーとして磁性トナーＡ〜Ｒを使用し、常温、常湿（25℃、60％ＲＨ）および低温、低湿（10℃、15％ＲＨ）環境下において、それぞれ100枚の画出し試験を行った。尚、転写材としては75g/m²の紙を使用した。
磁性トナーＡ〜Ｒの評価は以下のようにして行った。
[プリントアウト画像の評価]
１）画像濃度
常温常湿下における50枚目のプリントアウト画像について、マクベス反射濃度計RD918（マクベス社製）により、原稿濃度が0.00の白地部分のプリントアウト画像に対する相対濃度を測定した。
Ａ：非常に良好（1.40以上）
Ｂ：良好（1.35以上、1.40未満）
Ｃ：普通（1.00以上、1.35未満）
Ｄ：悪い（1.00未満）
２）カブリ
低温低湿下での100枚目のプリントアウト画像について、白地部分の白色度と転写紙の白色度の差から、カブリ濃度（％）をそれぞれ算出し、画像カブリを評価した。尚、カブリ濃度は「リフレクトメーター」（東京電色社製）により測定した。
Ａ：非常に良好（1.5％未満）
Ｂ：良好（1.5％以上、2.5％未満）
Ｃ：普通（2.5％以上、4.0％未満）
Ｄ：悪い（4.0％以上）
３）転写性
ベタ黒画像形成時の感光体上の転写残トナーを、マイラーテープによりテーピングしてはぎ取り、はぎ取ったマイラーテープを紙上に貼ったもののマクベス濃度から、マイラーテープのみを紙上に貼ったもののマクベス濃度を差し引いた数値で評価した。
Ａ：非常に良好（0.05未満）
Ｂ：良好（0.05以上乃至0.1未満）
Ｃ：普通（0.1以上乃至0.2未満）
Ｄ：悪い（0.2以上）
４）定着性
低温低湿下での２枚目のプリントアウト画像について、50g/cm²の荷重をかけ、柔和な薄紙により定着画像を摺擦し、摺擦前後での画像濃度の低下率（％）で評価した。
Ａ：5％未満
Ｂ：5％以上、10％未満
Ｃ：10％以上、20％未満
Ｄ：20％以上
［画像形成装置とのマッチング評価］
１）感光体とのマッチング
プリントアウト試験終了後、感光体ドラム表面の傷や残留トナーの固着の発生状況とプリントアウト画像への影響を目視で評価した。
Ａ：未発生
Ｂ：わずかに傷の発生が見られる
Ｃ：固着や傷がある
Ｄ：固着が多い
２）定着器とのマッチング
プリントアウト試験終了後、定着フィルム表面の傷や残留トナーの固着状況を目視で評価した。
Ａ：未発生
Ｂ：わずかに固着が見られる
Ｃ：固着や傷がある
Ｄ：固着が多い
得られた結果を表３に示す。
【０２２５】
【表３】

【０２２６】
本発明により、帯電均一性と定着性に優れ、高精細な画像を得ることができる磁性トナーを提供できる。
【図面の簡単な説明】
【図１】 本発明の画像形成方法を実施するための画像形成装置の概略構成図を示す。
【図２】 本発明の画像形成方法を実施するための画像形成装置の概略構成図を示す。
【符号の説明】
１００ 感光ドラム
１０２ 現像スリーブ（トナー担持体）
１０４ マグネットローラ
１１４ 転写ローラ
１１６ クリーナ
１１７ 帯電ローラ（接触帯電部材）
１２１ レーザー発生装置
１２４ レジスタローラ
１２５ 搬送ベルト
１２６ 定着器
１４０ 現像器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic toner and an image forming method used in a recording method using an electrophotographic method, an electrostatic recording method, a magnetic recording method, a toner jet recording method, or the like. More specifically, the present invention relates to a magnetic toner for use in a copying machine, a printer, a fax machine, an image forming method, and a process in which a toner image is previously formed on an electrostatic latent image carrier and then transferred onto a transfer material to form an image. It relates to the cartridge.
[0002]
[Prior art]
Conventionally, a number of methods are known as electrophotographic methods. In general, an electric latent image is formed on an electrostatic image bearing member (hereinafter referred to as a “photosensitive member”) using a photoconductive substance by various means. Then, the latent image is developed with toner to form a visible image. If necessary, the toner image is transferred to a transfer material such as paper, and then the toner image is fixed on the transfer material by heat and pressure. To obtain a copy.
[0003]
As a method for visualizing an electric latent image, a cascade development method, a magnetic brush development method, a pressure development method, and the like are known.
[0004]
U.S. Pat. No. 3,909,258 proposes a developing method using an electrically conductive magnetic toner. In this method, a conductive magnetic toner is supported on a cylindrical conductive sleeve having magnetism inside, and is developed by bringing it into contact with an electrostatic image. At this time, a conductive path is formed by toner particles between the surface of the recording member and the sleeve surface in the developing unit, and electric charges are guided from the sleeve to the toner particles through this conductive path, and between the image part of the electrostatic image. The toner particles adhere to the image area and are developed by the Coulomb force. The developing method using the conductive magnetic toner is an excellent method that avoids the problems associated with the conventional two-component developing method. However, since the toner is conductive, the developed image is transferred from the recording medium to plain paper or the like. There is a problem that it is difficult to electrostatically transfer to the final support member.
[0005]
As a developing method using a high-resistance magnetic toner that can be electrostatically transferred, there is a developing method using dielectric polarization of toner particles. However, this method has problems such as a slow development speed and insufficient density of the developed image, and is difficult in practical use.
[0006]
As another developing method using a high-resistance insulating magnetic toner, the toner particles are frictionally charged by friction between the toner particles, friction between the toner particles and the sleeve, and the like, and then contact the electrostatic image holding member. A developing method is known. However, this method requires less contact between the toner particles and the friction member, and the magnetic toner used has a large amount of magnetic material exposed on the surface of the toner particles. There are problems such as.
[0007]
For example, in JP-A-54-43027 and JP-A-55-18656, a magnetic developer is thinly applied on a developer carrier, and this is triboelectrically charged. And a so-called jumping development method is disclosed in which the electrostatic latent image is brought very close to each other and opposed to each other without contact. According to this method, the magnetic developer is thinly coated on the developer carrying member to enable sufficient frictional charging of the developer, and the developer is supported without being in contact with the electrostatic latent image while being magnetically supported. Therefore, the transfer of the developer to the non-image area, so-called fogging, is suppressed, and a high-definition image can be obtained.
[0008]
Such a one-component development method does not require carrier particles such as glass beads or iron powder as in the two-component method, and therefore the development device itself can be reduced in size and weight. Furthermore, since the two-component development method needs to keep the toner concentration in the developer constant, a device for detecting the toner concentration and supplying a necessary amount of toner is necessary. Therefore, the developing device is also large and heavy here. The one-component development method is preferable because such an apparatus is not necessary, and can be made small and light.
[0009]
However, the developing method using the insulating magnetic toner has unstable elements related to the insulating magnetic toner to be used. This is because a considerable amount of fine powdery magnetic material is mixed and dispersed in the insulating magnetic toner, and a part of the magnetic material is exposed on the surface of the toner particles. As a result, various characteristics required for the magnetic toner, such as development characteristics and durability of the magnetic toner, are changed or deteriorated.
[0010]
When the magnetic toner containing the conventional magnetic body is used, the above-mentioned problem occurs because the magnetic body is exposed on the surface of the magnetic toner. That is, by exposing magnetic fine particles having a relatively low resistance compared to the resin constituting the toner to the surface of the magnetic toner, the toner charging performance is lowered, the toner fluidity is lowered, and a long-term In use, the deterioration of the developer, such as a decrease in image density due to the separation of the magnetic material due to the rubbing between the toners or the regulating member, and the occurrence of shading unevenness called sleeve ghost, is caused.
[0011]
Conventionally, proposals regarding magnetic iron oxide contained in a magnetic toner have been made, but there are still points to be improved.
[0012]
For example, Japanese Patent Application Laid-Open No. 62-279352 proposes a magnetic toner containing magnetic iron oxide containing silicon element. Such magnetic iron oxide intentionally has silicon element present inside the magnetic iron oxide, but still has a point to be improved in the fluidity of the magnetic toner containing the magnetic iron oxide.
[0013]
In Japanese Patent Publication No. 3-9045, a proposal is made to control the shape of magnetic iron oxide to be spherical by adding silicate. The magnetic iron oxide obtained by this method uses silicate to control the particle shape, so that a large amount of silicon element is distributed inside the magnetic iron oxide, and the amount of silicon element present on the magnetic iron oxide surface is small. Since the smoothness of the magnetic iron oxide is high, the fluidity of the magnetic toner is improved to some extent, but the adhesion between the binder resin constituting the magnetic toner and the magnetic iron oxide is insufficient.
[0014]
Japanese Patent Application Laid-Open No. 61-34070 proposes a method for producing iron trioxide by adding a hydrosilosilicate solution during the oxidation reaction to iron trioxide. Although the iron tetroxide by this method has Si element near the surface, the Si element exists in a layer near the iron tetroxide surface, and the surface is weak against mechanical impact such as friction. Has a point.
[0015]
On the other hand, the toner is manufactured as a toner having a desired particle size by melting and mixing a binder resin, a colorant, and the like, uniformly dispersing, pulverizing with a fine pulverizer, and classifying with a classifier (pulverization method). However, there is a limit to the range of materials that can be used to reduce the toner particle size. For example, the resin colorant dispersion must be sufficiently brittle and capable of being finely pulverized by an economically usable production apparatus. From this requirement, in order to make the resin colorant dispersion brittle, when the resin colorant dispersion is actually finely pulverized at a high speed, particles having a wide particle size range are easily formed, and in particular, a relatively large proportion of fine particles ( There arises a problem that excessively pulverized particles) are included therein. Further, such highly brittle materials are often further pulverized or powdered when used as developing toners in copying machines and the like.
[0016]
Also, in the pulverization method, it is difficult to completely disperse solid fine particles such as magnetic powder or colorant into the resin, and depending on the degree of dispersion, fogging may increase and image density may decrease. . Furthermore, the pulverization method inherently exposes the magnetic iron oxide particles on the surface of the toner, so that problems still remain in the fluidity of the toner and the charging stability in a harsh environment.
[0017]
That is, in the pulverization method, there is a limit to finer toner particles required for high definition and high image quality, and accordingly, powder characteristics, particularly toner uniform chargeability and fluidity, are significantly attenuated.
[0018]
In order to overcome the problems of the toner by the pulverization method as described above, and further to satisfy the above-described requirements, a toner production method by a suspension polymerization method has been proposed.
[0019]
The toner by suspension polymerization (hereinafter referred to as polymerized toner) can be easily made into fine particles of toner, and further, since the shape of the obtained toner is spherical, it has excellent fluidity and is advantageous for high image quality. It becomes.
[0020]
However, when the polymerized toner contains a magnetic substance, its fluidity and charging characteristics are significantly lowered. This is because magnetic particles are generally hydrophilic and thus easily exist on the toner surface. In order to solve this problem, it is important to modify the surface characteristics of the magnetic material.
[0021]
Many proposals have been made regarding surface modification for improving the dispersibility of a magnetic substance in a polymerized toner. For example, various silane coupling agent treatment techniques for magnetic materials are disclosed in JP-A-59-200254, JP-A-59-200256, JP-A-59-200257, and JP-A-59-224102. Japanese Laid-Open Patent Publication No. 63-250660 discloses a technique for treating silicon element-containing magnetic particles with a silane coupling agent, and Japanese Laid-Open Patent Publication No. 7-72654 discloses magnetic iron oxide as an alkyl. Techniques for treating with trialkoxysilanes are disclosed.
[0022]
However, although the dispersibility in the toner is improved to some extent by these treatments, there is a problem that it is difficult to uniformly hydrophobize the surface of the magnetic material. The generation of non-magnetic particles cannot be avoided, and this is insufficient to improve the dispersibility in the toner to a good level.
[0023]
Also, a special toner in which magnetic particles are contained only in a specific portion inside the particles has already been disclosed in JP-A-7-209904.
[0024]
However, Japanese Patent Laid-Open No. 7-209904 does not mention the circularity of the disclosed toner.
[0025]
Further, to summarize the toner configuration disclosed in Japanese Patent Application Laid-Open No. 7-209904, it is composed of a structure in which a resin layer having no magnetic particles is formed in the vicinity of the toner particle surface with a certain thickness or more. Yes, this means that there is a considerable proportion of the toner surface layer where no magnetic particles are present. However, in other words, when the average particle size is as small as 10 μm, for example, such a developer has a small volume in which magnetic particles can exist, and therefore it is difficult to enclose a sufficient amount of magnetic particles. In addition, in such a developer, the ratio of the surface resin layer in which the magnetic particles do not exist is different between the developer particles having a large particle size and the developer particles having a small particle size in the particle size distribution of the developer. The content of the magnetic substance contained in the developer is different, and the developability and transferability are also different depending on the particle size of the developer, that is, selective developability depending on the particle size is easily observed. Therefore, if printing is performed for a long time with a magnetic developer with a non-uniform particle size, particles that contain a large amount of magnetic material and are difficult to develop, that is, developer particles with a large particle size are likely to remain, and the image density and image quality are lowered. It also leads to deterioration.
[0026]
On the other hand, LED and laser beam printers are the mainstream in the recent market, and the direction of technology is higher resolution, that is, what was traditionally 240, 300 dpi is 400, 600, 800 dpi. . Accordingly, the development method is also required to have higher definition.
In addition, copying machines are becoming more sophisticated, and thus are moving toward digitalization. Since this method is mainly a method of forming an electrostatic charge image with a laser, it is also proceeding in the direction of high resolution. In this case, a high-resolution and high-definition developing method has been demanded as in the case of a printer. Japanese Patent Laid-Open Nos. 1-112253 and 2-284158 propose toners having a small particle size. However, the toner having a small particle diameter has a more difficult uniform dispersibility and inclusion property of the magnetic powder, and the various problems described above have not been sufficiently solved.
[0027]
Further, a method of adding inorganic fine particles as external additives to toner base particles has been proposed and widely used for the purpose of improving toner flow characteristics, charging characteristics, and the like.
For example, inorganic fine particles that have been hydrophobized in JP-A-5-66608, JP-A-4-9860, etc., or inorganic fine particles that have been hydrophobized and then treated with silicone oil or the like are added, or -249059, JP-A-4-264453, and JP-A-5-346682 disclose a method of adding hydrophobized inorganic particles and silicone oil-treated inorganic particles in combination.
However, these proposals also have room for further improvement in the above-described problems when toner particles having a smaller particle diameter are used in order to increase the resolution.
[0028]
In recent years, space saving, cost reduction, and low power consumption due to downsizing of copiers and printers have become very important issues, and fixing devices are also required to be downsized, simplified and low power consumption. It is coming. Accordingly, it is necessary to reduce the viscosity of the toner at the time of melting and increase the adhesion area with the fixing substrate so that the toner can exhibit sufficient fixability with a low heat quantity and low pressure. It is required to lower the Tg and molecular weight of the binder resin. However, toners mainly composed of soft components are difficult to achieve both high-temperature offset resistance, and further have problems such as difficulty in developing properties and storage characteristics and easy sticking to the photoreceptor.
[0029]
Various proposals have been made for the improvement of fixing ability since ancient times. For example, in Japanese Examined Patent Publication No. 51-23354, a monomer such as styrene is polymerized in the presence of a crosslinking agent and a molecular weight modifier to obtain a moderately crosslinked resin, and this is kneaded and pulverized with carbon black or the like. Thus, a pulverized toner having improved high-temperature offset resistance and low-temperature fixability has been proposed. Japanese Patent No. 2681791 discloses a pulverized toner obtained by melt-kneading and pulverizing a styrene-based binder resin containing 10 to 60% by weight of a THF-insoluble component based on a binder resin together with a magnetic substance, a charge control agent and a wax. Has been. According to these publications, a toner having improved high-temperature offset resistance and low-temperature fixability can be obtained by cutting the THF-insoluble component (crosslinking component) of the binder resin by melt-kneading to produce a high molecular weight component. . However, as long as such a method of thermally and mechanically cleaving the insoluble matter of the binder resin is taken, the soluble component generated by the cleavage of the molecular chain has a considerably wide molecular weight distribution. Therefore, there is almost no effect on the high temperature resistant offset, and many intermediate molecular weight components that inhibit the low temperature fixability are generated, and it is difficult to say that the compatibility between the low temperature fixability and the high temperature offset resistance is achieved.
[0030]
Japanese Patent Application Laid-Open No. 5-06029 discloses that the crosslinking is cut with a shearing force by heating and kneading a binder resin having two or more vinyl groups and a carboxyl group-containing binder resin and an organometallic compound. However, a method for producing a pulverized toner is disclosed in which a carboxyl group and a metal ion are subjected to metal cross-linking so that a component ratio of 5000000 or more in a molecular weight distribution of a binder resin component is 5% or more and Mw is 5000000 or more. According to this gazette, a toner having excellent high-temperature offset resistance can be obtained. However, in this case as well, an intermediate molecular weight component is always generated, so there is room for further improvement in low-temperature fixability. Furthermore, the above listed pulverized toners have the problem that their circularity is low and the transfer efficiency is low, and because many magnetic powders are exposed on the surface of the toner particles, the flowability and uniformity of the toner are reduced. There is a problem with chargeability.
[0031]
On the other hand, in the case of the polymerized toner, unlike the pulverized toner, the toner can be directly produced without going through the melt-kneading process, so that the insoluble matter (crosslinking component) generated during the polymerization is not cut and the offset toner is extremely resistant to offset. It is excellent in that a high toner can be obtained. However, on the other hand, the insoluble matter has a great effect of inhibiting the low-temperature fixability, and it is possible to balance the low-temperature fixability and the high-temperature offset resistance by minimizing the insoluble content. is required.
[0032]
Japanese Patent Application Laid-Open No. 11-38678 discloses a non-magnetic polymerized toner in which components having a molecular weight of 1000000 or more are 0 to 20%, THF insolubles are 0 to 60%, and the total of these is 1 to 60%. However, this publication discloses a technique for a non-magnetic toner, and there is room for improvement for a magnetic polymer toner containing magnetic powder.
Furthermore, Japanese Patent No. 2749234 discloses a method for producing a magnetic toner in which the wax component in the toner is fibrous, in which a polymerizable cross-linking agent is added to a monomer composition containing magnetic powder. In addition, a magnetic polymerization toner is obtained by using an azo polymerization initiator.
[0033]
Japanese Patent No. 2749122 discloses a method of surface-treating magnetic powder with a polymer having a specific reactive group, in which the polymerizable crosslinking agent is a monomer containing magnetic powder. A magnetic polymerized toner is obtained by adding to the composition and using an azo polymerization initiator. However, as estimated from the addition amount of the crosslinking agent, the type and addition amount of the polymerization initiator, and the polymerization temperature described in these publications, an intermediate amount caused by excessive generation of THF insolubles or very weak crosslinking Since the ratio of the molecular weight component is increased, there is a problem in fixability in the case of a magnetic toner containing a large amount of magnetic powder. In addition, the magnetic polymer toners obtained by these publications have insufficient hydrophobization treatment of the magnetic powder used, and have problems in fluidity and charging characteristics.
[0034]
For the purpose of improving the low-temperature fixability of the toner, it is known to polymerize a monomer in the presence of a chain transfer agent in the production of a toner resin. For example, in JP-A-58-11955, a high molecular weight resin is first produced by suspension polymerization of styrene and an acrylic monomer, and then a monomer such as styrene and an α-methylstyrene dimer which is a chain transfer agent are added. Further, a mixture of high molecular weight resin and low molecular weight resin is obtained by polymerization. However, the resin produced according to this publication has insufficient high-temperature offset resistance. Further, Japanese Patent No. 2965883 discloses a toner having a small content of fine particles obtained by polymerizing a monomer composition containing a colorant and α-methylstyrene dimer, and then agglomerating heat treatment and crushing. However, since the toner does not contain a cross-linking agent in the monomer composition, it does not contain any insoluble matter or high molecular weight component, which causes a problem in high temperature offset resistance. JP-A-9-230628 discloses a composition comprising a colorant, a wax, and a monomer in the presence of a chain transfer agent such as t-dodecyl mercaptan and α-methylstyrene dimer, and then polymerizes by emulsion polymerization. Further, a toner aggregated by heating is disclosed. However, since there is no insoluble matter, there is a problem in high temperature offset resistance.
[0035]
Conventionally, as an image forming method, many methods such as an electrostatic recording method, a magnetic recording method, and a toner jet method are known. For example, electrophotography generally forms an electrical latent image on a photoreceptor using a photoconductive substance as a latent image carrier by various means, and then develops the latent image with toner. A visible image is formed, and a toner image is transferred onto a recording medium such as paper as necessary, and then the toner image is fixed on the recording medium by heat, pressure, or the like to obtain an image.
In general, when a toner having a high and uniform charge amount distribution is used, the transfer efficiency is high. However, as described above, such a toner has not been obtained with a magnetic toner.
[0036]
Also, spherical toner is said to have high transfer efficiency due to its shape. In this regard, Japanese Patent Application Laid-Open No. 61-279864 proposes to specify the shape factors SF1 and SF2, and Japanese Patent Application Laid-Open No. 63-235953 proposes a magnetic toner that is spheroidized by a mechanical impact force. . However, the transfer efficiency of these toners is still insufficient and further improvement is required.
[0037]
On the other hand, such a spherical toner has an advantage that the transfer efficiency is higher than that of the pulverized toner, but has a property of being hard to be cleaned because of the spherical shape. Further, as described above, the toner particle diameter is directed toward the smaller particle diameter, and it is more difficult to completely clean the transfer residual toner. However, through the improvement of the cleaning device or the like, it is possible to suppress the toner slipping to a level that does not cause a big problem. In the image forming method having the conventional corona charging method, an image having no practical problem can be formed. It was possible. However, in recent years, from the viewpoint of environmental protection, primary charging using a corona discharge, which has been used in the past, and primary transfer (contact charging) using a photoreceptor contact member that has great advantages such as low ozone and low power. ) And transfer processes (contact transfer) are becoming mainstream.
[0038]
For example, Japanese Patent Laid-Open Nos. 63-149669 and 2-123385 have been proposed. These relate to a contact charging method and a contact transfer method, a conductive elastic roller is brought into contact with the photosensitive member, and the surface of the photosensitive member is uniformly charged while applying a voltage to the conductive roller. After obtaining a toner image by the development process, the transfer material is passed while pressing another conductive roller to which a voltage is applied to the photoconductor, and the toner image on the photoconductor is transferred to the transfer material. A copy image is obtained through a fixing process.
However, it has been found that the contact charging method or the contact transfer method has an alarming problem, unlike the case of using corona discharge.
[0039]
Specifically, first, in the case of the contact charging method, the charging member is pressed against the surface of the photoreceptor with a pressing pressure. For this reason, the presence of untransferred residual toner, ie, transfer residual toner, makes it difficult to maintain sufficient contact between the contact charging member and the photosensitive member, and the chargeability deteriorates. Transfer of toner, that is, fogging is likely to occur. Further, since toner accumulates on the charging member, the photosensitive member cannot be uniformly charged, resulting in a decrease in image density and a harshness. Further, since the charging member is pressed against the toner, toner fusing is likely to occur, and these tendencies become more pronounced as the amount of toner remaining after transfer increases.
[0040]
Next, in the case of the contact transfer method, the transfer member is brought into contact with the photoconductor through the transfer member at the time of transfer, so that the toner image is pressed against the transfer material when the toner image formed on the photoconductor is transferred to the transfer material. In other words, a problem of partial transfer failure called so-called transfer omission occurs. In addition, as a recent technology direction, there has been a demand for higher resolution and higher definition development methods, and in order to respond to these demands, progress is being made toward reducing the particle size of toner. Thus, as the toner particle size becomes smaller, the adhesion force of the toner particles to the photoreceptor (such as mirror image force and van der Waals force) becomes larger than the Coulomb force applied to the toner particles in the transfer process, resulting in a residual transfer. The toner increases, and the transfer defect tends to be further deteriorated. As described above, in the image forming method using the contact charging method and the contact transfer method which are very preferable in consideration of the environment, it is desired to develop a magnetic developer having high transferability, excellent charging stability, and hardly causing toner fusion. It is rare.
[0041]
[Problems to be solved by the invention]
An object of the present invention is to provide a toner that solves the above-mentioned problems of the prior art. That is, an object of the present invention is to provide a magnetic toner that is excellent in charge uniformity and fixability and can obtain a high-definition image, an image forming method using the toner, and a process cartridge.
Another object of the present invention is to provide a magnetic toner that is less likely to cause image defects even when used for a long time and has excellent transferability, an image forming method using the toner, and a process cartridge.
[0042]
[Means for Solving the Problems]
  The present invention relates to a magnetic toner having toner particles containing at least a binder resin component and iron oxide. I) Content of carbon element present on the surface of the toner particles measured by X-ray photoelectron spectroscopy (A ) The ratio (B / A) of the content (B) of the iron element to) is less than 0.001, ii) the projected area equivalent diameter of the magnetic toner is C, and a transmission electron microscope (TEM) is used.Observed at a magnification of 10,000 timesMagnetic toner breakageOn the faceIron oxide particle surface and toner particle surfaceWhenWhen the minimum value of the distance is D, the magnetic toner satisfying the relationship of D / C ≦ 0.02 is 50% by number or more, and iii) the average circularity of the magnetic toner is 0.970 or more, iv) In the molecular weight distribution measured by gel permeation chromatography (GPC) of the THF soluble content of the magnetic toner, there is a peak top of the main peak in the molecular weight range of 5000 to 50000, and X calculated from the following formula (1) Is 1.4 or less,
[0043]
[Expression 2]

V) Inorganic fine powder on toner particle surfaceAnd VI) the binder resin component contains at least a polymer obtained by polymerizing a monomer containing at least a styrene monomer using an organic peroxide.A magnetic toner, an image forming method using the toner, and a process cartridge.
[0044]
DETAILED DESCRIPTION OF THE INVENTION
<1> Magnetic toner of the present invention
The magnetic toner of the present invention has toner particles containing at least a binder resin component and iron oxide.
[0045]
As a result of intensive studies on the homogenization and stabilization of the charging of the magnetic toner so far, the present inventors have found that the content (A) of the carbon element present on the surface of the magnetic toner measured by X-ray photoelectron spectroscopy analysis. The ratio (B / A) of the iron element content (B) is less than 0.001, and the average circularity of the toner calculated from the circularity determined by the following formula (2) is 0.970 or more. It has been found that the present invention is extremely effective for the homogenization and stabilization of the charging property of the present invention.
[0046]
[Equation 3]

(Where L₀Indicates the perimeter of a circle having the same projected area as the particle image, and L indicates the perimeter of the projected image of the particle. )
In addition, by using the toner as described above, a cleaner-less structure in which a ghost image is likely to be generated due to poor toner collection, an image forming method combining contact charging, a contact charging step and a one-component non-contact development step and contact. Also in the image forming method including the transfer step, the photoconductor is scraped, charged and transfer defects are remarkably suppressed, and a high-definition image free from fog and other image defects can be stably obtained even after long-term use. And the present invention has been achieved.
[0047]
This is difficult to achieve with a magnetic toner using magnetic iron oxide that has been generally used.
[0048]
The reason is that the magnetic iron oxide used was not sufficiently and uniformly hydrophobized.
[0049]
When the magnetic toner is manufactured, the dispersibility of the magnetic iron oxide particles in the toner binder resin component can be improved by using the magnetic iron oxide having a hydrophobic surface. Even when a large amount of magnetic iron oxide is exposed on the surface of the toner particles, the charging performance of the toner is hardly impaired under any environment if the surface of the magnetic iron oxide is uniformly hydrophobized.
[0050]
Therefore, various methods for hydrophobizing the surface of magnetic iron oxide have been proposed. However, with the conventional methods, it is difficult to obtain magnetic iron oxide that has been sufficiently and uniformly hydrophobized. Also, when a large amount of treatment agent or the like is used, or when a highly viscous treatment agent or the like is used, the degree of hydrophobicity is certainly increased, but coalescence of particles occurs, and compatibility between hydrophobicity and dispersibility is not necessarily achieved. Not achieved.
[0051]
Generally, since the untreated iron oxide surface has hydrophilicity, it is necessary to hydrophobize the hydrophilic iron oxide in order to obtain hydrophobic iron oxide. The uniformity of the conversion is insufficient, and the conventional toner using such an iron oxide varies in chargeability depending on the humidity and the like and lacks stability.
[0052]
On the other hand, the iron oxide used as the magnetic material in the toner of the present invention has a very high level of hydrophobicity uniformity. Specifically, for example, when hydrophobizing iron oxide, an iron oxide obtained by surface treatment while hydrolyzing a coupling agent while dispersing iron oxide to have a primary particle size in an aqueous medium. is there. Compared with treatment in the gas phase, the hydrophobization method in an aqueous medium is less likely to cause coalescence between the iron oxide particles, and the repulsive action between the iron oxide particles due to the hydrophobization treatment works. Since the surface treatment is performed almost in the state of primary particles, highly uniform hydrophobicity is achieved.
[0053]
The method of treating the surface of iron oxide while hydrolyzing the coupling agent in an aqueous medium does not require the use of a coupling agent that generates a gas, such as chlorosilanes and silazanes. In the phase, the iron oxide particles can be easily combined with each other, and a highly viscous coupling agent which has been difficult to be treated can be used, so that the hydrophobizing effect is great.
Examples of the coupling agent that can be used in the present invention include a silane coupling agent and a titanium coupling agent. More preferably used is a silane coupling agent, which is represented by the following general formula (I).
[0054]
[Chemical 1]
R_mSiY_n  (I)
(In the formula, R represents an alkoxy group, m represents an integer of 1 to 3, Y represents a hydrocarbon group such as an alkyl group, vinyl group, glycidoxy group, and methacryl group, and n represents an integer of 1 to 3. (However, m + n = 4.)
Examples of the silane coupling agent represented by the general formula (I) include vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, methyltrimethoxysilane, and methyltriethoxy. Examples include silane, isobutyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, hydroxypropyltrimethoxysilane, phenyltrimethoxysilane, n-hexadecyltrimethoxysilane, and n-octadecyltrimethoxysilane. .
In particular, it is preferable to hydrophobize iron oxide in an aqueous medium using an alkyltrialkoxysilane coupling agent represented by the following general formula (II).
[0055]
[Chemical 2]
C_pH_{2p + 1}-Si- (OC_qH_{2q + 1})_Three
(In the formula, p represents an integer of 2 to 20, and q represents an integer of 1 to 3).
When p in the above formula is smaller than 2, the hydrophobization treatment is easy, but it may be difficult to sufficiently impart hydrophobicity. When p is larger than 20, the hydrophobicity is sufficient. The coalescence of iron oxide particles increases, and it may be difficult to sufficiently disperse the iron oxide particles in the toner.
[0056]
On the other hand, when q is larger than 3, the reactivity of the silane coupling agent is lowered and the hydrophobicity is not sufficiently performed.
[0057]
In particular, p in the formula represents an integer of 2 to 20 (more preferably an integer of 3 to 15), and q represents an integer of 1 to 3 (more preferably an integer of 1 or 2). A coupling agent should be used.
[0058]
The treatment amount is 0.05 to 20 parts by mass, preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of iron oxide.
[0059]
In the present invention, the aqueous medium is a medium containing water as a main component. Specific examples of the aqueous medium include water itself, water added with a small amount of a surfactant, water added with a pH adjusting agent, and water added with an organic solvent. As the surfactant, a nonionic surfactant such as polyvinyl alcohol is preferable. The surfactant is preferably added in an amount of 0.1 to 5% by mass with respect to water. Examples of the pH adjuster include inorganic acids such as hydrochloric acid.
[0060]
Stirring is sufficiently performed by, for example, a mixer having a stirring blade (specifically, a high shear force mixing device such as an attritor or a TK homomixer) so that the iron oxide particles become primary particles in the aqueous medium. Is good.
Since the surface of the iron oxide obtained in this way is uniformly hydrophobized, when used as a toner material, the dispersibility in the toner is very good and there is no exposure from the toner surface.
Therefore, by using such iron oxide, the ratio (B / A) of the content (B) of the iron element to the content (A) of the carbon element present on the surface of the toner measured by X-ray photoelectron spectroscopy analysis. ) Is less than 0.001, it is possible to obtain toner of the present invention, and uniformity and stabilization of charging of the toner can be achieved. By using this toner, high image quality and high durability stability can be achieved. Furthermore, by setting (B / A) to less than 0.0005, the chargeability and stability are further improved.
[0061]
Further, the iron oxide used as the magnetic material in the toner of the present invention may contain elements such as phosphorus, cobalt, nickel, copper, magnesium, manganese, aluminum, silicon, etc., and mainly contains iron trioxide and γ-iron oxide. These are used as components, and these may be used alone or in combination of two or more. These iron oxides preferably have a BET specific surface area of 2 to 30 m by the nitrogen adsorption method.²/ g, especially 3-28m²/ g and a Mohs hardness of 5 to 7 is preferred.
[0062]
The shape of iron oxide includes octahedrons, hexahedrons, spheres, needles, scales, etc., but those with low anisotropy such as octahedrons, hexahedrons, spheres, and irregular shapes increase the image density. Preferred above. Such a shape can be confirmed by SEM or the like.
As the particle size of iron oxide, in the particle size measurement for particles having a particle size of 0.03 μm or more, the volume average particle size is 0.1 to 0.3 μm, and particles having 0.03 to 0.1 μm are 40% by number or less. It is preferable that
[0063]
When an image is obtained from a magnetic toner using iron oxide having a volume average particle size of less than 0.1 μm, the color of the image shifts to reddish and the blackness of the image is insufficient, or the halftone image is more reddish. Generally, it is not preferable, such as a strong tendency to feel strongly. Further, since the surface area of iron oxide is increased, dispersibility is lowered, energy required for production is increased, and it is not efficient. Further, the effect of iron oxide as a colorant is weakened, and the image density may be insufficient, which is not preferable.
[0064]
On the other hand, when the volume average particle size of iron oxide exceeds 0.3 μm, the mass per particle increases, so the probability of exposure to the toner surface increases due to the influence of the specific gravity difference with the binder resin component during production, or production. This is not preferable because the possibility of significant wear of the apparatus increases and the sedimentation stability of the dispersion decreases.
[0065]
In addition, if the number of particles of 0.1 μm or less of the iron oxide exceeds 40% by number in the toner, the surface area of the iron oxide increases and the dispersibility decreases, and the toner tends to form agglomerates in the toner. The number is preferably 40% by number or less because the possibility that the colorability is impaired or the coloring power is lowered is increased. Furthermore, if it is 30% by number or less, the tendency is further reduced, and therefore, it is more preferable.
The magnetic properties of these iron oxides include a saturation magnetization of 10 to 200 Am under a magnetic field of 795.8 kA / m.²/ kg, residual magnetization 1 ~ 100Am²/ kg and a coercive force of 1 to 30 kA / m are used.
[0066]
In addition, the volume average particle diameter of iron oxide can be measured using a transmission electron microscope (TEM). Specifically, a powder sample of the toner to be measured is observed with a transmission electron microscope (TEM), and the diameter of 100 iron oxide particles in the field of view is measured to obtain the volume average particle diameter.
[0067]
As a specific observation method by the above-mentioned TEM, after sufficiently dispersing particles to be observed in a room temperature curable epoxy resin, a cured product obtained by curing in an atmosphere at a temperature of 40 ° C. for 2 days, The method of observing as a flaky sample with a microtome equipped with diamond teeth is exemplified.
[0068]
The specific surface area can be obtained by adsorbing nitrogen gas on the sample surface using a specific surface area measuring device Autosorb 1 (manufactured by Yuasa Ionics) according to the BET method and calculating the specific surface area using the BET multipoint method. .
The iron oxide used in the toner of the present invention is produced, for example, by the following method.
[0069]
An aqueous solution containing ferrous hydroxide is prepared by adding an alkali such as sodium hydroxide in an amount equivalent to or greater than the iron component to the ferrous sulfate aqueous solution. Air was blown in while maintaining the pH of the prepared aqueous solution at pH 7 or higher (preferably pH 8-10), and ferrous hydroxide was oxidized while heating the aqueous solution to 70 ° C. or higher. First, a seed crystal is formed.
[0070]
Next, an aqueous solution containing about 1 equivalent of ferrous sulfate is added to the slurry-like liquid containing seed crystals based on the amount of alkali added previously. While maintaining the pH of the liquid at 6 to 10, the reaction of ferrous hydroxide is promoted while blowing air, and the magnetic iron oxide particles are grown around the seed crystal. As the oxidation reaction proceeds, the pH of the liquid shifts to the acidic side, but the pH of the liquid is preferably not less than 6. Adjust the pH of the solution at the end of the oxidation reaction, stir well so that the magnetic iron oxide becomes primary particles, add the coupling agent, stir well, stir, filter, dry, and lightly crush after stirring By doing so, hydrophobized magnetic iron oxide particles can be obtained. Alternatively, after the oxidation reaction is completed, the iron oxide particles obtained by washing and filtering are redispersed in another aqueous medium without drying, and then the pH of the redispersion is adjusted and sufficiently stirred. A silane coupling agent may be added to perform the coupling treatment.
[0071]
In any case, it is important that the untreated iron oxide particles generated in the aqueous solution be hydrophobized in the state of the water-containing slurry before passing through the drying step. This is because if untreated iron oxide particles are dried as they are, coalescence between the particles cannot be avoided, and even if wet-hydrophobic treatment is performed on such agglomerated powder, uniform hydrophobization treatment is possible. This is because it is difficult to achieve B / A <0.001, which is a feature of the magnetic toner of the present invention, with a toner using such surface-treated iron oxide.
[0072]
As the ferrous salt, iron sulfate generally produced as a by-product in the production of sulfuric acid titanium, iron sulfate produced as a by-product with the surface cleaning of the steel sheet can be used, and iron chloride or the like can be used. The method for producing magnetic iron oxide by the aqueous solution method generally uses an iron concentration of 0.5 to 2 mol / liter from the viewpoint of preventing the viscosity from increasing during the reaction and the solubility of iron sulfate. Generally, the lower the iron sulfate concentration, the finer the particle size of the product. Further, in the reaction, the larger the amount of air and the lower the reaction temperature, the easier the atomization.
[0073]
By using the hydrophobized iron oxide particles thus produced for the toner, the toner of the present invention having excellent image characteristics and stability can be obtained.
[0074]
Japanese Patent Publication No. 60-3181 also discloses a method for producing a magnetic polymer toner containing magnetic fine particles whose surface is wet-treated with a silane coupling agent.
[0075]
However, Japanese Patent Publication No. 60-3181 discloses a wet surface treatment of a dry powdery untreated magnetic material with a silane coupling agent.
Since these untreated dry magnetic powders cannot avoid particle coalescence due to primary agglomeration during drying, it is difficult to make individual magnetic particles uniformly hydrophobic even if wet surface treatment is performed. . Therefore, even when a polymerized toner is produced using such a surface-treated magnetic material, it is difficult to achieve B / A <0.001, which is a characteristic of the toner according to the present invention.
[0076]
A relationship of D / C ≦ 0.02, where C is the equivalent diameter of the projected area of the toner, and D is the minimum distance between the iron oxide and the toner particle surface in the cross-sectional observation of the toner using a transmission electron microscope (TEM). It is also one of the characteristics of the toner of the present invention that the number of toners satisfying the condition is 50% or more.
[0077]
In the present invention, the number of toners satisfying the relationship of D / C ≦ 0.02 is 50% or more, preferably 65% or more, and more preferably 75% or more.
[0078]
When the number of toners satisfying the relationship of D / C ≦ 0.02 is less than 50%, no magnetic particles are present at least outside the boundary line of D / C = 0.02 in the majority of toners. Assuming that such particles are spherical, when one toner particle is the entire space, at least 11.5% of the space where no iron oxide exists is present on the surface of the toner particle. Actually, the iron oxide does not exist uniformly at the closest position so as to form an inner wall inside the toner particle, so that it is clear that it becomes 12% or more. In the toner composed of such particles, various problems as described above are likely to occur.
[0079]
In the present invention, as a specific method for measuring D / C by TEM, particles to be observed can be sufficiently dispersed in a room temperature curable epoxy resin and then cured in an atmosphere at a temperature of 40 ° C. for 2 days. The cured product is preferably observed as it is or as a flaky sample with a microtome equipped with diamond teeth after freezing.
[0080]
A specific method for determining the ratio of the number of toners is as follows.
For the toner for determining D / C by TEM, the equivalent circle diameter is obtained from the cross-sectional area in the micrograph, and the value is a width of ± 10% of the number average particle diameter obtained by the method described later using a Coulter counter. Measure the minimum value (D) of the distance between the iron oxide particle surface and the toner particle surface for 100 corresponding toners, and determine the D / C, and the D / C value is 0.02 or less. Calculate the percentage of particles. The microphotograph at this time is preferably a magnification of 1 to 20,000 times in order to perform measurement with high accuracy. In the present invention, for example, a transmission electron microscope (H-600 type manufactured by Hitachi) is used as an apparatus, and observed at an accelerating voltage of 100 kV, and observed and measured using a microphotograph having a magnification of 10,000 times.
[0081]
A magnetic toner in which the number of toners satisfying the relationship of B / A <0.001 and satisfying the relationship of D / C ≦ 0.02 is 50% or more is different from that in which iron oxide is localized on the toner surface, and vice versa. The iron oxide is not uniformly dispersed in the toner, but the iron oxide is substantially uniformly dispersed in the magnetic toner, and the exposure of the iron oxide to the toner particle surface is suppressed. Magnetic toner. When the dispersion state of iron oxide is not uniform, it is difficult to satisfy the provisions of the present invention. In addition, if a magnetic toner in which iron oxide is hardly exposed on the surface of the toner particles is used, an electrostatic charge can be obtained even in an image forming method in which the magnetic toner is pressed against the surface of the electrostatic image carrier by a charging member or a transfer member. The surface of the image carrier is hardly scraped off, and the electrostatic charge image carrier scraping and toner fusion can be significantly reduced over a long period of time.
[0082]
The iron oxide used in the magnetic toner of the present invention is preferably used in an amount of 10 to 200 parts by weight, more preferably 20 to 180 parts by weight, based on 100 parts by weight of the binder resin component. When the blending amount of iron oxide is less than 10 parts by mass, the coloring power of the magnetic toner is poor, and it is difficult to suppress fogging. Not only does this decrease and it becomes difficult to uniformly disperse iron oxide into individual toner particles, but also the fixability will decrease.
[0083]
Next, the circularity of the toner, which is another feature of the present invention, will be described. In order to reduce the toner adhesion to the non-image area on the electrostatic image bearing member and the amount of residual toner, it is necessary that the chargeability of the toner particles is sufficient and uniform. Furthermore, when using a toner having a small particle diameter from the viewpoint of improving the image quality, the adhesion force of the toner particles increases, so the shape of the toner particles has a great influence on the toner adhesion to the non-image area on the electrostatic charge image carrier. Effect. In other words, the closer the toner particles are to a spherical shape and the more uniform the shape, the smaller the adhesion area of the particles, the less toner adhesion to the non-image area on the electrostatic image bearing member and the residual toner transfer amount, high image quality and durability Stability is achieved.
In addition, the toner particles according to the present invention are sufficiently charged, and as described above, the adhesion of the toner particles is reduced, so that the toner particles from the electrostatic charge image carrier to the transfer material such as paper can be transferred. Transfer efficiency is also greatly improved. This can be said to be an important toner performance for achieving high resolution as well as reproducibility of a minute dot image.
[0084]
Therefore, since the residual toner after transfer is greatly reduced by using such a magnetic toner, the amount of toner present in the pressure contact portion between the charging member and the photosensitive member is very small, and even in an image forming method having a contact charging step. It is considered that the photoconductor scraping and toner fusion are prevented, and image defects are remarkably suppressed. Further, since the toner having an average circularity of 0.970 or more has almost no edge portion on the surface, the surface of the photosensitive member is not scratched at the pressure contact portion between the charging member and the photosensitive member, and therefore the surface of the photosensitive member is prevented from being scraped. It can also be mentioned.
[0085]
These effects are conspicuous even in an image forming method including a contact transfer process in which transfer loss tends to occur.
The magnetic toner of the present invention may have a weight average particle diameter of 3 to 10 μm, more preferably less than 4 to 8 μm, in order to faithfully develop finer latent image dots for higher image quality. preferable. In a magnetic toner having a weight average particle size of less than 3 μm, the transfer residual toner on the photoconductor increases due to a decrease in transfer efficiency, making it difficult to maintain the uniformity of charging. Furthermore, in addition to an increase in the overall surface area of the magnetic toner, the fluidity and agitation as a powder decrease, and it becomes difficult to uniformly charge individual toner particles, so fog and transferability tend to deteriorate. This is not preferable for the magnetic toner used in the present invention because it tends to cause uneven image unevenness. When the weight average particle diameter of the toner exceeds 10 μm, the characters and line images are likely to scatter and it is difficult to obtain high resolution. Furthermore, as the apparatus becomes higher in resolution, toner of 8 μm or more tends to deteriorate the reproduction of one dot.
The magnetic toner according to the present invention preferably has an endothermic peak at 40 to 110 ° C., more preferably 45 to 90 ° C. when the temperature is increased, in the DSC curve of the toner measured by a differential scanning calorimeter.
[0086]
A toner with a weight average particle diameter of 10 μm or less can obtain a very high-definition image, but toner particles with a small particle diameter enter the gaps in the paper fibers when a transfer material such as paper is used, Heat reception from the heat fixing roller is insufficient, and low temperature offset is likely to occur.
[0087]
However, if the toner is designed to have an endothermic peak in the range of 40 to 110 ° C. when the temperature is raised in the DSC curve of the toner measured by a differential scanning calorimeter, the photosensitivity is achieved while achieving both high resolution and offset resistance. It becomes possible to prevent the body from being scraped. More preferably, it has an endothermic peak in the range of 45 to 90 ° C. when the temperature is raised. When the endothermic peak of the magnetic toner is lower than 40 ° C., there may be a problem in storage stability and chargeability. When the endothermic peak is higher than 110 ° C., it becomes difficult to prevent the photoconductor from being scraped. There is a case.
[0088]
In the DSC curve of a toner measured by a differential scanning calorimeter, there are various methods for expressing an endothermic peak in the range of 40 to 110 ° C. at the time of temperature rise. This can be easily achieved by using a known wax component as part of the raw material.
[0089]
The magnetic toner of the present invention is preferably used by containing 0.5 to 50 parts by mass of a wax component with respect to 100 parts by mass of the binder resin component. If the content of the wax component is less than 0.5 parts by mass, the effect of suppressing the low temperature offset is poor, and if it exceeds 50 parts by mass, the long-term storage stability is lowered and the dispersibility of other toner materials is deteriorated, and the toner flow Leading to deterioration of image quality and image characteristics.
[0090]
Usually, a toner image is transferred onto a transfer material in a transfer process, and the toner image is then fixed on the transfer material with energy such as heat and pressure to obtain a semi-permanent image. As a fixing method at this time, a heat roll type fixing is generally used. However, as described above, if a toner having a weight average particle diameter of 10 μm or less can be used, a very high-definition image can be obtained. When a transfer material such as paper is used, toner particles having a small diameter enter a gap between paper fibers, and heat reception from the heat fixing roller becomes insufficient, so that low temperature offset is likely to occur. However, in the magnetic toner of the present invention, by containing an appropriate amount of the wax component as a release agent, it is possible to prevent the photoconductor from being scraped while achieving both high resolution and offset resistance.
[0091]
Examples of the wax component usable in the toner of the present invention include paraffin wax, microcrystalline wax, petroleum wax such as petrolactam and derivatives thereof, montan wax and derivatives thereof, hydrocarbon wax and derivatives thereof by Fischer-Tropsch method, and polyethylene. Polyolefin waxes and derivatives thereof, natural waxes such as carnauba wax and candelilla wax and derivatives thereof. Derivatives here include oxides, block copolymers with vinyl monomers, and graft modified products. Furthermore, higher fatty alcohols, fatty acids such as stearic acid and palmitic acid or compounds thereof, acid amide waxes, ester waxes, ketones, hydrogenated castor oil and derivatives thereof, plant waxes and animal waxes can also be used.
[0092]
Among these wax components, in the DSC curve in which the magnetic toner is measured by a differential scanning calorimeter, in order to have an endothermic peak in the region of 40 to 110 ° C. when the temperature rises, the wax component having the maximum endothermic peak in that range. Is preferably used, and a wax component having a maximum endothermic peak in the region of 45 to 90 ° C. is more preferably used. When the wax component has the maximum endothermic peak in the above temperature range, it is possible to effectively exhibit releasability while greatly contributing to low-temperature fixing. When the maximum endothermic peak is less than 40 ° C., the self-aggregation force of the wax component becomes weak, and as a result, the high temperature offset resistance is deteriorated. On the other hand, if the maximum endothermic peak exceeds 110 ° C., the fixing temperature becomes high and low temperature offset tends to occur, which is not preferable. Further, in the case where granulation / polymerization is carried out in an aqueous medium and a toner is directly obtained by the polymerization method, a high maximum endothermic peak temperature is not preferable because a problem such as precipitation of a wax component mainly occurs during granulation.
[0093]
The endothermic peak temperature of toner and wax is measured according to “ASTM D 3418-8”. For the measurement, for example, DSC-7 manufactured by PerkinElmer is used. The temperature correction of the device detection unit uses the melting points of indium and zinc, and the correction of heat uses the heat of fusion of indium. An aluminum pan is used as a measurement sample, an empty pan is set as a control, and measurement is performed at a heating rate of 10 ° C./min. Further, the glass transition temperature (Tg) of the binder resin component or the like can also be measured by the measuring device.
[0094]
The magnetic toner of the present invention has a toner magnetization strength of 10 to 50 Am at a magnetic field of 79.6 kA / m (1000 oersted).²/ kg (emu / g) is preferable. By providing magnetic force generating means in the developing device, magnetic toner can prevent leakage of the toner, and not only can the toner transportability or stirrability be improved, but also magnetic force can be applied to the toner carrier. By providing the generating means, it becomes easy to prevent the toner from scattering because the magnetic toner forms spikes. However, the magnetic strength of the toner at a magnetic field of 79.6 kA / m is 10 Am²If it is less than / kg, the above effects cannot be obtained, and if magnetic force is applied to the toner carrier, the rise of the toner becomes unstable, and fog and image density due to the fact that the toner cannot be uniformly charged. Image defects such as unevenness and poor collection of untransferred toner are likely to occur.
[0095]
The magnetic strength of the toner at a magnetic field of 79.6 kA / m is 50 Am.²If it is greater than / kg, when a magnetic force is applied to the toner, the fluidity of the toner is remarkably reduced due to magnetic aggregation, and fog and image stains are likely to occur due to a decrease in chargeability. In addition, the intensity of magnetization can be made into said range by adjusting content of the said iron oxide to be used.
Further, since the toner has a circularity of 0.970 or more as in the toner of the present invention, the rising of the toner on the toner carrier becomes fine and dense, so that the charge is made uniform and the fog is further reduced.
In the present invention, the magnetization intensity of the magnetic toner is measured using a vibration magnetometer VSM P-1-10 (manufactured by Toei Kogyo Co., Ltd.) at a room temperature of 25 ° C. and an external magnetic field of 79.6 kA / m. The magnetic properties of the iron oxide are measured at an external magnetic field of 796 kA / m at room temperature of 25 ° C.
[0096]
The magnetic toner of the present invention has a main peak in the molecular weight range of 5000 to 50000 in the molecular weight distribution measured by gel permeation chromatography (GPC) of the THF soluble content of the magnetic toner.Peak topMore preferably, it is in the range of 8000 to 40000. When the peak top is less than 5000, when toner particles are produced by polymerization, the viscosity increase of the droplets during polymerization is very small, and the hydrophobized iron oxide tends to be unevenly distributed near the surface of the toner particles. , (B / A) may be difficult to be less than 0.001. In addition, there is a problem in the storage stability of the toner, and the toner deteriorates remarkably when a large number of sheets are printed out. On the other hand, if the peak top exceeds 50,000, there is a problem in low-temperature fixability, and when the toner particles are produced by polymerization, the dispersibility of the hydrophobized iron oxide due to a sharp rise in droplet viscosity during polymerization Tend to get worse. Moreover, it becomes difficult to set the circularity to 0.970 or more.
[0097]
The main peak having a peak top in the molecular weight range of 5000 to 50000 should have an X calculated by the following formula (1) of 1.4 or less, particularly preferably a main peak having a peak top in the molecular weight range of 8000 to 40000. And X is 1.1 or less.
[0098]
[Expression 4]

The elution times (sec) for molecular weights of 10000 and 100,000 are calculated by calculating a calibration curve using standard polystyrene, which will be described later, and entering 10000 and 100,000 in the term of molecular weight in the mathematical formula of the calibration curve. It's about time.
[0099]
In the pulverized toner, there is a conventional method in which a high molecular weight component having an effect on high temperature offset resistance is generated by kneading a binder resin component containing an insoluble component (crosslinking component). As described above, the polymer formed by kneading the molecular chain by kneading naturally has a wide molecular weight distribution, and it generates a large amount of intermediate molecular weight components that do not contribute much to high temperature offset resistance and inhibit low temperature fixability. In some cases, an ultra-low molecular weight component may be generated due to excessive cutting during kneading, and toner fusion to a photoreceptor or a sleeve may become a problem. Further, in the case of a conventional polymerization toner, it is possible to generate a THF-insoluble component by polymerizing a composition comprising a colorant, a monomer, etc. in the presence of a crosslinking agent. Unlike the suspension polymerization method, the molecular weight distribution of the binder resin component to be generated is essentially widened. Therefore, it is difficult to sharpen the molecular weight distribution of the component soluble in THF by the conventional technique.
[0100]
As a result of intensive studies on how to sharpen the molecular weight distribution of THF-soluble matter while producing an appropriate amount of THF-insoluble matter, the present inventors have found that specific raw materials can be obtained under specific polymerization conditions. By combining them, an insoluble matter effective for high temperature offset resistance is generated, the X is kept below 1.4, and the peak top of the main peak is kept within a predetermined molecular weight range to maintain the high temperature offset resistance. On the other hand, it was found that the low-temperature fixability was excellent and the charging uniformity was extremely good.
[0101]
As long as the value of X is 1.4 or less, the main peak does not adversely affect the effect of the present invention even if the main peak is slightly lowered on the high molecular weight side and low molecular weight side, but the molecular weight distribution measured by GPC. In the binder resin component, the component having a molecular weight of 300,000 or more is less than 20% by area, more preferably less than 10% by area, and the component having a molecular weight of 2000 to 5000 is less than 15% by area, more preferably The effect of this invention is further exhibited as it is less than 10 area%.
[0102]
The production method suitably used for obtaining the magnetic toner of the present invention will be described later. For example, in the case of the polymerization method, highly surface-treated iron oxide, wax component, cross-linking agent, α-methylstyrene dimer, etc. It can be easily obtained by granulating a monomer composition containing the above chain transfer agent in an aqueous medium and subjecting it to suspension polymerization using an organic peroxide as a polymerization initiator.
[0103]
The molecular weight of the component derived from the binder resin component soluble in THF by GPC may be measured as follows.
[0104]
A solution obtained by allowing the toner to stand still in THF at room temperature for 24 hours is filtered through a solvent-resistant membrane filter having a pore diameter of 0.2 μm to obtain a sample solution, which is measured under the following conditions. In addition, sample preparation adjusts the quantity of THF so that the density | concentration of the component soluble in THF may be 0.4-0.6 mass%.
[0105]
Equipment: High-speed GPC HLC8120 GPC (manufactured by Tosoh Corporation)
Column: Shodex KF-801, 802, 803, 804, 805, 806, 807, 7 stations (Showa Denko)
Eluent: THF
Flow rate: 1.0ml / min
Oven temperature: 40.0 ℃
Sample injection volume: 0.10ml
When calculating the molecular weight of the sample, standard polystyrene resin (TSO Standard Polystyrene F-850, F-450, F-288, F-128, F-80, F-40, F-20, F- 10, F-4, F-2, F-1, A-5000, A-2500, A-1000, A-500) are used.
[0106]
Further, the magnetic toner of the present invention preferably contains an appropriate amount of THF-insoluble matter (crosslinking component of the binder resin), and the amount thereof is present in the molecular weight distribution of the THF-soluble component, particularly the proportion of the high-molecular weight component. Depending on whether or not it is, it is usually 1 to 60% by mass, preferably 5 to 40% by mass based on the binder resin component. The THF insoluble matter is measured as follows.
[0107]
Toner particles or 1 g of toner is precisely weighed and charged into a cylindrical filter paper, and Soxhlet extracted with 200 ml of THF for 20 hours. Thereafter, the cylindrical filter paper is taken out, vacuum dried at 40 ° C. for 20 hours, and the residue weight is measured to calculate. At this time, since the toner contains components other than the binder resin component such as iron oxide, charge control agent, wax component, and external additive, these contents and these are soluble or insoluble in THF. In view of the above, the THF-insoluble matter based on the binder resin component is calculated. If a component soluble in the toner other than the binder resin component and a component soluble in THF (eg, wax soluble in THF) is used, the content of that component is calculated separately, It is converted to how much of the binder resin component is insoluble in THF.
[0108]
The binder resin component, which is a constituent material of the magnetic toner of the present invention, is preferably mainly composed of a styrene resin because the molecular weight distribution can be controlled relatively easily. The styrene-based resin is obtained by polymerizing a monomer containing styrene using a polymerization initiator. That is, it can be obtained by copolymerizing a styrene monomer and another polymerizable monomer.
[0109]
Other polymerizable monomers that can be used are not particularly limited. For example, styrene series such as o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, and p-ethylstyrene. Monomer: methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, acrylic acid Acrylic esters such as 2-chloroethyl and phenyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, methacrylic acid 2-ethylhexyl, methacryl Stearyl, phenyl methacrylate, dimethylaminoethyl methacrylate, methacrylic acid esters such as diethylaminoethyl methacrylate; and other acrylonitrile, methacrylonitrile, and the like monomers acrylamide. These resins are used alone or generally so that the theoretical glass transition temperature (Tg) described in the publication Polymer Handbook 2nd edition III-p139-192 (John Wiley & Sons) is 40-70 ° C. Monomers are appropriately mixed and used. If the theoretical glass transition temperature is less than 40 ° C., problems are likely to occur from the viewpoint of storage stability and durability stability of the toner, while if it exceeds 70 ° C., problems may occur in the toner fixability.
[0110]
Examples of the polymerization initiator used in the present invention include conventionally known azo polymerization initiators and organic peroxide polymerization initiators. As the azo polymerization initiator, 2,2′-azobis- (2 , 4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis-4-methoxy-2,4- Examples thereof include dimethylvaleronitrile and azobisisobutyronitrile. Examples of the organic peroxide polymerization initiator include t-butyl peroxyacetate, t-butyl peroxylaurate, t-butyl peroxypivalate, t- Butyl peroxy-2-ethylhexanoate, t-butyl peroxyisobutyrate, t-butyl peroxyneodecanoate, t-hexyl peroxyacetate, t -Hexylperoxylaurate, t-hexylperoxypivalate, t-hexylperoxy-2-ethylhexanoate, t-hexylperoxyisobutyrate, t-hexylperoxyneodecanoate, t-butyl Peroxybenzoate, α, α′-bis (neodecanoylperoxy) diisopropylbenzene, cumylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, 1 , 1,3,3-tetramethylbutylperoxyneodecanoate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, 2,5-dimethyl-2,5-bis (2-ethylhexanoylper) Oxy) hexane, 1-cyclohexyl-1-methylethylperoxy-2-ethylhexano Tate, t-hexyl peroxyisopropyl monocarbonate, t-butyl peroxyisopropyl monocarbonate, t-butyl peroxy 2-ethylhexyl monocarbonate, t-hexyl peroxybenzoate, 2,5-dimethyl-2,5-bis (Benzoylperoxy) hexane, t-butylperoxy-m-toluoylbenzoate, bis (t-butylperoxy) isophthalate, t-butylperoxymaleic acid, t-butylperoxy-3,5,5 -Peroxyesters such as trimethylhexanoate, 2,5-dimethyl-2,5-bis (m-toluoylperoxy) hexane; diacyl peroxides such as benzoyl peroxide, lauroyl peroxide, isobutyryl peroxide; Diisop Peroxydicarbonate such as propyl peroxydicarbonate, bis (4-t-butylcyclohexyl) peroxydicarbonate, 1,1-di-t-butylperoxycyclohexane, 1,1-di-t-hexylperoxy Peroxyketals such as cyclohexane, 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, 2,2-di-t-butylperoxybutane; di-t-butyl peroxide, dioctyl Dialkyl peroxides such as milperoxide and t-butylcumyl peroxide; t-butylperoxyallyl monocarbonate and the like can be mentioned as others, and two or more of these initiators can be used as necessary.
[0111]
Among the above-mentioned polymerization initiators, organic peroxide polymerization initiators, in particular, tend to generate a THF-insoluble matter and reduce intermediate molecular weight components because hydrogen abstraction (crosslinking) reaction occurs together with the polymerization reaction. And is preferably used because the toner of the present invention is easily obtained. Of these organic peroxide-based polymerization initiators, peroxyesters, peroxydicarbonates, and diacyl peroxides are preferably used. Among them, when diacyl peroxide is used, the main peak of THF-soluble matter is particularly high. Since it becomes sharp, the uniform chargeability is further improved, which is preferable.
[0112]
The polymerization initiator used in the present invention is preferably used in an amount of 0.2 to 20 parts by mass with respect to 100 parts by mass of the monomer. When the polymerization reaction is carried out with the added amount, a main peak is observed between the molecular weights of 5000 to 50000. A polymer having the desired strength and suitable melting characteristics.
[0113]
In addition, when an organic peroxide polymerization initiator is used in the present invention, the theoretically active oxygen amount is desirably in the range of 3.0 to 12.0%, and if it is less than 3.0%, a large amount of polymerization initiator is used. This is economically disadvantageous, and if it exceeds 12.0%, it may be difficult to handle and control the polymerization reaction.
[0114]
In the present invention, in order to control the amount of THF-insoluble matter and sharpen the main peak of the binder resin component soluble in THF, radical polymerization is performed by adding a conventionally known chain transfer agent to the monomer composition. Is preferred.
[0115]
Examples of the chain transfer agent that can be used in this case include α-methylstyrene dimer, t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, carbon tetrachloride, carbon tetrabromide and the like. Of these, α-methylstyrene dimer, t-dodecyl mercaptan, and n-dodecyl mercaptan are more preferably used. The α-methylstyrene dimer can make the value of X smaller than thiols such as t-dodecyl mercaptan and is particularly preferably used. These chain transfer agents can be added before the start of polymerization or during the polymerization. These chain transfer agents are generally used in a proportion of 0.01 to 10 parts by mass, preferably 0.1 to 5 parts by mass, with respect to 100 parts by mass of the monomer.
[0116]
When producing the polymerized toner according to the present invention, a crosslinking agent should be added to the monomer composition in order to control the molecular weight distribution of the binder resin component soluble in THF and the content of THF insoluble matter. The preferred addition amount is 0.001 to 15% by mass with respect to the monomer.
[0117]
Here, the crosslinking agent is not particularly limited as long as it is a compound having two or more polymerizable double bonds in one molecule. For example, divinylbenzene, divinylnaphthalene, ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1 , 3-butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, diallyl ether, pentaerythritol triacrylate, triallyl ether, divinylaniline, divinyl ether, divinyl sulfide, divinyl sulfone, etc. Crosslinkable polymers such as low molecular crosslinking agents having a plurality of polymerizable double bonds, unsaturated polyesters, styrene-butadiene copolymers, etc. Ku can be used as a mixture.
[0118]
The toner of the present invention can be manufactured by a pulverization method, but in the pulverization method, it is necessary to perform mechanical, thermal, or some special treatment in order to set the average circularity of the toner to 0.970 or more. Therefore, it is preferable to produce by suspension polymerization. Even when a toner is produced by suspension polymerization using a normal magnetic material, the magnetic material is inferior in dispersibility, so that the magnetic material is unevenly distributed on the toner surface, or the magnetic material is confused during granulation in an aqueous medium. However, it is difficult to obtain a toner having an average circularity of 0.970 or more because the particle shape is distorted by being dragged by the iron oxide. However, the iron oxide used in the present invention has a uniform level at a high level. Since the hydrophobicity is performed, a toner having an average circularity of 0.970 or more can be easily obtained.
[0119]
In this invention, you may superpose | polymerize by adding resin to a monomer composition. For example, hydrophilic functional groups such as amino groups, carboxylic acid groups, hydroxyl groups, sulfonic acid groups, glycidyl groups, and nitrile groups that cannot be used because monomers are water-soluble and dissolve in aqueous suspension to cause emulsion polymerization. When it is desired to introduce the monomer component contained in the toner, a random copolymer of these and a vinyl compound such as styrene or ethylene, a block copolymer, or a copolymer such as a graft copolymer, Alternatively, it can be used in the form of a polycondensate such as polyester or polyamide, or a polyaddition polymer such as polyether or polyimine.
[0120]
When such a polymer containing a polar functional group is allowed to coexist in the toner, the above-mentioned wax component is phase-separated and the encapsulation becomes stronger, and a toner having good offset resistance, blocking resistance, and low-temperature fixability can be obtained. Obtainable.
As the usage-amount of the said resin, 1-20 mass parts is preferable with respect to 100 mass parts of polymerizable monomers. If the amount used is less than 1 part by mass, the effect of addition is small, whereas if it is used in excess of 20 parts by mass, it becomes difficult to design various physical properties of the polymerized toner. Further, the average molecular weight of the polymer containing these polar functional groups is preferably 3000 or more. When the molecular weight is less than 3000, particularly 2000 or less, the present polymer tends to concentrate near the surface, which is not preferable because it tends to adversely affect developability and blocking resistance. In addition, if a polymer having a molecular weight different from the molecular weight range of the toner obtained by polymerizing the monomer is dissolved in the monomer and polymerized, a toner having a wide molecular weight distribution and high offset resistance can be obtained. it can.
[0121]
The toner of the present invention may contain a charge control agent in order to stabilize the charge characteristics. As the charge control agent, known ones can be used, but a charge control agent that has a high charging speed and can stably maintain a constant charge amount is particularly preferable.
Further, when the toner is produced using a direct polymerization method, a charge control agent having a low polymerization inhibitory property and substantially free from a solubilized product in an aqueous dispersion medium is particularly preferable. Specific compounds include, as negative charge control agents, metal compounds of aromatic carboxylic acids such as salicylic acid, alkylsalicylic acid, dialkylsalicylic acid, naphthoic acid and dicarboxylic acid, metal salts or metal complexes of azo dyes or azo pigments, sulfones Examples thereof include a polymer compound having an acid or carboxylic acid group in the side chain, a boron compound, a urea compound, a silicon compound, and a calixarene. Examples of the positive charge control agent include a quaternary ammonium salt, a polymer compound having the quaternary ammonium salt in the side chain, a guanidine compound, a nigrosine compound, and an imidazole compound.
[0122]
These charge control agents are preferably used in an amount of 0.5 to 10 parts by mass with respect to 100 parts by mass of the polymerizable monomer. However, in the magnetic toner of the present invention, it is not essential to add a charge control agent, and the charge control agent is not necessarily contained in the toner by actively utilizing frictional charging with the layer pressure regulating member of the magnetic toner or the toner carrier. It is not necessary to include.
[0123]
Furthermore, other colorants may be used in combination with iron oxide. Examples of coloring materials that can be used in combination include magnetic or nonmagnetic inorganic compounds, and known dyes and pigments. Specifically, for example, ferromagnetic metal particles such as cobalt and nickel, or alloys obtained by adding chromium, manganese, copper, zinc, aluminum, rare earth elements to these, hematite, titanium black, nigrosine dye / pigment, carbon black, Examples include phthalocyanine. These may also be used after hydrophobizing the surface in the same manner as iron oxide.
[0124]
In the production of a magnetic toner by suspension polymerization, generally the above-described toner composition, that is, a polymerizable monomer, contains iron oxide, a colorant, a release agent, a plasticizer, a binder resin, a charge control agent, and a crosslinking agent. In addition, components necessary for the toner such as a chain transfer agent and other additives, for example, an organic solvent to be added to reduce the viscosity of the polymer produced by the polymerization reaction, a dispersant, etc. are appropriately added, and a homogenizer, ball mill, colloid mill, A monomer composition uniformly dissolved or dispersed by a dispersing machine such as an ultrasonic dispersing machine is suspended in an aqueous medium containing a dispersion stabilizer.
[0125]
At this time, the particle size of the obtained toner particles becomes sharper by using a high-speed disperser such as a high-speed stirrer or an ultrasonic disperser to obtain a desired toner particle size at a stretch. The polymerization initiator may be added at the same time when other additives are added to the polymerizable monomer, or may be mixed immediately before being suspended in the aqueous medium. Also, a polymerization initiator dissolved in a polymerizable monomer or solvent can be added immediately after granulation and before starting the polymerization reaction.
[0126]
After granulation, stirring may be performed using a normal stirrer to such an extent that the particle state is maintained and toner particles are prevented from floating and settling.
[0127]
In the suspension polymerization method of the present invention, known surfactants and organic / inorganic dispersants can be used as dispersion stabilizers. Among them, the inorganic dispersants hardly generate ultrafine powders that cause image defects, and their steric hindrance. Since dispersion stability is obtained by this, stability is not easily lost even when the reaction temperature is changed, and washing is easy and it is difficult to adversely affect the toner, so that it can be preferably used. Examples of such inorganic dispersants include polyvalent metal phosphates such as calcium phosphate, magnesium phosphate, aluminum phosphate and zinc phosphate; carbonates such as calcium carbonate and magnesium carbonate; calcium metasuccinate, calcium sulfate and barium sulfate. Inorganic salts: Inorganic oxides such as calcium hydroxide, magnesium hydroxide, aluminum hydroxide, silica, bentonite, and alumina can be used. These inorganic dispersants are preferably used in an amount of 0.2 to 20 parts by mass alone or in combination of two or more with respect to 100 parts by mass of the polymerizable monomer. In the case of aiming at a finer toner such as a toner having a weight average particle diameter of 5 μm or less, 0.001 to 0.1 parts by mass of a surfactant may be used in combination.
[0128]
Examples of the surfactant include sodium dodecylbenzene sulfate, sodium tetradecyl sulfate, sodium pentadecyl sulfate, sodium octyl sulfate, sodium oleate, sodium laurate, sodium stearate, and potassium stearate.
[0129]
When these inorganic dispersants are used, they may be used as they are, but in order to obtain finer particles, the inorganic dispersant particles can be generated in an aqueous medium. For example, in the case of calcium phosphate, a sodium phosphate aqueous solution and a calcium chloride aqueous solution can be mixed with high-speed stirring to produce water-insoluble calcium phosphate, which enables more uniform and fine dispersion.
At the same time, a water-soluble sodium chloride salt is produced as a by-product. However, if a water-soluble salt is present in the aqueous medium, dissolution of the polymerizable monomer in water is suppressed, and an ultrafine toner based on emulsion polymerization is produced. Since it becomes difficult to generate | occur | produce, it is more convenient. Since it becomes an obstacle when removing the remaining polymerizable monomer at the end of the polymerization reaction, it is better to replace the aqueous medium or desalinate with an ion exchange resin. The inorganic dispersant can be almost completely removed by dissolving with an acid or alkali after completion of the polymerization.
[0130]
In the polymerization step, the polymerization is performed at a polymerization temperature of 40 ° C. or higher, generally 50 to 90 ° C. When the polymerization is carried out in this temperature range, the wax component and the like to be sealed inside are precipitated by phase separation, and the encapsulation becomes more complete.
In order to consume the remaining polymerizable monomer, it is possible to raise the reaction temperature to 90 to 150 ° C. at the end of the polymerization reaction.
[0131]
The toner of the present invention has an inorganic fine powder on the surface of the toner particles. By allowing the inorganic fine powder to be present on the surface of the toner particles of the present invention, not only the fluidity of the toner can be improved, but also the charging property can be further stabilized. Examples of the inorganic fine powder include silica fine powder, titanium oxide fine powder, alumina fine powder and the like, or composite oxides thereof, and these are hydrophobized if necessary. Among these, it is preferable to use silica fine powder, particularly silica fine powder that has been subjected to a hydrophobic treatment.
[0132]
The inorganic fine powder used in the magnetic toner of the present invention has a number primary average particle size of 4 to 80 nm and a specific surface area of 30 m by nitrogen adsorption measured by the BET method.²/ g or more, especially 50-400m²Those in the range of / g are preferable because good results can be obtained. The specific surface area is measured in the same manner as iron oxide.
[0133]
In the present invention, the method for measuring the number primary average particle size of the inorganic fine powder is a photograph of the toner magnified by a scanning electron microscope, and the inorganic fine powder by an elemental analysis means such as XMA attached to the scanning electron microscope. Measure 100 or more primary particles of inorganic fine powder adhering to or liberating from the toner surface while comparing photographs of the toner mapped with the elements contained in the toner, and determine the primary average particle size. I can do it.
[0134]
As the silica fine powder used in the present invention, both a so-called dry method produced by vapor phase oxidation of a silicon halogen compound or a so-called wet silica produced from water glass or the like, or dry silica called fumed silica can be used. However, dry silica that has few silanol groups on the surface and inside and no production residue is preferably used.
Further, the silica fine powder used in the present invention is preferably hydrophobized.
[0135]
Examples of silane coupling agents used for hydrophobizing treatment include hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, and allylphenyldichlorosilane. , Benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilane mercaptan, trimethylsilyl mercaptan, triorganosilyl acrylate, vinyldimethylacetoxysilane, Dimethylethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilane, hexamethyldisiloxane, 1,3-divinyl Examples thereof include tetramethyldisiloxane and 1,3-diphenyltetramethyldisiloxane. Examples of the organosilicon compound include silicone oil.
[0136]
As a preferable silicone oil, the viscosity at 25 ° C. is about 30 to 1,000 mm.²For example, dimethyl silicone oil, methylphenyl silicone oil, α-methylstyrene modified silicone oil, chlorophenyl silicone oil, and fluorine modified silicone oil are preferable.
[0137]
Silicone oil treatment can be performed by, for example, mixing silica fine powder treated with a silane coupling agent and silicone oil directly using a mixer such as a Henschel mixer, or injecting silicone oil onto the base silica. Depending on how you do it. Alternatively, the silicone oil may be dissolved or dispersed in an appropriate solvent, and then mixed with the base silica fine powder to remove the solvent.
[0138]
If necessary, an external additive other than the fluidity improver may be added to the magnetic toner of the present invention.
[0139]
For example, the primary particle size exceeds 30 nm for the purpose of improving cleaning properties (preferably the BET specific surface area is 50 m).²/ g) fine particles, more preferably a primary particle size of 50 nm or more (preferably a BET specific surface area of 30 m)²It is also one of preferable modes to add inorganic fine particles or organic fine particles that are nearly spherical at less than / g). For example, spherical silica particles, spherical polymethylsilsesquioxane particles, and spherical resin particles are preferably used.
[0140]
Furthermore, other additives such as lubricant powders such as Teflon powder, zinc stearate powder and polyvinylidene fluoride powder; abrasives such as cerium oxide powder, silicon carbide powder and strontium titanate powder; anti-caking agent; carbon black powder, oxidation A small amount of conductivity imparting agents such as zinc powder and tin oxide powder; developability improvers for organic particles having opposite polarity, inorganic particles and the like can also be added. These additives are also preferably used after hydrophobizing the surface.
[0141]
The above-mentioned additive is preferably used in an amount of 0.1 to 5 parts by mass (preferably 0.1 to 3 parts by mass) with respect to 100 parts by mass of the magnetic toner.
[0142]
When the toner of the present invention is produced by a pulverization method, a known method can be used. Known methods include, for example, binder resins described later, iron oxide, wax components, charge control agents, and components necessary as toners such as colorants and other additives, such as Henschel mixers and ball mills. After thoroughly mixing in the mixer, melt and knead using a heat kneader such as a heating roll, kneader, extruder, etc., and other toner materials such as iron oxide are mixed into the resin. After being dispersed or dissolved, cooled, solidified, and pulverized, classified and subjected to surface treatment as necessary to obtain toner particles, and if necessary, a magnetic toner can be obtained by adding and mixing inorganic fine powder and the like. . Either the classification or the surface treatment may be performed first. In the classification step, it is preferable to use a multi-division classifier from the viewpoint of production efficiency.
The pulverization step can be performed using a known pulverizer such as a mechanical impact type or a jet type. In order to obtain a magnetic toner having a specific circularity according to the present invention, it is preferable to further heat and pulverize or to supplementarily apply a mechanical impact. Further, a hot water bath method in which finely pulverized (classified as necessary) toner particles are dispersed in hot water, a method of passing in a hot air stream, or the like may be used.
[0143]
As a method of applying a mechanical impact force, for example, there is a method using a mechanical impact type pulverizer such as a kryptron system manufactured by Kawasaki Heavy Industries, Ltd. or a turbo mill manufactured by Turbo Industry. Also, like devices such as Hosokawa Micron's Mechano-Fusion System and Nara Machinery's Hybridization System, the toner is pressed against the inside of the casing by centrifugal force with high-speed rotating blades, and the force of compression force, friction force, etc. A method of applying a mechanical impact force to the toner may be used.
[0144]
When processing with mechanical impact is applied, setting the ambient temperature during processing to a temperature near the glass transition point Tg of the toner (that is, a temperature in the range of ± 30 ° C. of the glass transition point Tg) prevents aggregation. From the viewpoint of productivity. More preferably, the treatment at a temperature in the range of ± 20 ° C. of the glass transition point Tg of the toner is particularly effective for improving the transfer efficiency.
[0145]
Furthermore, the toner of the present invention is a method for obtaining a spherical toner by atomizing a molten mixture into air using a disk or a multi-fluid nozzle described in Japanese Patent Publication No. 56-13945, etc. Represented by a dispersion polymerization method in which a toner is directly produced using an aqueous organic solvent in which the polymer obtained in 1 is insoluble, or a soap-free polymerization method in which a toner is produced by direct polymerization in the presence of a water-soluble polar polymerization initiator. The toner can also be produced by a method of producing toner using an emulsion polymerization method or the like.
[0146]
As the binder resin when the toner of the present invention is produced by a pulverization method, styrene such as polystyrene and polyvinyltoluene and a homopolymer of a substituted product thereof; styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene -Vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-dimethylaminoethyl acrylate Copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-dimethylaminoethyl methacrylate copolymer, styrene-vinyl methyl ether Copolymer, styrene-vinyl ethyl ether Styrene copolymers such as copolymers, styrene-vinyl methyl ketone copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-maleic acid copolymers, styrene-maleic acid ester copolymers ; Polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyethylene, polypropylene, polyvinyl butyral, silicone resin, polyester resin, polyamide resin, epoxy resin, polyacrylic acid resin, rosin, modified rosin, temper resin, phenol resin, aliphatic Alternatively, alicyclic hydrocarbon resins, aromatic petroleum resins, paraffin wax, carnauba wax and the like can be used alone or in combination. In particular, a styrene copolymer and a polyester resin are preferable in terms of development characteristics, fixing properties, and the like.
<2> Image forming method using magnetic toner of the present invention
The image forming method of the present invention includes a charging step, an electrostatic latent image forming step, a developing step, and a transfer step, and uses the magnetic toner of the present invention as a toner.
[0147]
Hereinafter, embodiments of the image forming method of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.
In FIG. 1, a charging roller 117 as a contact charging member, a developing device 140 as a developing unit, a transfer roller 114 as a transfer unit, a cleaner 116, a register roller 124, and the like are provided around a photosensitive drum 100 as an image carrier. It has been. The photosensitive drum 100 is charged to −700 V by the charging roller 117. (Applied voltage is AC voltage -2.0 kVpp (Vpp: potential between peaks), DC voltage -700 Vdc), and exposure is performed by irradiating the photosensitive drum 100 with the laser beam 123 by the laser generator 121. The electrostatic latent image on the photosensitive drum 100 is developed with a one-component magnetic toner by the developing device 140 and is transferred onto the transfer material by the transfer roller 114 in contact with the photosensitive drum via the transfer material. The transfer material P on which the toner image is placed is transported to the fixing device 126 by the transport belt 125 or the like and fixed on the transfer material P.
In addition, toner partially remaining on the photosensitive drum is cleaned by a cleaner 116 as a cleaning unit. As shown in FIG. 2, the developing device 140 is provided with a cylindrical toner carrier 102 (hereinafter also referred to as “developing sleeve”) made of a nonmagnetic metal such as aluminum or stainless steel in the vicinity of the photosensitive drum 100. The gap between the photosensitive drum 100 and the developing sleeve 102 is maintained at about 300 μm by a sleeve / photosensitive member gap holding member (not shown). This gap can be changed if necessary. A magnet roller 104 is fixed and disposed concentrically with the developing sleeve 102 in the developing sleeve 102. However, the developing sleeve 102 is rotatable. The magnet roller 104 is provided with a plurality of magnetic poles, as shown in the figure, where S1 influences development, N1 restricts the amount of toner coating, S2 takes in / conveys toner, and N2 affects toner blowout prevention.
[0148]
The toner is applied to the developing sleeve 102 and adhered and conveyed. An elastic blade 103 is provided as a toner layer thickness regulating member that regulates the amount of magnetic toner to be conveyed, and the amount of toner conveyed to the development region is controlled by the contact pressure of the elastic blade 103 against the developing sleeve 102. In the developing area, a developing bias having a DC voltage and an AC voltage is applied between the photosensitive drum 100 and the developing sleeve 102, and the toner on the developing sleeve 102 flies onto the photosensitive drum 100 in accordance with the electrostatic latent image and is visible. It becomes.
[0149]
As an example of the developing method using the toner of the present invention, a system in which the toner carrier and the electrostatic image carrier are not in contact will be described.
[0150]
In the non-contact developing method, magnetic toner is applied on the toner carrier at a thickness smaller than the closest distance (between S and D) between the toner carrier and the photoreceptor (electrostatic charge image carrier). Development is performed by applying an electric field. That is, the layer thickness regulating member for regulating the magnetic toner on the toner carrying member sets the toner layer thickness on the toner carrying member to be smaller than the closest gap between the photoreceptor and the toner carrying member. At this time, the layer thickness regulating member for regulating the magnetic toner on the toner carrying member is an elastic member, and it is particularly preferable from the viewpoint of uniformly charging the magnetic toner to be in contact with the toner carrying member via the toner.
[0151]
Further, it is preferable that the toner carrying member is disposed to face the photosensitive member with a separation distance of 100 to 1000 μm, and is preferably disposed to face the photosensitive member with a separation distance of 120 to 500 μm. preferable. If the separation distance of the toner carrier from the photosensitive member is smaller than 100 μm, the change in the development characteristics of the toner with respect to the fluctuation of the separation distance becomes large, making it difficult to mass-produce an image forming apparatus that satisfies stable image quality. . When the separation distance of the toner carrying member from the photosensitive member is larger than 1000 μm, the recoverability of the transfer residual toner to the developing device is lowered, and fogging due to poor recovery is likely to occur. Further, since the followability of the toner with respect to the latent image on the photosensitive member is lowered, there is a tendency that the image quality is lowered such as a lower resolution and a lower image density.
[0152]
In the present invention, 5 to 50 g / m on the toner carrier.²The toner layers are preferably laminated so as to form a toner layer. The toner amount on the toner carrier is 5 g / m.²If it is smaller than 1, a sufficient image density is difficult to obtain, and the toner layer becomes uneven due to excessive charging of the toner. The amount of toner on the toner carrier is 50 g / m.²If the amount is larger than that, toner scattering tends to occur.
[0153]
The surface roughness Ra (JIS centerline average roughness) of the toner carrier used in the present invention is preferably in the range of 0.2 to 3.5 μm. When Ra is less than 0.2 μm, the amount of charge on the toner carrier increases, and the developability tends to be insufficient. On the other hand, when Ra exceeds 3.5 μm, unevenness of toner stacking on the toner carrier is likely to occur, resulting in uneven density on the image. The surface roughness Ra is more preferably in the range of 0.5 to 3.0 μm.
[0154]
In the present invention, the surface roughness Ra of the toner carrier is measured using a surface roughness measuring device (Surfcoder SE-30H, manufactured by Kosaka Laboratory Co., Ltd.) based on JIS surface roughness “JIS B 0601”. This corresponds to the centerline average roughness. Specifically, a 2.5 mm portion as the measurement length a is extracted from the roughness curve in the direction of the center line, the center line of this extraction portion is the X axis, the direction of the vertical magnification is the Y axis, and the roughness curve is y When represented by = f (x), the value obtained by the following formula (3) is represented in micrometers (μm).
[0155]
[Equation 5]

As the toner carrier having a surface roughness (Ra) in the above range, a conductive cylinder formed of a metal or alloy such as aluminum or stainless steel is preferably used. A conductive cylinder may be formed of a resin composition having sufficient mechanical strength and conductivity, or a conductive rubber roller may be used. Further, the present invention is not limited to the cylindrical shape as described above, and may be an endless belt that is rotationally driven. Moreover, the resin layer may be used for these as a coating layer.
[0156]
In order to make the surface roughness (Ra) of the toner carrier in the present invention within the above range, for example, it is possible to change the polishing state of the surface layer of the toner carrier. That is, if the surface of the toner carrier is roughened, the surface roughness can be increased, and if the surface is finely polished, the surface roughness can be reduced.
Further, when a resin layer is used, the surface roughness can be adjusted also by adding conductive fine particles and the like, which will be described later, to the resin layer, and the particle size and addition amount.
[0157]
Furthermore, since the magnetic toner according to the present invention has a high charging ability, it is preferable to control the total charge amount of the toner during development.
The surface of the toner carrier according to the present invention is preferably coated with a resin layer in which conductive fine particles and / or a lubricant are dispersed.
[0158]
As the conductive fine particles contained in the resin layer covering the surface of the toner carrier, conductive metal oxides such as carbon black, graphite, and conductive zinc oxide, and metal double oxides are used alone or in combination of two or more. Is preferred. Examples of the resin in which the conductive fine particles and / or the lubricant are dispersed include phenol resins, epoxy resins, polyamide resins, polyester resins, polycarbonate resins, polyolefin resins, silicone resins, fluorine resins, styrene resins. Known resins such as resins and acrylic resins are used. A thermosetting resin or a photocurable resin is particularly preferable.
[0159]
In the non-contact developing method, it is preferable that the moving speed of the toner carrying member that carries the toner in the developing process and transports it to the developing unit is different from the moving speed of the photosensitive member. By providing such a speed difference, toner particles can be sufficiently supplied from the toner carrying member side to the photosensitive member side, and a good image can be obtained.
[0160]
In the present invention, the surface of the toner carrier that carries the toner may move in the same direction as the moving direction of the image carrier surface, or may move in the opposite direction. When the moving direction is the same direction, it is desirable that the ratio is 70% or more with respect to the moving speed of the image carrier. If it is less than 70%, the image quality may be poor. The higher the moving speed ratio, the more toner is supplied to the development site, the more frequently the toner is desorbed from the latent image, and the unnecessary parts are scraped off and applied to the necessary parts. Thus, an image faithful to the latent image can be obtained. Specifically, the moving speed of the toner carrier surface is preferably 0.7 to 7.0 times the moving speed of the image carrier surface.
[0161]
In the developing unit, an AC electric field is applied to transfer the magnetic toner to an electrostatic latent image for development, and the AC electric field at this time has at least a peak-to-peak electric field strength of 3 × 10.⁶~ 1 × 10⁷V / m and a frequency of 100 to 5000 Hz are preferable. It is also a preferred form that a DC bias is further superimposed.
[0162]
Next, the charging process will be described.
In the present invention, a non-contact charging step such as a charging step using a charging device using corona discharge may be used, but a contact charging method in which a charging member is brought into contact with the photosensitive member is a preferable charging method. In this case, it is preferable to use a charging roller as the contact charging member.
As a preferable process condition when using the charging roller as shown in FIG. 1, the contact pressure of the roller member is 4.9 to 490 N / m (5 to 500 g / cm), and the DC voltage or the AC voltage is superimposed on the DC voltage. Used. In the case of using a DC voltage superimposed with an AC voltage, AC voltage = 0.5 to 5 kVpp, AC frequency = 50 to 5 kHz, and DC voltage = ± 0.2 to ± 5 kV are preferable.
[0163]
Other charging means include a method using a charging blade and a method using a conductive brush. Even when these contact charging means are used, there is an effect that a high voltage becomes unnecessary and generation of ozone is reduced.
[0164]
The material of the charging roller and charging blade as the contact charging member is preferably conductive rubber, and a release coating may be provided on the surface thereof. As the releasable coating, nylon resin, PVdF (polyvinylidene fluoride), PVdC (polyvinylidene chloride), and fluorine acrylic resin are applicable.
[0165]
The roller member used as the contact charging member preferably has an Asker C hardness of 50 degrees or less. If the hardness is too low, the shape is not stable, so that the contact property with the member to be charged is deteriorated and stable chargeability cannot be obtained. On the other hand, if the hardness is too high, a charging contact portion cannot be secured between the charged body and the micro contact property to the charged body surface is deteriorated.
Furthermore, by providing a relative speed difference between the moving speed of the surface of the charging member forming the contact portion and the moving speed of the surface of the image carrier, higher contact is achieved at the contact portion between the contact charging member and the image carrier. You can get sex.
[0166]
The contact charging member and the image carrier are preferably moved in the opposite directions at the contact portion. For example, it is desirable that the contact charging member is driven to rotate, and the rotation direction of the contact charging member is rotated in the direction opposite to the moving direction of the image carrier surface at the contact portion.
[0167]
Although it is possible to move the charging member in the same direction as the moving direction of the surface of the image carrier, a difference in speed is possible, but the contact charging property depends on the ratio between the peripheral speed of the image carrier and the peripheral speed of the charging member. In order to obtain the same peripheral speed ratio as that in the reverse direction, the rotation speed of the charging member in the forward direction is larger than that in the reverse direction. Therefore, it is advantageous in terms of the rotation speed to move the charging member in the reverse direction. The peripheral speed ratio described here can be expressed by the following equation (4).
[0168]
[Formula 6]
Peripheral speed ratio (%) = (charging member peripheral speed / image carrier peripheral speed) x 100 (4)
The charging bias applied to the contact charging member can obtain good chargeability only with a DC voltage, but an AC voltage (alternating voltage) may be superimposed on the DC voltage as in the above-described apparatus shown in FIG.
[0169]
The alternating voltage at this time preferably has a peak voltage of less than 2 × Vth (Vth: discharge start voltage when a DC voltage is applied) (V).
[0170]
If the peak voltage of the AC voltage applied to the DC voltage is not less than 2 × Vth, the potential on the image carrier may become unstable. The AC voltage when applying a bias in which an AC voltage is superimposed on the DC voltage is more preferably a peak voltage less than Vth. As a result, the image carrier can be charged without a substantial discharge phenomenon.
Next, the transfer process will be described.
[0171]
In the present invention, a non-contact transfer step such as a transfer step using a transfer device using corona discharge may be used, but preferably the transfer member is in contact with the photoconductor via a transfer material. This is a contact transfer method in which transfer is performed by the above method.
[0172]
The contact pressure of the transfer member is preferably 2.9 N / m (3 g / cm) or more, more preferably 19.6 N / m (20 g / cm) or more. If the linear pressure as the contact pressure is less than 2.9 N / m (3 g / cm), it is not preferable because transfer of the transfer material and transfer failure are likely to occur.
[0173]
Further, as a transfer member in the contact transfer process, an apparatus having a transfer roller or a transfer belt is used. As an example of the transfer roller, it is composed of at least a core metal and a conductive elastic layer, and the conductive elastic layer has a volume resistance of 10 such as urethane or EPDM in which a conductive material such as carbon is dispersed.⁶~Ten^TenThe transfer bias is applied by a transfer bias power source.
[0174]
Next, the photoreceptor used in the present invention will be described below.
[0175]
As a photoreceptor, a-Se, CdS, ZnO₂A photosensitive drum or a photosensitive belt having a photoconductive insulating material layer such as OPC (organic photoreceptor) or a-Si is preferably used. In particular, in the present invention, it is preferable to use a photoreceptor whose surface is composed mainly of a polymer binder. For example, when a protective film (protective layer) mainly composed of a resin is provided on an inorganic photoreceptor such as selenium or amorphous silicon, or a surface comprising a charge transport material and a resin as a charge transport layer of a function-separated organic photoreceptor When a layer is provided, a protective layer mainly composed of resin may be provided on the surface layer. These surface layers (or protective layers) preferably have releasability, and as means for actually imparting releasability,
(1) Use a resin having a low surface energy as the resin itself constituting the film.
(2) Add additives that impart water repellency and lipophilicity.
(3) Means such as dispersing a material having high releasability in the form of a powder. Examples of (1) include introducing functional groups such as fluorine-containing groups and silicone-containing groups into the structure of the structural unit of the resin. Examples of the additive (2) that imparts water repellency and lipophilicity include surfactants. Examples of the material having high releasability (3) include compounds containing fluorine atoms, that is, polytetrafluoroethylene, polyvinylidene fluoride, and carbon fluoride.
[0176]
By these means, the contact angle of water on the surface of the photoreceptor can be 85 degrees or more, and the transferability of toner and the durability of the photoreceptor can be further improved. The contact angle of the photoreceptor surface with water is preferably 90 degrees or more. In the present invention, among the above means (1) to (3), it is preferable to disperse in the outermost surface layer of a releasable powder such as fluorine-containing resin as in (3). As the conductive powder, it is particularly preferable to use polytetrafluoroethylene.
[0177]
In order to contain these releasable powders on the surface, a layer in which the releasable powders are dispersed in a binder resin is provided on the outermost surface of the photoconductor, or the photoconductor itself is mainly composed of resin. In the case of an organic photoconductor, a releasable powder may be dispersed in the uppermost layer without newly providing a surface layer. The addition amount of the releasable powder is preferably 1 to 60% by mass and more preferably 2 to 50% by mass with respect to the total amount of the surface layer. If the amount of the release powder added is less than 1% by mass, the effect of improving the transferability of the toner and the durability of the photoreceptor is insufficient, and if it exceeds 60% by mass, the strength of the protective film is reduced, This is not preferable because the amount of light incident on the body is significantly reduced.
[0178]
The contact angle is measured using a drop-type contact angle meter (for example, contact angle meter CA-X type manufactured by Kyowa Interface Science Co., Ltd.) where the free surface of water is in contact with the photoconductor. It is defined by the angle formed by the surface (the angle inside the liquid).
[0179]
In addition, the said measurement shall be performed at room temperature (about 21-25 degreeC).
In the present invention, the contact charging method in which the charging unit abuts the charging member on the photosensitive member is a preferable charging method, and the load on the surface of the photosensitive member is different from the method using corona discharge in which the charging unit does not contact the photosensitive member. Therefore, providing a protective layer (protective film) on the surface of the photoreceptor has a remarkable effect of improving durability, and is one of the preferred application forms.
[0180]
In the present invention, since it is preferable to apply a contact charging method or a contact transfer method, a photoreceptor having a small diameter of 50 mm or less is particularly effectively used. That is, when the diameter of the photoconductor used in image formation is small, the curvature with respect to the same linear pressure is large, and pressure concentration tends to occur at the contact portion. Although it is considered that the same phenomenon occurs in the belt photoreceptor, the present invention is also effective for an image forming apparatus having a radius of curvature of 25 mm or less at the transfer portion.
[0181]
One preferred embodiment of the photoreceptor used in the present invention will be described below. Specifically, a laminated photosensitive layer having a structure in which a charge generation layer and then a charge transport layer are laminated in this order on a conductive substrate is one preferred example.
[0182]
Examples of conductive substrates include metals such as aluminum and stainless steel, aluminum alloys, plastics having a coating layer of indium oxide-tin oxide alloy, paper impregnated with conductive particles, plastics, and plastics having conductive polymers. Cylinders and films are used.
On these conductive substrates, the adhesion of the photosensitive layer is improved, the coating property is improved, the substrate is protected, the defects on the substrate are coated, the charge injection from the substrate is improved, and the photosensitive layer is protected from electrical breakdown. For the purpose, an undercoat layer may be provided.
[0183]
Undercoat layer is polyvinyl alcohol, poly-N-vinylimidazole, polyethylene oxide, ethyl cellulose, methyl cellulose, nitrocellulose, ethylene-acrylic acid copolymer, polyvinyl butyral, phenol resin, casein, polyamide, copolymer nylon, glue, gelatin, polyurethane It is made of a material such as aluminum oxide. The thickness of the undercoat layer is usually 0.1 to 10 μm, preferably about 0.1 to 3 μm.
[0184]
The charge generation layer is composed of azo pigments, phthalocyanine pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, squarylium dyes, pyrylium salts, thiopyrylium salts, triphenylmethane dyes, selenium, amorphous silicon, etc. A charge generating material such as an inorganic material is dispersed in a suitable binder resin and coated, or is formed by vapor deposition. Examples of the binder resin include polycarbonate resin, polyester resin, polyvinyl butyral resin, polystyrene resin, acrylic resin, methacrylic resin, phenol resin, silicon resin, epoxy resin, and vinyl acetate resin. A binder resin can be arbitrarily selected. The amount of the binder resin contained in the charge generation layer is preferably 80% by mass or less, and more preferably 0 to 60% by mass with respect to the entire charge generation layer. The film thickness of the charge generation layer is preferably 5 μm or less, particularly preferably 0.05 to 2 μm.
[0185]
The charge transport layer has a function of receiving charge carriers from the charge generation layer in the presence of an electric field and transporting them. The charge transport layer is formed by dissolving a charge transport material in a solvent together with a binder resin, if necessary, and coating. The thickness of the charge generation layer is generally 5 to 40 μm. Examples of charge transport materials include polycyclic aromatic compounds having a structure such as biphenylene, anthracene, pyrene, and phenanthrene in the main chain or side chain, nitrogen-containing cyclic compounds such as indole, carbazole, oxadiazole, and pyrazoline, hydrazone compounds, Examples include styryl compounds, selenium, selenium-tellurium, amorphous silicon, and cadmium sulfide.
[0186]
In addition, as a binder resin for dispersing these charge transport materials, polycarbonate resin, polyester resin, polymethacrylic acid ester, polystyrene resin, acrylic resin, polyamide resin, and other organic materials such as poly-N-vinylcarbazole and polyvinyl anthracene are used. A photoconductive polymer is mentioned.
[0187]
Furthermore, you may provide a protective layer separately as a surface layer. As the resin for the protective layer, polyester, polycarbonate, acrylic resin, epoxy resin, phenol resin, or curing agents for these resins can be used alone or in combination of two or more.
[0188]
Moreover, you may disperse | distribute electroconductive fine particles in resin of a protective layer. Examples of the conductive fine particles include metals and metal oxides, and preferably zinc oxide, titanium oxide, tin oxide, antimony oxide, indium oxide, bismuth oxide, tin oxide-coated titanium oxide, tin-coated indium oxide, and antimony. Examples thereof include ultrafine particles of coated tin oxide and zirconium oxide. These conductive fine particles may be used alone or in combination of two or more. In general, when particles are dispersed in a protective layer, it is necessary that the particle diameter of the fine particles is smaller than the wavelength of the incident light in order to prevent scattering of incident light by the dispersed fine particles, and the particles are dispersed in the protective layer in the present invention. The particle diameter of the conductive fine particles is preferably 0.3 μm or less. Further, the content of the conductive fine particles in the protective layer is preferably 2 to 90% by mass, and more preferably 5 to 80% by mass with respect to the total weight of the protective layer. The thickness of the protective layer is preferably from 0.1 to 10 μm, more preferably from 1 to 7 μm.
The surface layer can be applied by spray coating, beam coating or penetration (dipping) coating of the resin dispersion.
[0189]
In the present invention, it is preferable that an electrostatic latent image forming step for forming an electrostatic latent image on the charging surface of the image carrier is performed by an image exposure unit. The image exposure means for forming the electrostatic latent image is not limited to the laser scanning exposure means for forming a digital latent image, and other light emitting elements such as normal analog image exposure and LEDs may be used. It does not matter as long as it can form an electrostatic latent image corresponding to image information, such as a combination of a light emitting element such as a fluorescent lamp and a liquid crystal shutter.
<3> Process cartridge of the present invention
The present invention also relates to a book for forming an image by transferring a toner to a latent electrostatic image formed on an image carrier to be visualized to form a toner image, and transferring the toner image to a transfer material. A process cartridge configured to be detachable from an image forming apparatus in which the image forming method of the invention is used. At least two selected from a photosensitive member, a charging unit, and a developing unit are integrally supported, and toner is The process cartridge is a magnetic toner of the present invention.
<4> Method for measuring physical properties used in the present invention
The method for measuring various physical property data in the present invention is described in detail below.
(1) Ratio of iron element content (B) to carbon element content (A) present on the toner surface (B / A)
The ratio (B / A) of the iron element content (B) to the carbon element content (A) present on the toner surface in the present invention is calculated by performing surface composition analysis by ESCA (X-ray photoelectron spectroscopy). .
[0190]
In the present invention, the ESCA apparatus and measurement conditions are as follows.
Equipment used: PHI (Physical Electronics Industries, Inc.)
1600S X-ray photoelectron spectrometer
Measurement conditions: X-ray source MgKα (400W)
Spectral region 800μmφ
In the present invention, the surface atomic concentration (atomic%) is calculated from the measured peak intensity of each element using a relative sensitivity factor provided by PHI.
[0191]
As the measurement sample, toner is used. When an external additive is added to the toner, the toner is washed with a solvent that does not dissolve the toner, such as isopropanol, and the measurement is performed after removing the external additive. Do.
(2) Average circularity of toner
The circularity in the present invention is used as a simple method for quantitatively expressing the shape of the toner particles. In the present invention, the toner particle shape is measured using a flow type particle image analyzer FPIA-1000 manufactured by Toa Medical Electronics. The circularity is obtained by the following formula (2). Furthermore, as shown by the following formula (5), a value obtained by dividing the total circularity of all the measured particles by the total number of particles is defined as an average circularity.
[0192]
[Expression 7]

[0193]
[Equation 8]

Note that “FPIA-1000”, which is a measuring apparatus used in the present invention, calculates the circularity of each toner particle, and then calculates the average circularity. Divide 1.000 into 0.010 intervals, 0.400 or more, less than 0.410, 0.410 or more, but less than 0.420 ... 0.990 or more, but less than 1.000 or 1.000, and calculate the average circularity using the center value and frequency of the dividing points. The calculation method is used.
[0194]
There is very little error between each value of the average circularity calculated by this calculation method and each value of the average circularity calculated by the calculation formula that directly uses the circularity of each particle described above. Since it is negligible, the present invention uses the concept of the calculation formula that directly uses the circularity of each particle described above for reasons of handling data such as shortening the calculation time and simplifying the calculation calculation formula. However, such a calculation method which is partially changed is used.
[0195]
The circularity in the present invention is an index indicating the degree of unevenness of toner particles, and is 1.000 when the toner particles are completely spherical, and the circularity becomes smaller as the surface shape becomes more complicated.
[0196]
As a specific method for measuring the circularity, about 5 mg of toner is dispersed in 10 ml of water in which about 0.1 mg of a nonionic surfactant is dissolved, and the dispersion is prepared, and ultrasonic waves (20 kHz, 50 W) are used as the dispersion. Irradiation is performed for 5 minutes, the dispersion concentration is set to 5000 to 20000 particles / μl, and the circularity distribution of particles having a circle-equivalent diameter of 3 μm or more is measured using the flow type particle image measuring apparatus.
[0197]
The outline of the measurement is described in the catalog (June 1995 edition) of FPIA-1000 issued by Toa Medical Electronics Co., Ltd., the operation manual of the measuring apparatus, and Japanese Patent Application Laid-Open No. 8-136439. It is.
[0198]
The sample dispersion is passed through a flow path (spread along the flow direction) of a flat and flat transparent flow cell (thickness: about 200 μm). The strobe and the CCD camera are mounted on the flow cell so as to be opposite to each other so as to form an optical path that passes through the thickness of the flow cell. While the sample dispersion is flowing, strobe light is irradiated at 1/30 second intervals to obtain an image of the toner particles flowing through the flow cell, so that each toner particle has a certain range parallel to the flow cell. Photographed as a two-dimensional image. From the area of the two-dimensional image of each particle, the diameter of a circle having the same area is calculated as the equivalent circle diameter. The circularity of each particle is calculated from the projected area of the two-dimensional image of each toner particle and the perimeter of the projected image using the above circularity calculation formula.
(3) Toner particle size distribution
As a measuring device, a Coulter counter TA-II type (manufactured by Coulter) was connected to an interface (manufactured by Nikkaki) that outputs number distribution and volume distribution, and a CX-1 personal computer (manufactured by Canon). Prepare 1% NaCl aqueous solution using grade sodium chloride. For example, ISOTON R-II (manufactured by Coulter Scientific Japan) can be used. As a measuring method, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersing agent to 100 to 150 ml of the electrolytic aqueous solution, and 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the volume and number of toners are measured using the Coulter counter TA-II type with a 100 μm aperture as the aperture. Calculate the volume distribution and number distribution of particles of ˜40 μm. Then, the weight-based weight average diameter D4 obtained from the number-average particle diameter (D1) volume distribution (the median value of each channel is the representative value for each channel) and the weight-based weight distribution of 12.7 μm or more obtained from the volume distribution Ask for.
[0199]
【Example】
Hereinafter, the present invention will be specifically described with reference to production examples and examples, but this does not limit the present invention in any way. The number of parts or% described in an Example shows a mass part or mass%.
<1> Manufacture of iron oxide as a magnetic material
(Manufacture of surface-treated iron oxide 1)
An aqueous solution containing ferrous hydroxide was prepared by mixing 1.0 to 1.1 equivalents of a caustic soda solution with respect to iron ions in an aqueous ferrous sulfate solution.
[0200]
While maintaining the pH of the aqueous solution at around 9, air was blown in and an oxidation reaction was performed at 70 ° C. or higher to prepare a slurry liquid for generating seed crystals. Next, after adding ferrous sulfate aqueous solution to this slurry liquid so as to be 0.9 to 1.2 equivalents relative to the initial alkali amount (sodium component of caustic soda), the slurry liquid is maintained at pH 8 and oxidized while blowing air. The reaction was promoted, and the magnetic iron oxide particles produced after the oxidation reaction were washed, filtered and once taken out. At this time, a small amount of water-containing sample was collected and the water content was measured.
[0201]
Next, this water-containing sample was re-dispersed in another aqueous medium without drying, and then the pH of the re-dispersed liquid was adjusted to about 6, and the silane coupling agent (n-C_TenH_{twenty one}Si (OCH_Three )_Three) Was added to 100 parts of magnetic iron oxide (the amount of magnetic iron oxide was calculated by subtracting the water content from the water-containing sample) and subjected to a coupling treatment. The produced hydrophobic iron oxide particles were washed, filtered and dried by a conventional method, and then the slightly agglomerated particles were pulverized to obtain surface-treated iron oxide 1. The volume average particle diameter of the surface-treated iron oxide 1 was 0.18 μm.It was.
(tableProduction of surface-treated iron oxide 3)
In the production of the surface-treated iron oxide 1, the surface-treated iron oxide 3 was obtained in the same manner except that the amount of the silane coupling agent added was 0.7 parts.
(Manufacture of surface-treated iron oxide 4)
In the production of the surface-treated iron oxide 1, the surface-treated iron oxide 4 was obtained in the same manner except that the amount of the silane coupling agent added was 0.3 parts.
(Manufacture of surface-treated iron oxide 5)
  In a flask equipped with a stirrer, an inert gas introduction tube, a reflux condenser, and a thermometer, 200 parts of deionized water in which 0.1 part of polyvinyl alcohol (PVA-205, manufactured by Kuraray Co., Ltd.) was dissolved was charged. A mixture prepared by dissolving 87.5 parts of benzoyl peroxide in a previously prepared polymerizable monomer composed of 97.5 parts of styrene and 2.5 parts of glycidyl methacrylate was stirred at a high speed to obtain a uniform suspension. Next, the mixture was heated to 80 ° C. while blowing nitrogen gas, and stirred at this temperature for 5 hours to carry out a polymerization reaction. Thereafter, filtration, washing with water and drying were performed to obtain a resin containing an epoxy group.
[0202]
On the other hand, the oxidation reaction proceeds in the same manner as in the production of the surface-treated iron oxide 1, the magnetic iron oxide particles generated after the oxidation reaction are washed, filtered, dried without surface treatment, and the aggregated particles are crushed. Treatment gave untreated iron oxide particles. 80 parts of the untreated iron oxide particles and 20 parts of the epoxy group-containing resin are kneaded for 30 minutes under the conditions of 180 ° C. and 100 rpm using a lab plast mill, and the epoxy group-containing resin and untreated oxidation are mixed. Reacted with iron particles. After cooling, it was pulverized to obtain surface-treated iron oxide 5.
<2> Manufacture of magnetic toner
(Manufacture of magnetic toner A)
1.0M-Na in 292 parts of ion-exchanged water_ThreePO_FourAfter adding 46 parts of an aqueous solution and heating to 70 ° C., 1.0M-CaCl₂Gradually add 67 parts of aqueous solution and add Ca_Three(PO_Four)₂An aqueous medium containing was obtained.
[0203]
Next, 83 parts of styrene, 17 parts of n-butyl acrylate, 0.6 part of divinylbenzene (purity 55%), saturated polyester resin (condensate with terephthalic acid / bisphenol A-EO, PO adduct, Mp11000, Tg 69 ° C., acid Attritor (Mitsui Miike Chemical Co., Ltd.) 5 parts, 12 parts negative charge control agent (monoazo dye-based Fe compound), 2 parts α-methylstyrene dimer, 1 part surface-treated iron oxide ) Was uniformly dispersed and mixed to obtain a monomer composition.
[0204]
This monomer composition was heated to 70 ° C., and 12 parts of an ester wax having an endothermic peak temperature in the DSC curve of 80 ° C. was added and mixed therewith, and 5 parts of benzoyl peroxide was added thereto as a polymerization initiator.
[0205]
The monomer composition is charged into the aqueous medium, 70 ° C., N₂Under an atmosphere, the mixture was stirred and granulated at 10,000 rpm for 10 minutes with a TK homomixer (Special Machine Industries Co., Ltd.). Thereafter, the mixture was reacted at 70 ° C. for 24 hours while stirring with a paddle stirring blade. Thereafter, the suspension was cooled, and then diluted hydrochloric acid was added to dissolve calcium phosphate as a dispersion stabilizer. After repeating filtration and washing with water, toner particles were obtained. The THF insoluble content of the toner particles was measured and found to be 20% based on the binder resin component.
[0206]
100 parts of the toner particles and 1.5 parts of a hydrophobic silica fine powder having a number average primary particle size of 10 nm, the surface of which was treated with hexamethyldisilazane and then treated with silicone oil, were mixed with a Henschel mixer (Mitsui Miike Chemical Co., Ltd.). Magnetic toner A was prepared by mixing. Table 2 shows the physical properties of the magnetic toner A. In addition, it shows in Table 1 about the used raw material.
[0207]
[Table 1]

[0208]
[Table 2]

(MagneticProduction of toner C)
  Magnetic toner C was prepared in the same manner as magnetic toner A except that surface-treated iron oxide 3 was used instead of surface-treated iron oxide 1. Table 2 shows the physical properties of the magnetic toner C.
(Manufacture of magnetic toner D)
  Similar to the production of magnetic toner A except that 2.3 parts of unsaturated polyester resin (condensate with fumaric acid / bisphenol A-PO adduct, Mp10000, Tg 65 ° C., acid value 12 mg KOH / g) was used instead of divinylbenzene. Thus, magnetic toner D was prepared. Table 2 shows the physical properties of the magnetic toner D. This toner particle was measured for THF-insoluble content, which was 35% based on the binder resin component.
(Manufacture of magnetic toner E)
  Magnetic toner E was prepared in the same manner as magnetic toner A except that 2 parts of t-dodecyl mercaptan was added in place of α-methylstyrene dimer. Table 2 shows the physical properties of the magnetic toner E. The toner particles were measured for THF-insoluble content, which was 20% based on the binder resin component.
(Manufacture of magnetic toner F)
  Magnetic toner F was prepared in the same manner as magnetic toner A except that t-butylperoxy-2-ethylhexanoate was used instead of benzoyl peroxide. Table 2 shows the physical properties of the magnetic toner F. This toner particle was measured for THF-insoluble content, which was 30% based on the binder resin component.
(Manufacture of magnetic toner G)
  Magnetic toner G was prepared by mixing 100 parts of toner particles produced in the production of magnetic toner A and 1.5 parts of hydrophobic silica fine powder having a number average primary particle size of 10 nm treated with hexamethyldisilazane using a Henschel mixer. Table 2 shows the physical properties of the magnetic toner G.
(Manufacture of magnetic toner H)
Magnetic toner H was obtained in the same manner as in the production of magnetic toner A, except that the amount of ester wax used was 51 parts. Table 2 shows the physical properties of the magnetic toner H.
(Manufacture of magnetic toner I)
  Magnetic toner I was obtained in the same manner as in the production of magnetic toner A, except that the amount of ester wax used was 0.4 parts. Table 2 shows the physical properties of the magnetic toner I.
(Manufacture of magnetic toner J)
  Magnetic toner J was obtained in the same manner as magnetic toner A except that 12 parts of low molecular weight polyethylene wax having an endothermic peak temperature of 112 ° C. in DSC was used instead of ester wax. Table 2 shows the physical properties of the magnetic toner J.
(Manufacture of magnetic toner K)
  A comparative magnetic toner K was obtained in the same manner as in the production of the magnetic toner A except that the surface-treated iron oxide 4 was used instead of the surface-treated iron oxide 1. Table 2 shows the physical properties of the comparative magnetic toner K.
(Manufacture of magnetic toner L)
  A comparative magnetic toner L was obtained in the same manner as in the production of the magnetic toner A except that 120 parts of the surface-treated iron oxide 5 was used instead of the surface-treated iron oxide 1. Table 2 shows the physical properties of the comparative magnetic toner L.
[0209]
(Manufacture of magnetic toner M)
1.0M-Na in 730 parts of ion-exchanged water_ThreePO_FourAfter adding 46 parts of an aqueous solution and heating to 60 ° C., 1.0M-CaCl₂Gradually add 67 parts of aqueous solution and add Ca_Three(PO_Four)₂An aqueous medium containing was obtained.
[0210]
Next, 80 parts of styrene, 20 parts of n-butyl acrylate, 0.6 parts of divinylbenzene, 1 part of negative charge control agent (monoazo dye-based Fe compound) and 5 parts of surface-treated iron oxide 5120 parts using an attritor Mixed and dispersed.
[0211]
Next, this dispersion was heated to 60 ° C., and 12 parts of ester wax having an endothermic peak temperature in DSC of 80 ° C. was added and mixed therewith, and 2,2′-azobis (2,4- Dimethylvaleronitrile) (V65) 3 parts and 2,2′-azobisisobutyronitrile (AIBN) 4 parts were added to obtain a monomer composition.
[0212]
The monomer composition is charged into the aqueous medium, and 60 ° C., N₂In an atmosphere, the mixture was stirred for 10 minutes at 10,000 rpm with a TK homomixer and granulated. Thereafter, the mixture was reacted at 60 ° C. for 10 hours while stirring with a paddle stirring blade.
[0213]
After completion of the reaction, the suspension was cooled, diluted hydrochloric acid was added to adjust the pH to 1.0, and the mixture was stirred for 1 hour. Thereafter, the mixture was filtered and dried to obtain a toner having a weight average particle diameter of 7.0 μm.
[0214]
A comparative magnetic toner M was prepared by mixing 100 parts of the toner particles and 1.5 parts of the hydrophobic silica fine powder used in the production of the magnetic toner A with a Henschel mixer. Table 2 shows the physical properties of the comparative magnetic toner M. This toner particle was measured for the THF-insoluble content, which was 65% based on the binder resin component.
(Manufacture of magnetic toner N)
369.5 g of PO adduct of bisphenol A, 146.4 g of EO adduct of bisphenol A, 126.0 g of terephthalic acid, 40.2 g of dodecenyl succinic acid and 77.7 g of trimellitic anhydride are placed in a glass four-necked flask, thermometer, stainless steel A stir bar, a condenser, and a nitrogen introduction tube were attached, and the reaction was carried out at 220 ° C. under a nitrogen stream in a mantle heater. The degree of polymerization was monitored from the softening point according to ASTM E28-67, and the reaction was terminated when the softening point reached 110 ° C.
Next, 65 parts of styrene, 35 parts of 2-ethylhexyl acrylate, 0.8 part of divinylbenzene, 5120 parts of surface-treated iron oxide, 10 parts of the polyester resin synthesized above, 2,2,2′-azobisisobutyronitrile 3.5 parts were added, put into an attritor, and dispersed at 10 ° C. for 5 hours to obtain a polymerizable monomer composition.
Next, 212.3 parts of the polymerizable monomer composition was added to 650 parts of an aqueous colloidal solution of tricalcium phosphate 4% prepared in advance in a 2 liter glass separable flask, and TK homomixer was used. Granulation was performed at room temperature for 2 minutes at a rotation speed of 10,000 rpm.
[0215]
Next, a four-necked glass lid was put on, a reflux condenser, a thermometer, a nitrogen introduction tube, and a stainless steel stirring rod were attached and installed in an electric heating mantle heater. While stirring under nitrogen, the temperature was raised to 85 ° C. as the first stage polymerization, and the reaction was carried out for 10 hours to obtain seed particles. This was cooled to room temperature to obtain precursor particles. Next, 13 parts of styrene prepared by an ultrasonic oscillator in an aqueous suspension of the precursor particles, 7 parts of 2-ethylhexyl acrylate, 0.4 part of 2,2′-azobisisobutyronitrile (AIBN), 40.7 parts of an aqueous emulsion composed of 0.22 parts of divinylbenzene, 0.1 part of sodium lauryl sulfate, and 20 parts of water was added dropwise to swell the precursor particles.
[0216]
Then, while continuing stirring under nitrogen, the temperature was raised to 85 ° C. as the second-stage polymerization and reacted for 10 hours. After cooling, dissolve the dispersion medium with 10% aqueous hydrochloric acid, filter, wash with water, air dry, 45 ° C for 12 hours, dry under reduced pressure at 20mmHg, classify with an air classifier, and toner with a weight average particle size of 7.8μm Particles were obtained. The toner particles were measured for THF-insoluble content and found to be 35% based on the binder resin component.
[0217]
100 parts of the toner particles and 1.5 parts of hydrophobic silica fine powder used in the production of the magnetic toner A were mixed with a Henschel mixer to prepare a magnetic toner N. Table 2 shows the physical properties of the magnetic toner N.
(Manufacture of magnetic toner O)
The toner particles L obtained in the production of the magnetic toner L were melt-kneaded with a biaxial extruder heated to 160 ° C. Thereafter, the cooled kneaded product was coarsely pulverized with a hammer mill, and the coarsely pulverized product was finely pulverized with a jet mill. Further, the obtained pulverized product was classified. When the THF-insoluble matter was measured for this classified powder, it was 0% based on the binder resin component.
[0218]
100 parts of this classified powder and 1.5 parts of hydrophobic silica fine powder used in the production of magnetic toner A were mixed with a Henschel mixer to prepare magnetic toner O. Table 2 shows the physical properties of the magnetic toner O.
(Manufacture of magnetic toner P)
The classified powder obtained in the production of the magnetic toner O was surface-modified (spheroidized) by mechanical impact force to obtain toner particles. A magnetic toner P was prepared by mixing 100 parts of the toner particles and 1.5 parts of hydrophobic silica fine powder used in the production of the magnetic toner A with a Henschel mixer. Table 2 shows the physical properties of the magnetic toner P.
(Manufacture of magnetic toner Q)
200 parts of xylene was placed in the reaction vessel and the temperature was raised to the reflux temperature. To this was added dropwise a mixed solution of 83 parts of styrene, 17 parts of n-butyl acrylate and 2.0 parts of di-tert-butyl peroxide, and the solution polymerization was completed in 7 hours under reflux of xylene. A low molecular weight resin was obtained.
[0219]
On the other hand, 83 parts of styrene, 17 parts of n-butyl acrylate, 0.5 part of divinylbenzene, 0.2 part of polyvinyl alcohol, 200 parts of water, and 0.3 part of benzoyl peroxide were mixed and suspended in another reaction vessel. The suspension dispersion was heated and maintained at 80 ° C. for 24 hours under a nitrogen atmosphere. After cooling, the filtrate was filtered, washed with water, and dried to obtain high molecular weight resin particles. The THF insoluble content of the resin particles was measured and found to be 73%.
[0220]
Next, 40 parts of high molecular weight resin particles, 60 parts of low molecular weight resin, 2 parts of negative charge control agent (monoazo dye-based Fe compound), 5120 parts of surface-treated iron oxide, 12 parts of ester wax having a maximum endothermic peak of 80 ° C Were mixed with a blender, melt kneaded with a biaxial extruder heated to 160 ° C., the cooled kneaded product was coarsely pulverized with a hammer mill, and the coarsely pulverized product was finely pulverized with a jet mill.
Subsequently, the obtained particles were subjected to surface modification (spheronization) treatment, and then classified. When the THF-insoluble matter was measured for this classified powder, it was 2% based on the binder resin component.
[0221]
Further, 100 parts of the classified powder and 1.5 parts of the hydrophobic silica fine powder used in the production of the magnetic toner A were mixed with a Henschel mixer to prepare a magnetic toner Q. Table 2 shows the physical properties of the magnetic toner Q.
(Manufacture of magnetic toner R)
In a reaction vessel, 1.2 parts of ethylene glycol dimethacrylate, 1.1 parts of n-dodecyl mercaptan, 83 parts of styrene, 17 parts of n-butyl acrylate, 2.4 parts of azobisisobutyronitrile, 0.2 part of polyvinyl alcohol, and 200 parts of water are mixed. The suspension was dispersed. The suspension dispersion was heated and held at 90 ° C. for 10 hours under a nitrogen atmosphere. After cooling, the filtrate was filtered, washed with water, and dried to obtain high molecular weight resin particles. The THF insoluble content of the resin particles was measured and found to be 25%.
[0222]
Next, 100 parts of high molecular weight resin particles, 2 parts of negative charge control agent (monoazo dye-based Fe compound), 5120 parts of surface-treated iron oxide, and 12 parts of ester wax having a maximum endothermic peak of 80 ° C. were mixed in a blender. This was melt kneaded with a biaxial extruder heated to 160 ° C., the cooled kneaded product was coarsely pulverized with a hammer mill, and then the coarsely pulverized product was finely pulverized with a jet mill.
Subsequently, the obtained particles were subjected to surface modification (spheronization) treatment, and then classified. The THF-insoluble matter in this classified powder was measured and found to be 1% based on the binder resin component.
Further, 100 parts by weight of the classified powder and 1.5 parts of the hydrophobic silica fine powder used in the production of the magnetic toner A were dry-mixed with a Henschel mixer to prepare a magnetic toner R. Table 2 shows the physical properties of the magnetic toner R.
<3> Manufacture of photoconductor
(Manufacture of photoconductor 1)
As the photoreceptor, an Al cylinder having a diameter of 30 mm was used as the conductive substrate. A layer having the structure as shown below was sequentially laminated thereon by dip coating to prepare a photoreceptor.
(1) Conductive coating layer: Mainly composed of tin oxide and titanium oxide powder dispersed in a phenolic resin. Film thickness 15μm.
(2) Undercoat layer: Mainly composed of modified nylon and copolymer nylon. Film thickness 0.6μm.
(3) Charge generation layer: Mainly composed of an azo pigment having absorption in a long wavelength region dispersed in polyvinyl butyral resin. Film thickness 0.6μm.
(4) Charge transport layer: Mainly composed of a hole-transporting triphenylamine compound dissolved in polycarbonate resin (molecular weight 20,000 by Ostwald viscosity method) at a mass ratio of 8:10, and polytetrafluoroethylene powder ( 10% by mass of a particle size of 0.2 μm) was added to the total solid content and dispersed uniformly. Film thickness 25μm. The contact angle with water was 95 degrees.
In addition, the measurement of the contact angle used pure water, and the apparatus used Kyowa Interface Science Co., Ltd. and the contact angle meter CA-X type.
[0223]
Examples 1 to 10 and Comparative Examples 1 to 8
As the image forming apparatus, LBP-1760 was remodeled and the one shown in FIG. 1 similar to the above-described embodiment was used.
An organic photoreceptor (OPC) drum was used as the electrostatic charge image carrier. A rubber roller charger in which conductive carbon is dispersed as a primary charging member and coated with nylon resin is brought into contact with this photoreceptor (contact pressure 60 g / cm), and a voltage obtained by superimposing an AC voltage 2.0 kVpp on a DC voltage −700 Vdc. To uniformly charge the surface of the photoconductor. Subsequent to primary charging, an electrostatic latent image is formed by exposing the image portion with laser light. At this time, the dark portion potential Vd = −700 V and the light portion potential VL = −150 V.
[0224]
The gap between the photosensitive drum and the developing sleeve is 290 μm, and the aluminum cylinder with a diameter of 16 mm is blasted on the surface of a resin layer having a layer thickness of about 7 μm and a JIS centerline average roughness (Ra) of 1.0 μm as a toner carrier. Using the developing sleeve formed above, a development magnetic pole of 90mT (900 gauss), a toner layer thickness regulating member of 1.0mm thickness and 1.0mm free length silicone rubber blade with a linear pressure of 29.4N / m (30g / cm) It was made to contact with.
・ Phenolic resin 100 parts
・ 90 parts of graphite (particle size approx. 7μm)
・ 10 parts of carbon black
Next, the DC bias component Vdc = −500 V, the superimposed AC bias component Vp-p = 1600 V, and f = 2000 Hz were used as the developing bias. The peripheral speed of the developing sleeve was 110% peripheral speed ratio (99 mm / sec) in the forward direction with respect to the peripheral speed of the photoreceptor (90 mm / sec).
In addition, as a transfer member, a transfer roller (made of ethylene-propylene rubber in which conductive carbon is dispersed, the volume resistance value of the conductive elastic layer is 10⁸Ωcm, surface rubber hardness 24 °, diameter 20 mm, contact pressure 59 N / m (60 g / cm)) at a constant speed relative to the peripheral speed of the photoconductor (90 mm / sec), and the transfer bias was 1.5 kV DC. .
As a fixing method, there was used a fixing device of LBP-1760 which does not have an oil application function and which is fixed by heating and pressing with a heater through a film. At this time, a pressure roller having a fluororesin surface layer was used, and the diameter of the roller was 30 mm. The fixing temperature was set to 180 ° C. and the nip width was set to 6 mm.
Using magnetic toners A to R as toners, an image was printed on 100 sheets under normal temperature, normal humidity (25 ° C., 60% RH) and low temperature, low humidity (10 ° C., 15% RH) environments. . As a transfer material, 75g / m²Paper was used.
The magnetic toners A to R were evaluated as follows.
[Evaluation of printout image]
1) Image density
With respect to the 50th printout image at room temperature and normal humidity, the relative density with respect to the printout image of the white background portion having a document density of 0.00 was measured by a Macbeth reflection densitometer RD918 (manufactured by Macbeth Co.).
A: Very good (above 1.40)
B: Good (1.35 or more, less than 1.40)
C: Normal (1.00 or more, less than 1.35)
D: Bad (less than 1.00)
2) fog
For the 100th printout image under low temperature and low humidity, the fog density (%) was calculated from the difference between the whiteness of the white background and the whiteness of the transfer paper, and the image fogging was evaluated. The fog density was measured with a “reflectometer” (manufactured by Tokyo Denshoku).
A: Very good (less than 1.5%)
B: Good (1.5% or more, less than 2.5%)
C: Normal (2.5% or more, less than 4.0%)
D: Poor (4.0% or more)
3) Transferability
The transfer residual toner on the photoconductor when a solid black image is formed is removed by taping with Mylar tape, and the Macbeth density of only Mylar tape on the paper is subtracted from the Macbeth density of the Mylar tape only on the paper. The numerical value was evaluated.
A: Very good (less than 0.05)
B: Good (0.05 to less than 0.1)
C: Normal (0.1 to less than 0.2)
D: Bad (over 0.2)
4) Fixability
50g / cm for the second printout image under low temperature and low humidity²The fixed image was rubbed with a soft thin paper and evaluated by the rate of decrease in image density (%) before and after rubbing.
A: Less than 5%
B: 5% or more, less than 10%
C: 10% or more, less than 20%
D: 20% or more
[Matching evaluation with image forming device]
1) Matching with photoconductor
After completion of the printout test, the occurrence of scratches on the surface of the photosensitive drum and the sticking of residual toner and the influence on the printout image were visually evaluated.
A: Not generated
B: Slight scratching is observed
C: There are sticking and scratches
D: Many sticking
2) Matching with fixing unit
After completion of the printout test, scratches on the surface of the fixing film and the fixing state of the residual toner were visually evaluated.
A: Not generated
B: Slight adhesion is observed
C: There are sticking and scratches
D: Many sticking
The obtained results are shown in Table 3.
[0225]
[Table 3]

[0226]
According to the present invention, it is possible to provide a magnetic toner that is excellent in charging uniformity and fixability and can obtain a high-definition image.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus for carrying out an image forming method of the present invention.
FIG. 2 is a schematic configuration diagram of an image forming apparatus for carrying out the image forming method of the present invention.
[Explanation of symbols]
100 photosensitive drum
102 Development sleeve (toner carrier)
104 Magnet roller
114 Transfer roller
116 Cleaner
117 Charging roller (contact charging member)
121 Laser generator
124 register roller
125 Conveyor belt
126 Fixing device
140 Developer

Claims (7)

In a magnetic toner having toner particles containing at least a binder resin component and iron oxide,
i) The ratio (B / A) of the content (B) of the iron element to the content (A) of the carbon element present on the toner particle surface as measured by X-ray photoelectron spectroscopy is less than 0.001;
ii) a projected area equivalent diameter of the magnetic toner C, a transmission electron using a microscope (TEM), magnification 10,000 times definitive in cross section of the magnetic toner is observed with iron oxide particle surfaces and toner particle surface When the minimum value of the distance is D, the magnetic toner satisfying the relationship of D / C ≦ 0.02 is 50% by number or more,
iii) The average circularity of the magnetic toner is 0.970 or more,
iv) In the molecular weight distribution measured by gel permeation chromatography (GPC) of the THF soluble content of the magnetic toner, there is a peak top of the main peak in the molecular weight range of 5000 to 50000, and X calculated from the following formula (1) Is 1.4 or less,

Possess V) inorganic fine powder to the toner particle surfaces,
VI) The magnetic toner , wherein the binder resin component contains at least a polymer obtained by polymerizing a monomer containing at least a styrene monomer using an organic peroxide .   In the molecular weight distribution measured by GPC of the THF soluble part of the magnetic toner, the component having a molecular weight of 300,000 or more is less than 20% by area and the molecular weight is 2000 to 5000 with respect to the total area of the soluble component derived from the binder resin component. The magnetic toner according to claim 1, wherein the component is less than 15 area%. The iron oxide is iron oxide obtained by hydrophobizing iron oxide particles generated from an aqueous solution containing ferrous hydroxide in an aqueous medium without passing through a drying step. The magnetic toner described.   The magnetic binder according to any one of claims 1 to 3, wherein the binder resin component includes a polymer obtained by radical polymerization of a monomer in the presence of a chain transfer agent. toner.   The toner particles are obtained by suspension polymerization of a monomer composition containing at least a monomer, a crosslinking agent, a hydrophobized iron oxide, a wax component, and a chain transfer agent in a water-based medium using a polymerization initiator. 5. The magnetic toner according to claim 1, wherein the toner particles are obtained as described above. A charging step of applying a voltage to the charging member to charge the image carrier;
An electrostatic latent image forming step of forming an electrostatic latent image on a charged image carrier;
A development region is formed by disposing an image carrier that holds the electrostatic latent image on the surface and a toner carrier that carries the magnetic toner on the surface, and in the development region, the magnetic toner is placed in the static region. A developing step of transferring the toner image to an electrostatic latent image and forming a toner image on the image carrier;
A transfer step of electrostatically transferring a toner image formed on the image carrier to a transfer material, and an image forming method in which image formation is repeatedly performed on the image carrier.
The image forming method according to claim 1, wherein the magnetic toner is the magnetic toner according to claim 1. The toner is transferred to an electrostatic latent image formed on an image carrier and visualized to form a toner image, and the toner image is transferred to a transfer material to be removable from an image forming apparatus that forms the image. Process cartridge,
The process cartridge has an image carrier, charging means for charging the image carrier to a predetermined potential, and toner, and transfers the toner to an electrostatic latent image formed on the image carrier for visualization. And a developing means for forming a toner image,
The process toner according to claim 1, wherein the toner is a magnetic toner according to claim 1.

Images